Foliar application of zinc and boron alleviate deficiency stress in papaya (Carica papaya L.) seedlings

Foliar application of zinc and boron alleviate deficiency stress in papaya (Carica papaya L.) seedlings | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Foliar application of zinc and boron alleviate deficiency stress in papaya ( Carica papaya L . ) seedlings Prahlad Deb, KumarAbhishek, Payel Das This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5890450/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Papaya is among the most important tropical fruits and is cultivated in nearly all Indian states. Micronutrient deficiency at an early stage can lead to poor growth and reduced yield in papaya. The effect of foliar application of zinc and boron on stress metabolism of papaya seedlings has been studied through a pot experiment conducted under greenhouse conditions. The experiment was framed in a completely randomised design with nine treatments that included zinc sulphate @ 0.2%, 0.4% and borax @ 0.2%, 0.4% and their combinations along with a control treatment (distilled water only). Seedlings were grown in polythene bags filled with properly washed sand and sprayed with the above treatment combinations of micronutrients at 15 days interval after germination adjusting neutral pH. The foliar spray of 0.4% zinc sulphate combined with 0.2% borax led to an increase in leaf chlorophyll content (a, b, and total), thereby boosting photosynthesis (soluble sugars) and enhancing the relative water content in leaves available for all metabolic processes. Increased application of zinc and boron also reduced the stress expression of papaya seedlings by reducing proline content, superoxide dismutase enzyme and phenol content. Lipid peroxidation in the leaf was also minimal with higher zinc application and moderate boron application, as indicated by the lower malondialdehyde content. Therefore, foliar application of 0.4% zinc sulphate and 0.2% borax can be recommended for better seedling growth of papaya in terms of less stress and high metabolic activity. Horticulture Plant Physiology and Morphology Zinc boron papaya seedlings SOD proline MDA phenol Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Papaya ( Carica papaya L.) is one of India's most commercially and nutritionally important fruit crops under the family Caricaceae. It is a tropical fruit crop which can grow well in subtropical environments. The plant is also identified as the "melon tree" and the "common man's fruit” (Lay et al. 2013 ).This fruit is full of nutrients as an abundant source of vitamin A and considered as good source of ascorbic acid. It is a rich source of essential minerals like iron, calcium and phosphorus along with various antioxidants and quality sugars (Ranaet al. 2020 ). The enzyme papain extracted from the dried or powdered latex of green papaya fruits has immense industrial and medicinal significance (Reenaet al. 2022 ; Deb et al. 2009). This fruit come within the first row of choice among the others due to its characteristic flavor and its mouth-watering taste. Raw papaya is used as key ingredient in various vegetarian and non-vegetarian culinary preparations, including various processed products like beverages, jam, jelly, candies, marmalade, soup, puree, juice, frozen slices or chunks, mixed beverages etc. (Sharma et al. 2023). Papaya actually originates from the Caribbean coast of Central America and has spread its cultivation throughout the tropics and subtropics of the world (Gabriela and Jorge, 2014 ). Commercial cultivation of papaya is present worldwide in the countries of Asia, Africa, America and even some subtropical regions of Europe (Mariana and Juan 2017 ; Baiyeri 2006 ). Papaya cultivation is widespread in India, with major production in the states of Tamil Nadu, Gujarat, Karnataka, Bihar, Jharkhand, Maharashtra, Uttarakhand, West Bengal and Andhra Pradesh (Rao et al. 2023 ). The substantial papaya production in this enormous country not only meets domestic demand but also significantly contributes to the export market, establishing India as a major player in the global papaya industry. The year-round fruiting capability of improved varieties and hybrids, coupled with high productivity and versatile uses, positions the papaya industry with substantial growth potential. As a resilient and adaptable crop, papaya plays a pivotal role in advancing sustainable agricultural practices, bolstering food security, and enhancing economic stability in the Indian agricultural landscape (Sonikommu et al. 2021). Apart from essential nutrients, various micronutrients significantly influence the growth, yield, fruit quality, and shelf life of papaya. Micronutrients viz. boron, zinc, copper, and iron are predominant for numerous cellular metabolic reactions, enzymatic processes, and overall development and growth of the papaya plant. Proper nutrition with micronutrients can support optimal growth, fruiting, yield and nutritional quality of papaya (Dahaiya 2018 ). Zinc plays a significant role in activating various enzymes and is engaged in metabolic processes, including the synthesis of growth hormones (Saini et al. 2019). It also aids plants in surviving with abiotic stresses such as droughts and heat waves. Zinc is essential for root development and facilitates rapid nutrient absorption by plants (Kumar et al. 2015 ). Zinc deficiency in plants causes stress, which can be mitigated through external zinc application (Kumari et al. 2022 ). Oxidative damage is common in zinc-deficient plants, leading to chlorotic symptoms and mottled leaves (Pandey et al. 2002 ). The use of zinc can alleviate the deficiency symptoms, in particular reducing the effect of the chlorophylase enzyme and thus reducing the rate of proline synthesis and thus the antioxidant activity in the plants (Bhadra et al. 2023 ). Metabolism of reactive oxygen species into normal nonreactive species and prevention of cell damage under appropriate environmental conditions are promoted by normal zinc nutrition in plants (Hasanuzzaman et al. 2020 ). The plant's tensile stress can be somehow reduced by proper zinc nutrition (Hassan et al. 2020 ). Boron is another vital micronutrient for papaya. It plays a large role in the formation and maintenance of plant cell walls and aids in sugar translocation. The supply of boron in sufficient quantity is necessary for the reproductive growth, fertilization process and fruit development of papaya (Modi et al. 2012 ). Boron in plants enhances antioxidant defenses, enabling them to neutralize reactive oxygen species (ROS) (Song et al. 2019 ; Tavallali et al. 2018 ; Liu et al. 2017 ). Deficiency in boron can lead to oxidative damage in cells and tissues (Ayvaz et al. 2016 ). The normal growth of the plant is also promoted by boron increasing cellular activity and reducing damage to chloroplasts, cell membranes and other cellular organelles through triggered autophagy processes (Wang et al. 2023 ; Riaz et al. 2018a ; Riaz et al. 2018b ). Boron toxicity can also lead to increased proline synthesis and higher malondialdehyde production, which are considered significant indicators of stress (Kohli et al. 2023 ; Chen et al. 2019). Zinc nutrition in plants also affects the movement of reactive oxygen species from source to sink (Mansoor et al. 2022 ). The toxicity of some other minerals can be remedied by the application of boron (Shireen et al. 2021 ). Boron can also alleviate migratory stress in plants (Aydin et al. 2019 ). Many scientists have carried out research to look over the impact of micronutrients on the yield and quality of papaya (Sarathkumar et al. 2022; Bhalerao and Patel 2012 ; Sekhar et al. 2010; Singh et al. 2005 ). However, there are no such works reporting the expression of stress in papaya seedlings using biochemical indicators in zinc and boron deficiency or toxicity. Therefore, the present research was probed to investigate the physiological expression of papaya seedlings on the basis of biochemical indicators under the influence of zinc and boron as foliar application. 2. Materials and methods 2.1. Location of experiment The location of the present investigation was Horticultural Farm, Department of Horticulture and Post-Harvest Technology, Palli-SikshaBhavana (Institute of Agriculture), Visva-Bharti, Srinikatan, West Bengal (23°42' N latitude and 87°40'30" E latitude, 40 m above mean sea level) during the year 2022–2023. The test site has a subtropical climate and the area lies under the red and lateritic zone of Semi-arid lateritic belt of West Bengal. Temperature range during summer months is high as 42–48℃ and 10–12℃ during the winter. The rainy season follows the summer from mid-July to late September experiencing an average annual rainfall of 1500 mm. 2.2. Raising of seedlings The seedlings were grown in greenhouse conditions in the poly bags filled with river sand. Coarse river sand was gathered from a riverbed, sieved to ensure uniform particle size, and meticulously washed to eliminate all clay and silt. This sand medium provided no plant nutrients, ensuring the control treatment confirmed the deficiency of the targeted nutrients, zinc and boron. Papaya seeds were soaked in water for overnight and treated with the mixture of carbendazim and mancozeb at a rate of 2g/kg of seeds before sowing in the poly bags. Germination began 15 days after sowing. The seedlings were provided foliar spray of urea at a concentration of 5g/L of water, starting 15 days post-germination, to provide nitrogen. The second application involved 10 granules of urea per plant, followed by the third and fourth applications of a 10:26:26 NPK mixture at 10 granules per plant, along with other nutrients (iron, copper, magnesium, sulfur, calcium, aluminum, molybdenum, etc.) at 15-day intervals. This nutrient application schedule was designed to identify any deficiency or stress symptoms (visual, physiological, and metabolic) specifically related to the deficiency of zinc and boron. Manual weeding and soil loosening were performed regularly. General recommended plant protection measures were also implemented. 2.3. Application of micronutrients, treatment detail and induction of stress condition Papaya seedlings were subjected to different doses and combinations of zinc and boron treatments, including a control group (without zinc and boron application), for evaluation of the performance under different conditions of nutrient sufficiency and deficiency, focusing on stress physiology. Zinc sulphate heptahydrate (ZnSO 4 , 7H 2 O) was selected as the zinc source, dissolved in water, and its pH was neutralized by adding lime. Borax (Na 2 B 4 O 7 ·10H 2 O) served as the boron source, dissolved in hot water. In combination treatments, zinc and borax sprays were applied with a 3-day interval between them. Three sets of sprays were administered, starting when the seedlings were 30 days old, with 15-day intervals between applications. The treatment combinations followed in the present research were T1: Zinc sulphate @ 0.2%; T2: Zinc sulphate @ 0.4%); T3: Borax @ 0.2%; T4: Borax @ 0.4%; T5: Zinc sulphate @ 0.2% + Borax @ 0.2%; T6: Zinc sulphate @ 0.2% + Borax @ 0.4%; T7: Zinc sulphate @ 0.4% + Borax @ 0.2%; T8: Zinc sulphate @ 0.4% + Borax @ 0.4% and T9: Control (only distilled water). Micronutrients were sprayed at fortnightly intervals. To induce stress conditions caused by the deficiency of either zinc, boron, or both, no applications of these micronutrients were made in certain treatments. This experimental strategy ultimately reflected in the leaf zinc and boron content of the papaya seedlings, which is proportionately correlated with physiological and metabolic responses to stress. 2.4. Recording observations The present experiment has included measurements of various plants physiological aspects and biochemical parameters related to different metabolic processes are as follows: 2.4.1. Determination of chlorophyll Dimethyl sulfoxide (DMSO) solvent was used to extract leaf chlorophyll after cutting the leaves in smaller pieces and placed in test tubes containing 10 ml of solvent, then incubated at 60–65ºC for one hour. Leaf tissue was cut into. Subsequently the samples were cooled to room temperature for 30 minutes, filtered and absorption measured at 665 nm and 648 nm being the final stages using DMSO as standard with LABMAN double beam UV-Visible spectrophotometer (LMSPUV 1200) (Sadasivam and Manickam, 1992). Chlorophyll concentration (a, b and total) was expressed as mg/g fresh weight and determined by the following formula (Barnes et al., 1992 ): Chlorophyll a (mg/g F.W) = (14.85 A 665 -5.14 A 648 ); Chlorophyll b (mg/g F.W) = (25.48 A 665 – 7.36 A 648 ); Total chlorophyll (mg/g F.W) = (7.49 A 665 + 20.34 A 648 ); where: A 665 = absorption value at 665 nm, A 648 = absorption value at 648 nm. 2.4.2. Stomatal density Determination of stomatal density was measured by the method described by Hultine and Marshall ( 2001 ). A thin layer of clear nail polish was applied to both surfaces of leaves collected from papaya plants across all treatments and a strip of clear stick tape was placed over the nail polish and pressed to stick with nail polish properly. Then the sticky tape has been peeled and the nail polish was fully come off with the tape. The tape with leaf impression was then placed on a microscope slide. The impression was placed from the other side of the leaf on the other part of the slide. The impression was then viewed under the microscope (Olympus SZ-61 SET, 6.7-45X, WHSZ 10X, Tokyo, Japan) at 100x or 400x magnification. The stomatal count was divided by the microscope's field of view area to determine stomatal density. 2.4.3. Relative water content of leaf Leaf discs were sampled (W) from the top-most fully expanded leaves using a sharp cork borer and kept in a pre-weighed airtight vial which was immediately placed in a picnic cooler (approximately 10°C-15°C). Subsequently, the samples were moistened to full turgidity for 3–4 hours under normal temperature. After hydration, the samples were removed, lightly wiped with filter or tissue paper and immediately weighed (fully turgid weight, TW). The samples were then oven-dried at 80°C for 24 hours and weighed (dry weight, DW). The relative water content of leaf was calculated with the following formula (Barr and Weatherley 1962 ): RWC (%) = [(W-DW) / (TW-DW)] x 100, where, W = Sample fresh weight, TW = Sample turgid weight and DW = Sample dry weight. 2.4.4. Soluble sugar content 50 ml clarified lead-free filtrate of leaf sample was taken in a 100 ml volumetric flask 5 ml of concentrated HCl and left for 24 hours at room temperature. The solution was subsequently neutralized first with concentrated NaOH solution, followed by 0.1N NaOH, using phenolphthalein as the endpoint indicator. Titration was done against Fehling's solution similar to the procedure of reducing sugars, thetotal sugar was determined as invert sugars (Lane and Eynon 1923 ). 2.4.5. Proline content 25 mg proline (Sigma Aldrich) dissolved to 250 ml as stock solution and standard samples were prepared (1, 2, 3, 4, 5, and 6 µgml − 1 proline). For each sample, spectrophotometric absorbance with LABMAN double beam UV-Visible spectrophotometer (LMSPUV 1200) was quantified using approximately 1 g tissue at 520 nm, according to the ninhydrin method (Bates et al. 1973 ). Subsequently, the proline content was derived from the standard curve prepared from known concentrations of the amino acids. 2.4.6. Super oxide dismutase activity (SOD) Activity of SOD has been determined using a biochemical method where xanthine-xanthine oxidase generates O 2 − , and nitroblue tetrazolium (NBT) reduction serves as an indicator of O 2 − production. SOD and NBT both reacts with O 2 − . the percent inhibition of NBT reduction is a measure of the amount of SOD present (Oberley and Spitz 1985 ; Spitz and Oberley 1989 ). Catalase was included to remove H 2 O 2 produced by SOD. 2.4.7. Phenol content The total phenolic contents of the ethanolic extract of papaya leaves were determined using the FolinCiocalteau reagent (Singleton and Rossi 1965 ) plotting the calibration curve by mixing 1 ml of Gallic acid solutions of different increasing concentrations with 5.0 ml of FolinCiocalteu reagent and 4.0 ml of sodium carbonate solution. Absorbance was measured after 30 minutes at 765 nm. A separate mixture of 1 ml of ethanolic extract (1 g/100 ml) with the same reagents was prepared and optical density was measured after 1 hour to calculate the total phenolic content. 2.4.8. Antioxidation capacity The total antioxidant capacity (TAC) of samples was derived following the method described by Prieto et al. ( 1999 ). Samples or standards at different concentrations (12.5–150 µg/mL) were mixed with a reaction mixture containing 0.6 M sulfuric acid, 28 mM sodium phosphate, and 1% ammonium molybdate in test tubes which was incubated at 95°C for 10 minutes to complete the reaction. Absorbance was noted at 695 nm using a spectrophotometer against blank solution. Increased optical density value of the reaction mixture indicates higher total antioxidant capacity, assuming that this concentration range is suitable for accurate calculations of IC 50 . 2.4.9. Lipid peroxidation (malondialdehyde or MDA content) MDA content determination was conducted following the method of Velikova et al. ( 2000 ) with some modifications. Fresh leaves (0.5 g) were ground with 5 mL of 0.1% trichloroacetic acid (TCA) and the extract was centrifuged (14,000 rpm for 5 minutes). 1 ml of supernatant was mixed with 4.5 ml of 0.5% thiobarbituric acid (TBA) and heated in a boiling water bath for 30 min. Reaction was stopped by cooling on ice. Absorbance was detected with three replications at 532 and 600 nm. 2.4.10. Leaf zinc content Leaf zinc content in papaya has been by the method of Koscielniak et al. ( 2021 ). Papaya leaves were washed, dried, grounded and mixed with a mixture of nitric acid and perchloric acid for digestion for complete release of zinc ions from the sample. The filtered solution was appropriately diluted within the calibration range of the Atomic Absorption Spectrometer (PerkinElmer Model-PINAACLE 900T, Germany), where a hollow cathode lamp emitted light at a specific wavelength (excitation wavelength and emission wavelength from 390 nm to 394 nm and from 540 to 550 nm respectively) absorbed by zinc atoms. The extent of absorption is proportional to the zinc concentration, allowing for quantitative analysis. A calibration curve with known zinc standards is used to quantify the zinc content in the plant sample. 2.4.11. Leaf boron content The Azomethane H method for boron determination in leaves of papaya plants under the present study included digestion samples with sulfuric acid (concentrated), followed by treatment with Azomethane H and hydrogen peroxide. This forms a yellow complex with boron, enabling precise measurement through spectrophotometry (Spencer and Erdman 1979). An azomethine H derivative (the yellow complex) is considered as spectrophotometric reagent for boron, as compared with azomethine H as blank and maximum absorption is recordedat 425 nm in double beam UV-Visible spectrophotometer (Labman, LMSPUV1900). 2.5.Statistical analyses The data were statistically analysed with ANOVA and Fisher’s least significant differences (LSD) at p < 0.05 were used to differentiate the treatment means with IBM SPSS Statistics (Version 26.0). The differences among the treatments were tested with critical difference (CD) value at a significance level of 5%, as recommended by Gomez and Gomez ( 1984 ). 3. Results The physiological and metabolic response to stress in papaya seedlings was notably affected by foliar application of varying doses of zinc and boron in the current experiment. Detailed discussions and interpretations of the mean data on various parameters are provided below: 3.1. Leaf chlorophyll content Chlorophyll a: Foliar zinc and boron a pplication influenced the cholorophyll production in the chloroplasts of the leaves of papaya seedlings (Table 1 and Fig. 1 ). Significantly maximum amount of chlorophyll a (196.1 mg/100g) was noted under the treatment T 7 (ZnSO 4 @ 0.4% + Borax @ 0.2%). T 6 (ZnSO 4 @ 0.2% + Borax @ 0.4%) also contained a good amount of chlorophyll a (169.2mg/100g). On the other hand T 9 or control treatment (no application of zinc and boron) has exhibited significantly minimum chlorophyll a content (130.6 mg/100g). Chllorophyll b : In the present experiment maximum amount of chlorophyll b (69.0 mg/100g0 was noted under treatment T 7 (ZnSO 4 @ 0.4% + Borax @ 0.2%) which was statistically in line with the plants under the treatment T 6 (ZnSO 4 @ 0.2% + Borax @ 0.4%) with 62.7 mg/100g chlorophyll b content (Table 1 and Fig. 1 ). Total chlorophyll : Foliar application of zinc and boron and their combinations also influenced the total chlorophyll content of papaya seedlings in our study (Table 1 and Fig. 1 ). The maximum amount of total chlorophyll (265.1mg/100g) in the papaya leaves has been observed under T 7 (ZnSO 4 @ 0.4% + Borax @ 0.2%) as significantly maximum which was indifferent with the total chlorophyll content in the papaya plants under the treatment T 5 (ZnSO 4 @ 0.2% + Borax @ 0.2%). Significantly lowest amount of total chlorophyll (176.8 mg/100g) was noted under T 9 or control treatment. 3.2. Stomatal density Foliar application of zinc and boron and their combination has greatly influenced the stomatal density of papaya leaves in the present study(Table 1 and Fig. 2 ).Papaya leaves exhibited significantly maximum density of stomata (657.4 per mm 2 leaf area) under the treatment T 7 (ZnSO 4 @ 0.4% + Borax @ 0.2%) and it was statistically similar in the plants of the treatment T 6 (ZnSO 4 @ 0.2% + Borax @ 0.4%) with a value of 635.6 numbers of stomata per mm 2 leaf area. Increased doss of zinc sulphate as well as borax has also increased the stomatal density. On contrary, significantly minimum stomatal density (422.6 per mm 2 leaf area) has been noted in the control treatment (T 9 ) under the deficiency of zinc and boron which indicated the stressfulness of the papaya seedlings. 3.3. Relative water content in leaves Relative water content in leaves in a certain condition indicates the water availability of the plants for its physiological process particularly the photosynthesis. Present experiment exhibited maximum relative water content of papaya leaves (Table 1 and Fig. 3 ) showed maximum physiological activity under treatment combination T 7 (ZnSO 4 @ 0.4% + Borax @ 0.2%) with significantly highest relative water content (87.3%). The control treatment (T 9 ) has shown the minimum relative water content in leaves (71.2%) indicating the lowest physiological availability of water and thus in stress condition and treatment T 1 (ZnSO 4 @ 0.2%) has not exhibited any difference with T 9 with regard to relative water content of leaf. 3.4. Soluble sugar content The photosynthates in form of soluble sugar in leaves are the clear indicator of photosynthetic activity of the plants which depends upon the chlorophyll content, stomatal density and relative water content in leaves. The leaves having high chlorophyll content, good stomatal density and higher relative water content, always stands for greater photosynthates. The findings of the current research revealed that the application of zinc and boron has greatly influenced the photosynthetic rate (Table 1 and Fig. 3 ). Maximum photosynthates in form of soluble sugar (75.6mg/g) was noted in the treatment T 7 (ZnSO 4 @ 0.4% + Borax @ 0.2%) having good amount of zinc and boron. Other treatments with adequate zinc and boron application have also exhibited significant amount of soluble sugar. Being stressed condition in the treatment T 9 or control having no zinc and boron, the plants produced significantly minimum amount of soluble sugar (42.7mg/g) being under less photosynthetic activity. 3.5. Leaf proline content Proline accumulation occurs in plant parts under stressful conditions caused by various abiotic and biotic factors, including adverse environmental conditions, nutrient deficiencies, and mineral toxicity. It is also reported as measure of osmolite to mitigate oxidative stress by scavenging reactive oxygen species. In the current research, the proline content of papaya leaves varied significantly along the application of varying doses of zinc and boro (Table 2 and Fig. 4 ). Increased doses of zinc and boron resulted decrease in leaf proline content in papaya leaves. Application of ZnSO 4 @ 0.4% with Borax @ 0.2% (T 7 ) has recorded proline of 22.1 µmole/g fresh weight which was lowest and statistically indifferent with T 8 (ZnSO 4 @ 0.4% with Borax @ 0.4%) which exhibited proline content 23.1 µmole/g fresh weight. Significantly maximum leaf proline content (45.2 µmole/g fresh weight) was noticed under control or no application of zinc and boron which indicated the stressed condition of papaya seedlings under micronutrient deficiency and on contrary comfort situation of plants under T 7 and T 8 . 3.6. Superoxide dismutase (SOD) Superoxide dismutase is an enzyme that facilitates the dismutation of superoxide radicals produced within the plant system under stress conditions. This process converts superoxides into non-reactive oxygen molecules and peroxide, thereby preventing oxidative damage to plant cell parts and organelles. Plants increase their production of SOD in response to stress conditions to mitigate oxidative damage. The findings of the current research indicates that the SOD production have been decreased with increasing doses or in the absence of zinc and boron (Table 2 and Fig. 4 ) led the plants under greater stress as indicated by significantly highest SOD content (36.5 unit/mg) under control treatment (T 9 ). On the other hand lowest SOD activity (15.8 unit/mg) has been recorded under T 7 (ZnSO 4 @ 0.4% with Borax @ 0.2%) and it was closely set by T 8 (ZnSO 4 @ 0.4% with Borax @ 0.4%) with SOD activity of 18.4 unit/mg. 3.7. Leaf total phenol Various phenolic compounds have the potential to effectively scavenge harmful reactive oxygen species. The phenyl propanoid biosynthetic pathway is activated under different plant stress conditions, leading to the accumulation of various types of phenols in plants. Papaya seedlings under control treatment (T 9 ) has produced a considerable highest amount of phenol (43.7 mgGAE/100g) while on contrary T 8 (ZnSO 4 @ 0.4% with Borax @ 0.4%) and T 7 (ZnSO 4 @ 0.4% with Borax @ 0.2%) has exhibited lower quantity of phenol in papaya leaves as 18.2 and 21.5 mgGAE/100g respectively(Table 2 and Fig. 4 ). Thus the plants under control treatment with no micronutrient application were under stress condition and in other treatments of zinc and boron application they were in comfort. 3.8. Antioxidation capacity (DPPH radical scavenging %) Under biotic and abiotic stress conditions, plants experience increased production of reactive oxygen species (ROS), causes oxidative stress induction. Plants inherently possess the capacity to synthesize non-enzymatic antioxidants under normal conditions, which counter the oxidative stress of ROS (Wang et al., 2009 ; Xu et al., 2003 and Kayihan et al., 2016 ). The findings of the current study revealed that the foliar application of zinc and boron in sufficient quantity resulted the higher antioxidant production (Table 2 and Fig. 5 ) reflected by significant maximum under T 8 (ZnSO 4 @ 0.4% with Borax @ 0.4%) i.e. 76.6% DPPH radical scavenging and it was statistically alike with T 7 (ZnSO 4 @ 0.4% with Borax @ 0.2%) and showed 73.1% DPPH radical scavenging. On contrary, the control treatment (T 9 ) has exhibited lowest antioxidation capacity (58.7% DPPH radical scavenging) and it was similar with T 1 (ZnSO 4 @ 0.2%, recorded 62.7% DPPH radical scavenging). 3.9. Lipid peroxidation (MDA content) Lipid peroxidation is a deleterious process in plants. It affects membrane properties, causes protein degradation and limits the capacity of ionic transport due to high, ultimately triggering the cell death process. The production of ROS in greater quantity causes more lipid peroxidation which is detected by greater quantity of MDA as it is the final product of peroxidation of polyunsaturated fatty acids in the cells. The findings of the present research exhibited the significantly maximum lipid peroxidation (Table 2 and Fig. 5 ) was taken place in the papaya plants under control treatment (T 9 ) and that was indicated by highest MDA content of leaves (67.4 µ mole/g FW). Significantly lowest MDA content was recorded in the plants under T 7 (ZnSO 4 @ 0.4% with Borax @ 0.2%) i.e. 34.0 µ mole/g FW. The other micronutrient treatments also exhibited lower MDA content in the papaya leaves that ranged up to 46.6 µ mole/g FW. 3.10. Leaf zinc and boron content Zinc accumulation in the leaves of papaya seedlings have been significantly varied within the treatment combinations in the present experiment (Table 2 and Fig. 6 ). Maximum zinc content in papaya leaves (22.2 µg/g dry leaf) was noted in T 8 (ZnSO 4 @ 0.4% with Borax @ 0.4%) which was in line with T 7 (ZnSO 4 @ 0.4% with Borax @ 0.2%) (21.6 µg/g dry leaf) and T 2 (ZnSO 4 @ 0.4%) (21.4 µg/g dry leaf).In all these cases application of zinc was done in highest concentration. Significantly lowest leaf zinc content (12.1 µg/g dry leaf) was noted in the plants under control treatment (T 9 ) having no zinc application. Highest boron content (17.1µg/g dry leaf) has been found in T 8 (ZnSO 4 @ 0.4% with Borax @ 0.4%) which was statistically in line with T 4 (Borax @ 0.4%) and T 6 (ZnSO 4 @ 0.2% + Borax @ 0.4%) with boron content of 17.0 and 16.7µg/g dry leaf respectively(Table 2 and Fig. 6 ). In all these treatments application of boron was in highest concentration. Control treatment (T 9 ) exhibited lowest amount of boron (6.8µg/g dry leaf) in the papaya leaves as there was no boron application and that was statistically similar with T 1 (ZnSO 4 @ 0.2%) and T 2 (ZnSO 4 @ 0.4%) having no boron application. 4. Discussion 4.1. Zinc and boron deficiency caused stress in the papaya seedlings that induced chlorosis, reduced stomatal density, relative water content in leaf and photosynthesis The combined application of zinc and boron increased different types and total chlorophyll levels in papaya plants, as observed in this experiment. Plants that were deficient in zinc and boron, without these micronutrients, showed chlorophyll deficiency or chlorotic symptoms. Under severe zinc and boron stress, some plants exhibited chlorosis and necrosis symptoms. Borowiak et al. ( 2015 ) demonstrated increased photosynthetic activity in Salix hybrid due to higher leaf chlorophyll content with zinc treatment. Jain et al. ( 2010 ) observed chlorophyll destruction due to oxidative damage caused by zinc deficiency in sugarcane. Xu et al. ( 2003 ) and Baycu et al. ( 2016 ) reported oxidative degradation of chlorophyll pigments under zinc deficiency conditions. Higher concentrations of zinc and boron improved stomatal density in papaya leaves likely due to proper leaf development and reduced stress resulting from adequate nutrient levels in this experiment. Tufail et al. ( 2018 ) found greater stability of leaf cell membranes and increased stomatal density of rice seedlings with sufficient zinc nutrition under salinity stress. Yin et al. ( 2022 ) reported lower stomatal density in Neolamarckia under boron deficiency. Liu et al. ( 2015 ) observed lower stomatal density and deformed stomata in trifoliate orange rootstock under boron and zinc deficiency conditions. Papaya plants treated with sufficient zinc and boron exhibited higher relative water content of leaves in treatment T 7 (ZnSO4 @ 0.4% + Borax @ 0.2%), indicating better physiological conditions compared to plants under the control treatment. Hernandez and Almansa ( 2002 ) reported reduced relative water content in pea leaves under stress conditions. Luis et al. ( 2012 ) observed lower leaf relative water content in tomato plants under boron deficiency and toxicity conditions. Similar findings were reported in safflower by Sulus and Leblebici ( 2020 ). Jabeen and Ahmad ( 2012a ) found increased relative water content in sunflower and safflower leaves with foliar application of zinc and boron, reducing stress. Treatment T 7 (ZnSO4 @ 0.4% + Borax @ 0.2%) evidenced the highest chlorophyll content, stomatal density, and relative water content in papaya leaves, potentially contributing to increased photosynthetic activity and higher soluble sugar production as photosynthates. Adequate nutrition of zinc and boron in papaya facilitated significant chlorophyll production and protected against oxidation. Shokat et al. ( 2020 ) reported increased sugar synthesis and higher yield in wheat grown under drought with micronutrient application, including zinc and boron. Xu et al. ( 2020 ) noted reduced photosynthesis and sugar production in alfalfa under various stresses, including nutritional stress. 4.2. Zinc and boron deficiency in papaya seedlings resulted activation of cellular stress mitigation strategies like higher proline, SOD, phenols, antioxidants etc. Higher proline content in plants under the control treatment (deficient in zinc and boron) indicated maximum stress, whereas proper application of zinc and boron together resulted in lower proline levels in the leaves. The increased proline accumulation was a response to cope with stress caused by micronutrient deficiency in this experiment. Sultana et al. ( 2016 ) observed reduced proline content in wheat under stress conditions after zinc application. Conversely, Yang et al. ( 2021 ) found higher proline content in zinc-deficient tobacco plants. Plants under the control treatment exhibited higher production of superoxide radicals, leading to increased levels of superoxide dismutase (SOD) for dismutation activity to mitigate stress effects. In contrast, papaya plants with adequate zinc and boron nutrition showed lower SOD content in their leaves. Song et al. ( 2019 ) reported increased SOD content in beet under boron-induced oxidative stress. Kakmak (2000) and Hasanuzzaman et al. ( 2020 ) observed higher SOD production to reduce ROS concentration under zinc deficiency in plants. Foyer ( 2018 ) and Mittler (2022) highlighted the positive role of zinc and boron in regulating ROS signalling responses in plants under stress. Choudhary et al. ( 2020 ) found oxidative damage indicated by higher SOD content in Mentha and Cymbopogon under zinc and boron stress. Under stress conditions caused by zinc and boron deficiency in the present research, higher production of total phenols was observed in plants under the control treatment to scavenge the reactive oxygen species produced. Conversely, proper zinc and boron nutrition resulted in lower production of leaf phenols. It has been described that zinc deficiency stress increases phenolic content of many plants grown under adverse weather conditions by activating phenyl propanoid biosynthetic pathways (Hassan et al., 2020 ; Hammerschmitt et al., 2020 ; Ann et al., 2001 ). Golkar ( 2018 ) found increased phenolic content in safflower leaves under micronutrient and salinity stress. Proper nutrition of papaya plants with zinc and boron application in this experiment resulted in higher antioxidation capacity, whereas deficient plants exhibited lower capacity to scavenge reactive oxygen species (ROS). Noreen et al. ( 2021 ) observed improved antioxidation capacity in barley with foliar zinc application. Similarly, Zoufan et al. ( 2018 ) reported enhanced antioxidation capacity and reduced oxidative damage in Chenopodium murale L. plants exposed to elevated zinc levels. Kayihan et al. ( 2016 ) found higher antioxidation capacity in Arabidopsis with boron application, and Wang et al. ( 2009 ) observed similar results in rapeseed seedlings. 4.3. Cellular damage in papaya seedlings caused due to zinc and born deficiency Lipid molecules in cell membranes, as well as unit membranes of other cell organelles, are highly susceptible to peroxidation, which leads to the production of malondialdehyde (MDA) and ultimately results in membrane damage, leakage, and loss of stability (John and Steven 1978 ). In the present experiment, papaya plants without application of zinc and boron (T9: control) exhibited higher lipid peroxidation rates and consequently higher MDA production due to physiological stress. Conversely, plants receiving proper zinc and boron application (T8: ZnSO4 @ 0.4% with Borax @ 0.4% and T7: ZnSO4 @ 0.4% with Borax @ 0.2%) may have been in a more comfortable physiological condition, resulting in lower lipid peroxidation (Marichali et al. 2016 ). Chen et al. ( 2022 ) observed higher MDA content in alfalfa under copper and zinc stress, consistent with findings by Jabeen and Ahmad (2012) in sunflower and safflower, and Shah et al. ( 2017 ) in Citrange. Normal ranges of zinc and boron content in papaya leaves have been published as 21.2 to 22.4 µg/g dry leaf and 16.1 to 17.3 µg/g dry leaf or more, respectively (Subedi et al. 2019 ; Nautiyal et al., 1986 ). Under deficiency conditions, zinc and boron content were noted to decrease to 11 to 13 µg/g dry leaf and 6.4 to 7.0 µg/g dry leaf or less, respectively (Vasanthu et al. 2015 ). Zinc deficiency was prominent in the control treatment (T9) as well as treatments T3 and T4, which received no zinc application. Similarly, boron deficiency was observed in the control treatment (T 9 ) as well as treatments T1 and T2, which received no boron application. Deficiencies of zinc and boron caused nutrient stress conditions in papaya seedlings, supported by quantification of antioxidative enzymes (SOD), proline, phenol production, and lipid peroxidation. 5. Conclusion In conclusion, the findings of the present experiment revealed the significant contribution of foliar application of zinc and boron on papaya seedlings particularly in physiological and metabolic processes. The application of zinc sulphate @ 0.4% along with borax @ 0.2% promoted the production of leaf chlorophyll (a, b and total) and thereby increased photosynthates (soluble sugar) along with greater relative water content in leaves available for all metabolic processes. Increased zinc and boron application also minimized the expression of stress in the papaya seedlings by reducing the proline content, superoxide dismutase enzyme as well as phenol content. The rate of lipid peroxidation in leaves was also minimized with higher rate of zinc application along with moderate boron application which was indicated by lower malondialdehyde content. Thus the research provides a proof that the papaya seedlings experienced stressed condition under deficiency of zinc and boron which is evident from stress mitigation strategies adopted by the plants under no application of zinc and boron with respect to physiological and cellular metabolic processes. Additionally, this stress condition can be overcome by the foliar application of zinc sulphate @ 0.4% and borax @ 0.2% which is beneficial for better seedling growth of papaya with respect to less stress and high metabolic activity. Declarations CRediT authorship contribution statement: Prahlad Deb: Writing – review & editing, Validation, Supervision, Resources, Project administration, Investigation, Conceptualization. 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J Plant Inter 16(1): 354–366. https://doi.org/10.1080/17429145.2021.1961886 Yin Q, Kang L, Liu Y, Qaseem MF, Qin W, Liu T, Li H, Deng X, Wu A (2022) Boron deficiency disorders the cell wall in Neolamarckiacadamba. Indust Crops Prod176(46): 114332.http://doi.org/10.1016/j.indcrop.2021.114332 Zoufan P, Karimiafshar A, Shokati S, Hassibi P, Rastegarzadeh S (2018) Oxidative damage and antioxidant response in Chenopodium murale L. exposed to elevated levels of Zn. Braz Arch Biol Tech61: e18160758. http://doi.org/10.1590/1678-4324-2018160758 Tables Table 1: Leaf chlorophyll content, stomatal density, relative leaf water content and soluble sugar content of papaya seedlings as influenced by foliar application of zinc and boron at 90 th day Treatments Chlorophyll a content (mg/100g FW) Chlorophyll b content (mg/100g FW) Total chlorophyll content (mg/100g FW) Stomatal density (per mm 2 ) Relative Leaf Water Content (%) Soluble sugar content (mg/g) T1 142.6±5.2 56.1±4.3 198.7±7.3 587.6±27.7 75.0±4.9 46.8±3.5 T2 152.7±7.1 53.7±4.0 206.4±9.1 610.9±28.9 77.5±4.1 48.2±4.2 T3 153.6±6.7 56.9±5.2 210.5±8.2 591.2±16.3 79.3±5.6 47.0±3.9 T4 148.7±8.1 52.3±4.9 201.0±7.0 598.5±22.5 81.1±7.2 58.5±4.1 T5 175.8±6.6 61.8±6.2 237.6±8.8 641.8±18.7 82.6±6.5 63.4±5.0 T6 169.2±7.3 62.7±5.8 231.9±7.6 635.6±24.3 81.6±7.4 68.9±4.7 T7 196.1±9.7 69.0±6.7 265.1±9.5 657.4±19.9 87.3±6.1 75.6±6.5 T8 153.5±5.9 56.9±5.5 210.4±9.8 609.2±15.7 80.7±5.9 65.2±6.8 T9 130.6±7.5 46.2±4.3 176.8±6.4 422.6±14.3 71.2±5.7 42.7±5.7 SE(m) 3.73 2.4 5.5 5.1 1.88 2.51 CD(0.05) 11.2 7.4 16.4 15.4 5.64 7.54 T 1 :ZnSO 4 @ 0.2%, T 2 :ZnSO 4 @ 0.4%, T 3 : Borax @ 0.2%, T 4 :Borax @ 0.4%, T 5 :ZnSO 4 @ 0.2% + Borax @ 0.2%, T 6 :ZnSO 4 @ 0.2% + Borax @ 0.4%, T 7 :ZnSO 4 @ 0.4% + Borax @ 0.2%, T 8 :ZnSO 4 @ 0.4% + Borax @ 0.4%, T 9 (Control) Table 2: Physio-metabolic expression of papaya seedlings and leaf zinc and boron as influenced by foliar application of zinc and boron at 90 th day Treatments Leaf proline content (µ mole/g FW) Superoxide dismutase (SOD) unit/mg Phenol (mgGAE/100g) Antioxidation capacity (DPPH radical scavenging %) Lipid peroxidation (MDA) (µ mole/g FW) Zinc content in leaves (µg/g dry weight) Boron content in leaves (µg/g dry weight) T1 31.5±2.9 27.4±2.8 31.3±4.1 62.7±5.8 46.6±3.7 17.3±2.7 7.1±0.9 T2 30.2±3.2 22.1±2.7 30.8±3.5 69.2±5.5 42.2±4.2 21.4±2.0 6.9±0.7 T3 29.3±2.7 29.5±3.4 38.4±3.8 59.8±5.1 41.6±5.3 12.6±1.8 12.5±1.0 T4 28.6±2.5 26.3±3.9 35.1±3.1 61.3±5.8 39.1±3.7 13.0±1.5 17.0±1.9 T5 26.3±3.4 21.7±2.3 26.7±2.9 66.4±6.3 40.5±3.8 18.0±1.7 11.9±1.0 T6 24.4±2.0 20.2±2.8 24.5±2.7 68.2±6.4 39.3±2.7 17.8±1.6 16.7±1.8 T7 22.1±3.5 15.8±1.9 21.5±2.3 73.1±6.2 34.0±4.3 21.6±1.9 12.4±1.4 T8 23.1±3.1 18.4±2.1 18.2±2.1 76.6±5.9 39.8±4.0 22.2±1.8 17.1±1.5 T9 45.2±3.9 36.5±4.2 43.7±3.9 58.7±6.4 67.4±5.8 12.1±1.4 6.8±0.8 SE(m) 0.91 1.21 2.2 2.85 1.41 0.54 0.47 CD(0.05) 2.73 3.52 6.7 8.59 4.22 1.63 1.42 T 1 :ZnSO 4 @ 0.2%, T 2 :ZnSO 4 @ 0.4%, T 3 : Borax @ 0.2%, T 4 :Borax @ 0.4%, T 5 :ZnSO 4 @ 0.2% + Borax @ 0.2%, T 6 :ZnSO 4 @ 0.2% + Borax @ 0.4%, T 7 :ZnSO 4 @ 0.4% + Borax @ 0.2%, T 8 :ZnSO 4 @ 0.4% + Borax @ 0.4%, T 9 (Control). Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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Deb","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYDCCAzxAooBZjoGBhyQtBszGpGtJbCBaC9/x3mOPKwys0zccP3vwwQcGOzndBgJaJM+cSzc8Y5Ceu+FMXrLhDIZkY7MDBLQY3Mgxk2wwOJy74UCOmTQPw4HEbQS13H8D1pJucP4NsVpu8IC1JICsI06L5Jm8dMMGg3TDmTfeGBvOMCDCL3zHzx572FBhLc93PsfwwYcKOzmCWoCADUwqgFUaEFaO0CLfQJzqUTAKRsEoGIEAAH+LREr/5tTjAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0003-0725-7776","institution":"Institute of Agriculture, Visva-Bharati","correspondingAuthor":true,"prefix":"","firstName":"Prahlad","middleName":"","lastName":"Deb","suffix":""},{"id":406310432,"identity":"8c3a356a-a9c5-4ffb-9fb0-48bb237109bb","order_by":1,"name":"KumarAbhishek","email":"","orcid":"https://orcid.org/0009-0009-0030-7073","institution":"Institute of Agriculture, Visva-Bharati","correspondingAuthor":false,"prefix":"","firstName":"","middleName":"","lastName":"KumarAbhishek","suffix":""},{"id":406310639,"identity":"31351c67-9df6-49ef-9b69-eef8618965d7","order_by":2,"name":"Payel Das","email":"","orcid":"https://orcid.org/0000-0002-6325-9314","institution":"Institute of Agriculture, Visva-Bharati","correspondingAuthor":false,"prefix":"","firstName":"Payel","middleName":"","lastName":"Das","suffix":""}],"badges":[],"createdAt":"2025-01-23 18:29:23","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-5890450/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5890450/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":74909056,"identity":"fb1d0757-e6c9-4823-a2b7-25f2e534ad03","added_by":"auto","created_at":"2025-01-28 08:43:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":31386,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eChlorophyll content (a, b and total) of papaya leaves under different doses of foliar application of zinc and boron.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5890450/v1/ff2e4e0ee5af4d93e28acccd.png"},{"id":74909052,"identity":"90345ae5-2a43-4bfa-ac39-f535b42074ee","added_by":"auto","created_at":"2025-01-28 08:43:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":23265,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStomatal density of papaya leaves under different doses of foliar application of zinc and boron.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5890450/v1/87d7f50ce05c8b5e89facb53.png"},{"id":74909054,"identity":"5947b260-1a7d-4df1-a714-3a31907935da","added_by":"auto","created_at":"2025-01-28 08:43:29","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":28276,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRelative leaf water content and soluble sugar content of papaya leaves under different doses of foliar application of zinc and boron.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5890450/v1/0304961fe24e2c3d4823a267.png"},{"id":74910475,"identity":"851b9899-6462-4c17-96e6-0ab19ae6113e","added_by":"auto","created_at":"2025-01-28 08:59:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":35217,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProline content, super oxide dismutase and phenol content of papaya leaves under different doses of foliar application of zinc and boron.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5890450/v1/a04c6e2f759b4ca34a75a104.png"},{"id":74909057,"identity":"31b3acf0-e8c0-4d72-8815-9db5db6d387d","added_by":"auto","created_at":"2025-01-28 08:43:29","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":26502,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAntioxidation capacity and lipid peroxidation of papaya leaves under different doses of foliar application of zinc and boron.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5890450/v1/08dad4d9bfffaa4ac5d87e53.png"},{"id":74909064,"identity":"92b2a881-5f66-4d07-931a-d7c6ab6268f2","added_by":"auto","created_at":"2025-01-28 08:43:29","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":19209,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ezinc content and boron content of papaya leaves under different doses of foliar application of zinc and boron.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5890450/v1/bbc0815913a5c49a736ed9c8.png"},{"id":74910988,"identity":"478da143-baf5-44c4-a019-4046a80cc10c","added_by":"auto","created_at":"2025-01-28 09:07:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2080296,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5890450/v1/d5bd0666-720d-451f-a32e-3da63f10ca53.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eFoliar application of zinc and boron alleviate deficiency stress in papaya (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eCarica papaya \u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eL\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e) seedlings\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003ePapaya (\u003cem\u003eCarica papaya\u003c/em\u003e L.) is one of India's most commercially and nutritionally important fruit crops under the family Caricaceae. It is a tropical fruit crop which can grow well in subtropical environments. The plant is also identified as the \"melon tree\" and the \"common man's fruit\u0026rdquo; (Lay et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).This fruit is full of nutrients as an abundant source of vitamin A and considered as good source of ascorbic acid. It is a rich source of essential minerals like iron, calcium and phosphorus along with various antioxidants and quality sugars (Ranaet al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The enzyme papain extracted from the dried or powdered latex of green papaya fruits has immense industrial and medicinal significance (Reenaet al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Deb et al. 2009). This fruit come within the first row of choice among the others due to its characteristic flavor and its mouth-watering taste. Raw papaya is used as key ingredient in various vegetarian and non-vegetarian culinary preparations, including various processed products like beverages, jam, jelly, candies, marmalade, soup, puree, juice, frozen slices or chunks, mixed beverages etc. (Sharma et al. 2023).\u003c/p\u003e \u003cp\u003ePapaya actually originates from the Caribbean coast of Central America and has spread its cultivation throughout the tropics and subtropics of the world (Gabriela and Jorge, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Commercial cultivation of papaya is present worldwide in the countries of Asia, Africa, America and even some subtropical regions of Europe (Mariana and Juan \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Baiyeri \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Papaya cultivation is widespread in India, with major production in the states of Tamil Nadu, Gujarat, Karnataka, Bihar, Jharkhand, Maharashtra, Uttarakhand, West Bengal and Andhra Pradesh (Rao et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The substantial papaya production in this enormous country not only meets domestic demand but also significantly contributes to the export market, establishing India as a major player in the global papaya industry. The year-round fruiting capability of improved varieties and hybrids, coupled with high productivity and versatile uses, positions the papaya industry with substantial growth potential. As a resilient and adaptable crop, papaya plays a pivotal role in advancing sustainable agricultural practices, bolstering food security, and enhancing economic stability in the Indian agricultural landscape (Sonikommu et al. 2021).\u003c/p\u003e \u003cp\u003eApart from essential nutrients, various micronutrients significantly influence the growth, yield, fruit quality, and shelf life of papaya. Micronutrients viz. boron, zinc, copper, and iron are predominant for numerous cellular metabolic reactions, enzymatic processes, and overall development and growth of the papaya plant. Proper nutrition with micronutrients can support optimal growth, fruiting, yield and nutritional quality of papaya (Dahaiya \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Zinc plays a significant role in activating various enzymes and is engaged in metabolic processes, including the synthesis of growth hormones (Saini et al. 2019). It also aids plants in surviving with abiotic stresses such as droughts and heat waves. Zinc is essential for root development and facilitates rapid nutrient absorption by plants (Kumar et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Zinc deficiency in plants causes stress, which can be mitigated through external zinc application (Kumari et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Oxidative damage is common in zinc-deficient plants, leading to chlorotic symptoms and mottled leaves (Pandey et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). The use of zinc can alleviate the deficiency symptoms, in particular reducing the effect of the chlorophylase enzyme and thus reducing the rate of proline synthesis and thus the antioxidant activity in the plants (Bhadra et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Metabolism of reactive oxygen species into normal nonreactive species and prevention of cell damage under appropriate environmental conditions are promoted by normal zinc nutrition in plants (Hasanuzzaman et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The plant's tensile stress can be somehow reduced by proper zinc nutrition (Hassan et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBoron is another vital micronutrient for papaya. It plays a large role in the formation and maintenance of plant cell walls and aids in sugar translocation. The supply of boron in sufficient quantity is necessary for the reproductive growth, fertilization process and fruit development of papaya (Modi et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Boron in plants enhances antioxidant defenses, enabling them to neutralize reactive oxygen species (ROS) (Song et al. \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Tavallali et al. \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Deficiency in boron can lead to oxidative damage in cells and tissues (Ayvaz et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The normal growth of the plant is also promoted by boron increasing cellular activity and reducing damage to chloroplasts, cell membranes and other cellular organelles through triggered autophagy processes (Wang et al. \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Riaz et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e; Riaz et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018b\u003c/span\u003e ). Boron toxicity can also lead to increased proline synthesis and higher malondialdehyde production, which are considered significant indicators of stress (Kohli et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Chen et al. 2019). Zinc nutrition in plants also affects the movement of reactive oxygen species from source to sink (Mansoor et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The toxicity of some other minerals can be remedied by the application of boron (Shireen et al. \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Boron can also alleviate migratory stress in plants (Aydin et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMany scientists have carried out research to look over the impact of micronutrients on the yield and quality of papaya (Sarathkumar et al. 2022; Bhalerao and Patel \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Sekhar et al. 2010; Singh et al. \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). However, there are no such works reporting the expression of stress in papaya seedlings using biochemical indicators in zinc and boron deficiency or toxicity. Therefore, the present research was probed to investigate the physiological expression of papaya seedlings on the basis of biochemical indicators under the influence of zinc and boron as foliar application.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Location of experiment\u003c/h2\u003e \u003cp\u003eThe location of the present investigation was Horticultural Farm, Department of Horticulture and Post-Harvest Technology, Palli-SikshaBhavana (Institute of Agriculture), Visva-Bharti, Srinikatan, West Bengal (23\u0026deg;42' N latitude and 87\u0026deg;40'30\" E latitude, 40 m above mean sea level) during the year 2022\u0026ndash;2023. The test site has a subtropical climate and the area lies under the red and lateritic zone of Semi-arid lateritic belt of West Bengal. Temperature range during summer months is high as 42\u0026ndash;48℃ and 10\u0026ndash;12℃ during the winter. The rainy season follows the summer from mid-July to late September experiencing an average annual rainfall of 1500 mm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Raising of seedlings\u003c/h2\u003e \u003cp\u003eThe seedlings were grown in greenhouse conditions in the poly bags filled with river sand. Coarse river sand was gathered from a riverbed, sieved to ensure uniform particle size, and meticulously washed to eliminate all clay and silt. This sand medium provided no plant nutrients, ensuring the control treatment confirmed the deficiency of the targeted nutrients, zinc and boron. Papaya seeds were soaked in water for overnight and treated with the mixture of carbendazim and mancozeb at a rate of 2g/kg of seeds before sowing in the poly bags. Germination began 15 days after sowing. The seedlings were provided foliar spray of urea at a concentration of 5g/L of water, starting 15 days post-germination, to provide nitrogen. The second application involved 10 granules of urea per plant, followed by the third and fourth applications of a 10:26:26 NPK mixture at 10 granules per plant, along with other nutrients (iron, copper, magnesium, sulfur, calcium, aluminum, molybdenum, etc.) at 15-day intervals. This nutrient application schedule was designed to identify any deficiency or stress symptoms (visual, physiological, and metabolic) specifically related to the deficiency of zinc and boron. Manual weeding and soil loosening were performed regularly. General recommended plant protection measures were also implemented.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Application of micronutrients, treatment detail and induction of stress condition\u003c/h2\u003e \u003cp\u003ePapaya seedlings were subjected to different doses and combinations of zinc and boron treatments, including a control group (without zinc and boron application), for evaluation of the performance under different conditions of nutrient sufficiency and deficiency, focusing on stress physiology. Zinc sulphate heptahydrate (ZnSO\u003csub\u003e4\u003c/sub\u003e, 7H\u003csub\u003e2\u003c/sub\u003eO) was selected as the zinc source, dissolved in water, and its pH was neutralized by adding lime. Borax (Na\u003csub\u003e2\u003c/sub\u003eB\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026middot;10H\u003csub\u003e2\u003c/sub\u003eO) served as the boron source, dissolved in hot water. In combination treatments, zinc and borax sprays were applied with a 3-day interval between them. Three sets of sprays were administered, starting when the seedlings were 30 days old, with 15-day intervals between applications. The treatment combinations followed in the present research were T1: Zinc sulphate @ 0.2%; T2: Zinc sulphate @ 0.4%); T3: Borax @ 0.2%; T4: Borax @ 0.4%; T5: Zinc sulphate @ 0.2% + Borax @ 0.2%; T6: Zinc sulphate @ 0.2% + Borax @ 0.4%; T7: Zinc sulphate @ 0.4% + Borax @ 0.2%; T8: Zinc sulphate @ 0.4% + Borax @ 0.4% and T9: Control (only distilled water). Micronutrients were sprayed at fortnightly intervals. To induce stress conditions caused by the deficiency of either zinc, boron, or both, no applications of these micronutrients were made in certain treatments. This experimental strategy ultimately reflected in the leaf zinc and boron content of the papaya seedlings, which is proportionately correlated with physiological and metabolic responses to stress.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Recording observations\u003c/h2\u003e \u003cp\u003eThe present experiment has included measurements of various plants physiological aspects and biochemical parameters related to different metabolic processes are as follows:\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1. Determination of chlorophyll\u003c/h2\u003e \u003cp\u003eDimethyl sulfoxide (DMSO) solvent was used to extract leaf chlorophyll after cutting the leaves in smaller pieces and placed in test tubes containing 10 ml of solvent, then incubated at 60\u0026ndash;65\u0026ordm;C for one hour. Leaf tissue was cut into. Subsequently the samples were cooled to room temperature for 30 minutes, filtered and absorption measured at 665 nm and 648 nm being the final stages using DMSO as standard with LABMAN double beam UV-Visible spectrophotometer (LMSPUV 1200) (Sadasivam and Manickam, 1992). Chlorophyll concentration (a, b and total) was expressed as mg/g fresh weight and determined by the following formula (Barnes et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1992\u003c/span\u003e):\u003c/p\u003e \u003cp\u003eChlorophyll a (mg/g F.W) = (14.85 A\u003csub\u003e665\u003c/sub\u003e -5.14 A\u003csub\u003e648\u003c/sub\u003e);\u003c/p\u003e \u003cp\u003eChlorophyll b (mg/g F.W) = (25.48 A\u003csub\u003e665\u003c/sub\u003e \u0026ndash; 7.36 A\u003csub\u003e648\u003c/sub\u003e);\u003c/p\u003e \u003cp\u003eTotal chlorophyll (mg/g F.W) = (7.49 A\u003csub\u003e665\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;20.34 A\u003csub\u003e648\u003c/sub\u003e);\u003c/p\u003e \u003cp\u003ewhere: A\u003csub\u003e665\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;absorption value at 665 nm, A\u003csub\u003e648\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;absorption value at 648 nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2. Stomatal density\u003c/h2\u003e \u003cp\u003eDetermination of stomatal density was measured by the method described by Hultine and Marshall (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). A thin layer of clear nail polish was applied to both surfaces of leaves collected from papaya plants across all treatments and a strip of clear stick tape was placed over the nail polish and pressed to stick with nail polish properly. Then the sticky tape has been peeled and the nail polish was fully come off with the tape. The tape with leaf impression was then placed on a microscope slide. The impression was placed from the other side of the leaf on the other part of the slide. The impression was then viewed under the microscope (Olympus SZ-61 SET, 6.7-45X, WHSZ 10X, Tokyo, Japan) at 100x or 400x magnification. The stomatal count was divided by the microscope's field of view area to determine stomatal density.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.4.3. Relative water content of leaf\u003c/h2\u003e \u003cp\u003eLeaf discs were sampled (W) from the top-most fully expanded leaves using a sharp cork borer and kept in a pre-weighed airtight vial which was immediately placed in a picnic cooler (approximately 10\u0026deg;C-15\u0026deg;C). Subsequently, the samples were moistened to full turgidity for 3\u0026ndash;4 hours under normal temperature. After hydration, the samples were removed, lightly wiped with filter or tissue paper and immediately weighed (fully turgid weight, TW). The samples were then oven-dried at 80\u0026deg;C for 24 hours and weighed (dry weight, DW). The relative water content of leaf was calculated with the following formula (Barr and Weatherley \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1962\u003c/span\u003e):\u003c/p\u003e \u003cp\u003eRWC (%) = [(W-DW) / (TW-DW)] x 100,\u003c/p\u003e \u003cp\u003ewhere, W\u0026thinsp;=\u0026thinsp;Sample fresh weight, TW\u0026thinsp;=\u0026thinsp;Sample turgid weight and DW\u0026thinsp;=\u0026thinsp;Sample dry weight.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.4.4. Soluble sugar content\u003c/h2\u003e \u003cp\u003e50 ml clarified lead-free filtrate of leaf sample was taken in a 100 ml volumetric flask 5 ml of concentrated HCl and left for 24 hours at room temperature. The solution was subsequently neutralized first with concentrated NaOH solution, followed by 0.1N NaOH, using phenolphthalein as the endpoint indicator. Titration was done against Fehling's solution similar to the procedure of reducing sugars, thetotal sugar was determined as invert sugars (Lane and Eynon \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1923\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.4.5. Proline content\u003c/h2\u003e \u003cp\u003e25 mg proline (Sigma Aldrich) dissolved to 250 ml as stock solution and standard samples were prepared (1, 2, 3, 4, 5, and 6 \u0026micro;gml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e proline). For each sample, spectrophotometric absorbance with LABMAN double beam UV-Visible spectrophotometer (LMSPUV 1200) was quantified using approximately 1 g tissue at 520 nm, according to the ninhydrin method (Bates et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1973\u003c/span\u003e). Subsequently, the proline content was derived from the standard curve prepared from known concentrations of the amino acids.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.4.6. Super oxide dismutase activity (SOD)\u003c/h2\u003e \u003cp\u003eActivity of SOD has been determined using a biochemical method where xanthine-xanthine oxidase generates O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, and nitroblue tetrazolium (NBT) reduction serves as an indicator of O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e production. SOD and NBT both reacts with O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e. the percent inhibition of NBT reduction is a measure of the amount of SOD present (Oberley and Spitz \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Spitz and Oberley \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). Catalase was included to remove H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e produced by SOD.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e2.4.7. Phenol content\u003c/h2\u003e \u003cp\u003eThe total phenolic contents of the ethanolic extract of papaya leaves were determined using the FolinCiocalteau reagent (Singleton and Rossi \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e1965\u003c/span\u003e) plotting the calibration curve by mixing 1 ml of Gallic acid solutions of different increasing concentrations with 5.0 ml of FolinCiocalteu reagent and 4.0 ml of sodium carbonate solution. Absorbance was measured after 30 minutes at 765 nm. A separate mixture of 1 ml of ethanolic extract (1 g/100 ml) with the same reagents was prepared and optical density was measured after 1 hour to calculate the total phenolic content.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e2.4.8. Antioxidation capacity\u003c/h2\u003e \u003cp\u003eThe total antioxidant capacity (TAC) of samples was derived following the method described by Prieto et al. (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Samples or standards at different concentrations (12.5\u0026ndash;150 \u0026micro;g/mL) were mixed with a reaction mixture containing 0.6 M sulfuric acid, 28 mM sodium phosphate, and 1% ammonium molybdate in test tubes which was incubated at 95\u0026deg;C for 10 minutes to complete the reaction. Absorbance was noted at 695 nm using a spectrophotometer against blank solution. Increased optical density value of the reaction mixture indicates higher total antioxidant capacity, assuming that this concentration range is suitable for accurate calculations of IC\u003csub\u003e50\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e2.4.9. Lipid peroxidation (malondialdehyde or MDA content)\u003c/h2\u003e \u003cp\u003eMDA content determination was conducted following the method of Velikova et al. (\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) with some modifications. Fresh leaves (0.5 g) were ground with 5 mL of 0.1% trichloroacetic acid (TCA) and the extract was centrifuged (14,000 rpm for 5 minutes). 1 ml of supernatant was mixed with 4.5 ml of 0.5% thiobarbituric acid (TBA) and heated in a boiling water bath for 30 min. Reaction was stopped by cooling on ice. Absorbance was detected with three replications at 532 and 600 nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e2.4.10. Leaf zinc content\u003c/h2\u003e \u003cp\u003eLeaf zinc content in papaya has been by the method of Koscielniak et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Papaya leaves were washed, dried, grounded and mixed with a mixture of nitric acid and perchloric acid for digestion for complete release of zinc ions from the sample. The filtered solution was appropriately diluted within the calibration range of the Atomic Absorption Spectrometer (PerkinElmer Model-PINAACLE 900T, Germany), where a hollow cathode lamp emitted light at a specific wavelength (excitation wavelength and emission wavelength from 390 nm to 394 nm and from 540 to 550 nm respectively) absorbed by zinc atoms. The extent of absorption is proportional to the zinc concentration, allowing for quantitative analysis. A calibration curve with known zinc standards is used to quantify the zinc content in the plant sample.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e2.4.11. Leaf boron content\u003c/h2\u003e \u003cp\u003eThe Azomethane H method for boron determination in leaves of papaya plants under the present study included digestion samples with sulfuric acid (concentrated), followed by treatment with Azomethane H and hydrogen peroxide. This forms a yellow complex with boron, enabling precise measurement through spectrophotometry (Spencer and Erdman 1979). An azomethine H derivative (the yellow complex) is considered as spectrophotometric reagent for boron, as compared with azomethine H as blank and maximum absorption is recordedat 425 nm in double beam UV-Visible spectrophotometer (Labman, LMSPUV1900).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e2.5.Statistical analyses\u003c/h2\u003e \u003cp\u003eThe data were statistically analysed with ANOVA and Fisher\u0026rsquo;s least significant differences (LSD) at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 were used to differentiate the treatment means with IBM SPSS Statistics (Version 26.0). The differences among the treatments were tested with critical difference (CD) value at a significance level of 5%, as recommended by Gomez and Gomez (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1984\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eThe physiological and metabolic response to stress in papaya seedlings was notably affected by foliar application of varying doses of zinc and boron in the current experiment. Detailed discussions and interpretations of the mean data on various parameters are provided below:\u003c/p\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Leaf chlorophyll content\u003c/h2\u003e \u003cp\u003e \u003cb\u003eChlorophyll a: Foliar zinc and boron a\u003c/b\u003epplication influenced the cholorophyll production in the chloroplasts of the leaves of papaya seedlings (Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Significantly maximum amount of chlorophyll a (196.1 mg/100g) was noted under the treatment T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%). T\u003csub\u003e6\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.4%) also contained a good amount of chlorophyll a (169.2mg/100g). On the other hand T\u003csub\u003e9\u003c/sub\u003e or control treatment (no application of zinc and boron) has exhibited significantly minimum chlorophyll a content (130.6 mg/100g). \u003cb\u003eChllorophyll b\u003c/b\u003e: In the present experiment maximum amount of chlorophyll b (69.0 mg/100g0 was noted under treatment T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%) which was statistically in line with the plants under the treatment T\u003csub\u003e6\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.4%) with 62.7 mg/100g chlorophyll b content (Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). \u003cb\u003eTotal chlorophyll\u003c/b\u003e: Foliar application of zinc and boron and their combinations also influenced the total chlorophyll content of papaya seedlings in our study (Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The maximum amount of total chlorophyll (265.1mg/100g) in the papaya leaves has been observed under T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%) as significantly maximum which was indifferent with the total chlorophyll content in the papaya plants under the treatment T\u003csub\u003e5\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.2%). Significantly lowest amount of total chlorophyll (176.8 mg/100g) was noted under T\u003csub\u003e9\u003c/sub\u003e or control treatment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Stomatal density\u003c/h2\u003e \u003cp\u003eFoliar application of zinc and boron and their combination has greatly influenced the stomatal density of papaya leaves in the present study(Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).Papaya leaves exhibited significantly maximum density of stomata (657.4 per mm\u003csup\u003e2\u003c/sup\u003e leaf area) under the treatment T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%) and it was statistically similar in the plants of the treatment T\u003csub\u003e6\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.4%) with a value of 635.6 numbers of stomata per mm\u003csup\u003e2\u003c/sup\u003e leaf area. Increased doss of zinc sulphate as well as borax has also increased the stomatal density. On contrary, significantly minimum stomatal density (422.6 per mm\u003csup\u003e2\u003c/sup\u003e leaf area) has been noted in the control treatment (T\u003csub\u003e9\u003c/sub\u003e) under the deficiency of zinc and boron which indicated the stressfulness of the papaya seedlings.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Relative water content in leaves\u003c/h2\u003e \u003cp\u003eRelative water content in leaves in a certain condition indicates the water availability of the plants for its physiological process particularly the photosynthesis. Present experiment exhibited maximum relative water content of papaya leaves (Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) showed maximum physiological activity under treatment combination T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%) with significantly highest relative water content (87.3%). The control treatment (T\u003csub\u003e9\u003c/sub\u003e) has shown the minimum relative water content in leaves (71.2%) indicating the lowest physiological availability of water and thus in stress condition and treatment T\u003csub\u003e1\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2%) has not exhibited any difference with T\u003csub\u003e9\u003c/sub\u003e with regard to relative water content of leaf.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Soluble sugar content\u003c/h2\u003e \u003cp\u003eThe photosynthates in form of soluble sugar in leaves are the clear indicator of photosynthetic activity of the plants which depends upon the chlorophyll content, stomatal density and relative water content in leaves. The leaves having high chlorophyll content, good stomatal density and higher relative water content, always stands for greater photosynthates. The findings of the current research revealed that the application of zinc and boron has greatly influenced the photosynthetic rate (Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Maximum photosynthates in form of soluble sugar (75.6mg/g) was noted in the treatment T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%) having good amount of zinc and boron. Other treatments with adequate zinc and boron application have also exhibited significant amount of soluble sugar. Being stressed condition in the treatment T\u003csub\u003e9\u003c/sub\u003e or control having no zinc and boron, the plants produced significantly minimum amount of soluble sugar (42.7mg/g) being under less photosynthetic activity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Leaf proline content\u003c/h2\u003e \u003cp\u003eProline accumulation occurs in plant parts under stressful conditions caused by various abiotic and biotic factors, including adverse environmental conditions, nutrient deficiencies, and mineral toxicity. It is also reported as measure of osmolite to mitigate oxidative stress by scavenging reactive oxygen species. In the current research, the proline content of papaya leaves varied significantly along the application of varying doses of zinc and boro (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Increased doses of zinc and boron resulted decrease in leaf proline content in papaya leaves. Application of ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.2% (T\u003csub\u003e7\u003c/sub\u003e) has recorded proline of 22.1 \u0026micro;mole/g fresh weight which was lowest and statistically indifferent with T\u003csub\u003e8\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.4%) which exhibited proline content 23.1 \u0026micro;mole/g fresh weight. Significantly maximum leaf proline content (45.2 \u0026micro;mole/g fresh weight) was noticed under control or no application of zinc and boron which indicated the stressed condition of papaya seedlings under micronutrient deficiency and on contrary comfort situation of plants under T\u003csub\u003e7\u003c/sub\u003e and T\u003csub\u003e8\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Superoxide dismutase (SOD)\u003c/h2\u003e \u003cp\u003eSuperoxide dismutase is an enzyme that facilitates the dismutation of superoxide radicals produced within the plant system under stress conditions. This process converts superoxides into non-reactive oxygen molecules and peroxide, thereby preventing oxidative damage to plant cell parts and organelles. Plants increase their production of SOD in response to stress conditions to mitigate oxidative damage. The findings of the current research indicates that the SOD production have been decreased with increasing doses or in the absence of zinc and boron (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) led the plants under greater stress as indicated by significantly highest SOD content (36.5 unit/mg) under control treatment (T\u003csub\u003e9\u003c/sub\u003e). On the other hand lowest SOD activity (15.8 unit/mg) has been recorded under T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.2%) and it was closely set by T\u003csub\u003e8\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.4%) with SOD activity of 18.4 unit/mg.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section2\"\u003e \u003ch2\u003e3.7. Leaf total phenol\u003c/h2\u003e \u003cp\u003eVarious phenolic compounds have the potential to effectively scavenge harmful reactive oxygen species. The phenyl propanoid biosynthetic pathway is activated under different plant stress conditions, leading to the accumulation of various types of phenols in plants. Papaya seedlings under control treatment (T\u003csub\u003e9\u003c/sub\u003e) has produced a considerable highest amount of phenol (43.7 mgGAE/100g) while on contrary T\u003csub\u003e8\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.4%) and T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.2%) has exhibited lower quantity of phenol in papaya leaves as 18.2 and 21.5 mgGAE/100g respectively(Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Thus the plants under control treatment with no micronutrient application were under stress condition and in other treatments of zinc and boron application they were in comfort.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section2\"\u003e \u003ch2\u003e3.8. Antioxidation capacity (DPPH radical scavenging %)\u003c/h2\u003e \u003cp\u003eUnder biotic and abiotic stress conditions, plants experience increased production of reactive oxygen species (ROS), causes oxidative stress induction. Plants inherently possess the capacity to synthesize non-enzymatic antioxidants under normal conditions, which counter the oxidative stress of ROS (Wang et al., \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Xu et al., \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2003\u003c/span\u003e and Kayihan et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The findings of the current study revealed that the foliar application of zinc and boron in sufficient quantity resulted the higher antioxidant production (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) reflected by significant maximum under T\u003csub\u003e8\u003c/sub\u003e(ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.4%) i.e. 76.6% DPPH radical scavenging and it was statistically alike with T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.2%) and showed 73.1% DPPH radical scavenging. On contrary, the control treatment (T\u003csub\u003e9\u003c/sub\u003e) has exhibited lowest antioxidation capacity (58.7% DPPH radical scavenging) and it was similar with T\u003csub\u003e1\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2%, recorded 62.7% DPPH radical scavenging).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec28\" class=\"Section2\"\u003e \u003ch2\u003e3.9. Lipid peroxidation (MDA content)\u003c/h2\u003e \u003cp\u003eLipid peroxidation is a deleterious process in plants. It affects membrane properties, causes protein degradation and limits the capacity of ionic transport due to high, ultimately triggering the cell death process. The production of ROS in greater quantity causes more lipid peroxidation which is detected by greater quantity of MDA as it is the final product of peroxidation of polyunsaturated fatty acids in the cells. The findings of the present research exhibited the significantly maximum lipid peroxidation (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) was taken place in the papaya plants under control treatment (T\u003csub\u003e9\u003c/sub\u003e) and that was indicated by highest MDA content of leaves (67.4 \u0026micro; mole/g FW). Significantly lowest MDA content was recorded in the plants under T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.2%) i.e. 34.0 \u0026micro; mole/g FW. The other micronutrient treatments also exhibited lower MDA content in the papaya leaves that ranged up to 46.6 \u0026micro; mole/g FW.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec29\" class=\"Section2\"\u003e \u003ch2\u003e3.10. Leaf zinc and boron content\u003c/h2\u003e \u003cp\u003eZinc accumulation in the leaves of papaya seedlings have been significantly varied within the treatment combinations in the present experiment (Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Maximum zinc content in papaya leaves (22.2 \u0026micro;g/g dry leaf) was noted in T\u003csub\u003e8\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.4%) which was in line with T\u003csub\u003e7\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.2%) (21.6 \u0026micro;g/g dry leaf) and T\u003csub\u003e2\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4%) (21.4 \u0026micro;g/g dry leaf).In all these cases application of zinc was done in highest concentration. Significantly lowest leaf zinc content (12.1 \u0026micro;g/g dry leaf) was noted in the plants under control treatment (T\u003csub\u003e9\u003c/sub\u003e) having no zinc application.\u003c/p\u003e \u003cp\u003eHighest boron content (17.1\u0026micro;g/g dry leaf) has been found in T\u003csub\u003e8\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% with Borax @ 0.4%) which was statistically in line with T\u003csub\u003e4\u003c/sub\u003e(Borax @ 0.4%) and T\u003csub\u003e6\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.4%) with boron content of 17.0 and 16.7\u0026micro;g/g dry leaf respectively(Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). In all these treatments application of boron was in highest concentration. Control treatment (T\u003csub\u003e9\u003c/sub\u003e) exhibited lowest amount of boron (6.8\u0026micro;g/g dry leaf) in the papaya leaves as there was no boron application and that was statistically similar with T\u003csub\u003e1\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2%) and T\u003csub\u003e2\u003c/sub\u003e (ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4%) having no boron application.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003e \u003cb\u003e4.1. Zinc and boron deficiency caused stress in the papaya seedlings that induced chlorosis, reduced stomatal density, relative water content in leaf and photosynthesis\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe combined application of zinc and boron increased different types and total chlorophyll levels in papaya plants, as observed in this experiment. Plants that were deficient in zinc and boron, without these micronutrients, showed chlorophyll deficiency or chlorotic symptoms. Under severe zinc and boron stress, some plants exhibited chlorosis and necrosis symptoms. Borowiak et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) demonstrated increased photosynthetic activity in Salix hybrid due to higher leaf chlorophyll content with zinc treatment. Jain et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) observed chlorophyll destruction due to oxidative damage caused by zinc deficiency in sugarcane. Xu et al. (\u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) and Baycu et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) reported oxidative degradation of chlorophyll pigments under zinc deficiency conditions.\u003c/p\u003e \u003cp\u003eHigher concentrations of zinc and boron improved stomatal density in papaya leaves likely due to proper leaf development and reduced stress resulting from adequate nutrient levels in this experiment. Tufail et al. (\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) found greater stability of leaf cell membranes and increased stomatal density of rice seedlings with sufficient zinc nutrition under salinity stress. Yin et al. (\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) reported lower stomatal density in Neolamarckia under boron deficiency. Liu et al. (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) observed lower stomatal density and deformed stomata in trifoliate orange rootstock under boron and zinc deficiency conditions.\u003c/p\u003e \u003cp\u003ePapaya plants treated with sufficient zinc and boron exhibited higher relative water content of leaves in treatment T\u003csub\u003e7\u003c/sub\u003e (ZnSO4 @ 0.4% + Borax @ 0.2%), indicating better physiological conditions compared to plants under the control treatment. Hernandez and Almansa (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) reported reduced relative water content in pea leaves under stress conditions. Luis et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) observed lower leaf relative water content in tomato plants under boron deficiency and toxicity conditions. Similar findings were reported in safflower by Sulus and Leblebici (\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Jabeen and Ahmad (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012a\u003c/span\u003e) found increased relative water content in sunflower and safflower leaves with foliar application of zinc and boron, reducing stress.\u003c/p\u003e \u003cp\u003eTreatment T\u003csub\u003e7\u003c/sub\u003e (ZnSO4 @ 0.4% + Borax @ 0.2%) evidenced the highest chlorophyll content, stomatal density, and relative water content in papaya leaves, potentially contributing to increased photosynthetic activity and higher soluble sugar production as photosynthates. Adequate nutrition of zinc and boron in papaya facilitated significant chlorophyll production and protected against oxidation. Shokat et al. (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) reported increased sugar synthesis and higher yield in wheat grown under drought with micronutrient application, including zinc and boron. Xu et al. (\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) noted reduced photosynthesis and sugar production in alfalfa under various stresses, including nutritional stress.\u003c/p\u003e \u003cp\u003e \u003cb\u003e4.2. Zinc and boron deficiency in papaya seedlings resulted activation of cellular stress mitigation strategies like higher proline, SOD, phenols, antioxidants etc.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eHigher proline content in plants under the control treatment (deficient in zinc and boron) indicated maximum stress, whereas proper application of zinc and boron together resulted in lower proline levels in the leaves. The increased proline accumulation was a response to cope with stress caused by micronutrient deficiency in this experiment. Sultana et al. (\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) observed reduced proline content in wheat under stress conditions after zinc application. Conversely, Yang et al. (\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) found higher proline content in zinc-deficient tobacco plants.\u003c/p\u003e \u003cp\u003ePlants under the control treatment exhibited higher production of superoxide radicals, leading to increased levels of superoxide dismutase (SOD) for dismutation activity to mitigate stress effects. In contrast, papaya plants with adequate zinc and boron nutrition showed lower SOD content in their leaves. Song et al. (\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) reported increased SOD content in beet under boron-induced oxidative stress. Kakmak (2000) and Hasanuzzaman et al. (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) observed higher SOD production to reduce ROS concentration under zinc deficiency in plants. Foyer (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and Mittler (2022) highlighted the positive role of zinc and boron in regulating ROS signalling responses in plants under stress. Choudhary et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) found oxidative damage indicated by higher SOD content in Mentha and Cymbopogon under zinc and boron stress.\u003c/p\u003e \u003cp\u003eUnder stress conditions caused by zinc and boron deficiency in the present research, higher production of total phenols was observed in plants under the control treatment to scavenge the reactive oxygen species produced. Conversely, proper zinc and boron nutrition resulted in lower production of leaf phenols. It has been described that zinc deficiency stress increases phenolic content of many plants grown under adverse weather conditions by activating phenyl propanoid biosynthetic pathways (Hassan et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Hammerschmitt et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Ann et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Golkar (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) found increased phenolic content in safflower leaves under micronutrient and salinity stress.\u003c/p\u003e \u003cp\u003eProper nutrition of papaya plants with zinc and boron application in this experiment resulted in higher antioxidation capacity, whereas deficient plants exhibited lower capacity to scavenge reactive oxygen species (ROS). Noreen et al. (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) observed improved antioxidation capacity in barley with foliar zinc application. Similarly, Zoufan et al. (\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) reported enhanced antioxidation capacity and reduced oxidative damage in Chenopodium murale L. plants exposed to elevated zinc levels. Kayihan et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) found higher antioxidation capacity in Arabidopsis with boron application, and Wang et al. (\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) observed similar results in rapeseed seedlings.\u003c/p\u003e \u003cdiv id=\"Sec31\" class=\"Section2\"\u003e \u003ch2\u003e4.3. Cellular damage in papaya seedlings caused due to zinc and born deficiency\u003c/h2\u003e \u003cp\u003eLipid molecules in cell membranes, as well as unit membranes of other cell organelles, are highly susceptible to peroxidation, which leads to the production of malondialdehyde (MDA) and ultimately results in membrane damage, leakage, and loss of stability (John and Steven \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1978\u003c/span\u003e). In the present experiment, papaya plants without application of zinc and boron (T9: control) exhibited higher lipid peroxidation rates and consequently higher MDA production due to physiological stress. Conversely, plants receiving proper zinc and boron application (T8: ZnSO4 @ 0.4% with Borax @ 0.4% and T7: ZnSO4 @ 0.4% with Borax @ 0.2%) may have been in a more comfortable physiological condition, resulting in lower lipid peroxidation (Marichali et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Chen et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) observed higher MDA content in alfalfa under copper and zinc stress, consistent with findings by Jabeen and Ahmad (2012) in sunflower and safflower, and Shah et al. (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) in Citrange.\u003c/p\u003e \u003cp\u003eNormal ranges of zinc and boron content in papaya leaves have been published as 21.2 to 22.4 \u0026micro;g/g dry leaf and 16.1 to 17.3 \u0026micro;g/g dry leaf or more, respectively (Subedi et al. \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Nautiyal et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). Under deficiency conditions, zinc and boron content were noted to decrease to 11 to 13 \u0026micro;g/g dry leaf and 6.4 to 7.0 \u0026micro;g/g dry leaf or less, respectively (Vasanthu et al. \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Zinc deficiency was prominent in the control treatment (T9) as well as treatments T3 and T4, which received no zinc application. Similarly, boron deficiency was observed in the control treatment (T\u003csub\u003e9\u003c/sub\u003e) as well as treatments T1 and T2, which received no boron application. Deficiencies of zinc and boron caused nutrient stress conditions in papaya seedlings, supported by quantification of antioxidative enzymes (SOD), proline, phenol production, and lipid peroxidation.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn conclusion, the findings of the present experiment revealed the significant contribution of foliar application of zinc and boron on papaya seedlings particularly in physiological and metabolic processes.\u0026nbsp;The application of zinc sulphate @ 0.4% along with borax @ 0.2% promoted the production of leaf chlorophyll (a, b and total) and thereby increased photosynthates (soluble sugar) along with greater relative water content in leaves available for all metabolic processes. Increased zinc and boron application also minimized the expression of stress in the papaya seedlings by reducing the proline content, superoxide dismutase enzyme as well as phenol content. The rate of lipid peroxidation in leaves was also minimized with higher rate of zinc application along with moderate boron application which was indicated by lower malondialdehyde content. \u0026nbsp;Thus the research provides a proof that the papaya seedlings experienced stressed condition under deficiency of zinc and boron which is evident from stress mitigation strategies adopted by the plants under no application of zinc and boron with respect to physiological and cellular metabolic processes. Additionally, this stress condition can be overcome by the foliar application of zinc sulphate @ 0.4% and borax @ 0.2% which is beneficial for better seedling growth of papaya with respect to less stress and high metabolic activity.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePrahlad Deb:\u003c/strong\u003e Writing \u0026ndash; review \u0026amp; editing, Validation, Supervision, Resources, Project administration, Investigation, Conceptualization. \u003cstrong\u003eKumar Abhishek:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; original draft, Visualization, Methodology, Formal analysis, Data curation. \u003cstrong\u003ePayel Das:\u003c/strong\u003e Methodology, Formal analysis, Data curation\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank all the academic, research and administrative staffs of Visva-Bharati University for all kind of support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDisclosure statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo fund from external Govt. or Non-Govt. funding agencies has been received for the present research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eORCID\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePrahlad Deb: https://orcid.org/0000-0003-0725-7776\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAnn C, Jaco V, Herman C (2001) The redox status of plant cells (AsA and GSH) is sensitive to zinc imposed oxidative stress in roots and primary leaves of \u003cem\u003ePhaseolus vulgaris\u003c/em\u003e. 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Chemosph75: 1468\u0026ndash;1476. http://doi.org/10.1016/j.chemosphere.2009.02.033\u003c/li\u003e\n \u003cli\u003eWang X, Song B, Wu Z, Zhao X, Song X, Adil FM, Riaz M, Lal MK, Huang W (2023) Insights into physiological and molecular mechanisms underlying efficient utilization of boron in different boron efficient \u003cem\u003eBeta vulgaris\u003c/em\u003e L. varieties. Plant Physiol. Biochem 197: 107619. https://doi.org/10.1016/j.plaphy.2023.02.049\u003c/li\u003e\n \u003cli\u003eXu HY, Tong ZY, He F, Li XL (2020) Response of alfalfa (\u003cem\u003eMedicago sativa\u003c/em\u003e L. to abrupt chilling as reflected by changes in freezing tolerance and soluble sugars. Agron10(2): 255. http://doi.org/10.3390/agronomy10020255\u003c/li\u003e\n \u003cli\u003eXu Q, Shi G, Zhou H (2003) Chlorophyll content and active oxygen scavenging system of chlorophyll content before water wheeling by Cd and Zn combined pollution Influence. J Ecol1(22): 5-8.\u003c/li\u003e\n \u003cli\u003eYang FW, Zhang HB, Wang Y, He GQ, Wang JC, Guo DD, Li T, Sun GY, Zhang HH (2021) The role of antioxidant mechanism in photosynthesis under heavy metals Cd or Zn exposure in tobacco leaves. J Plant Inter 16(1): 354\u0026ndash;366. https://doi.org/10.1080/17429145.2021.1961886\u003c/li\u003e\n \u003cli\u003eYin Q, Kang L, Liu Y, Qaseem MF, Qin W, Liu T, Li H, Deng X, Wu A (2022) Boron deficiency disorders the cell wall in Neolamarckiacadamba. Indust Crops Prod176(46): 114332.http://doi.org/10.1016/j.indcrop.2021.114332\u003c/li\u003e\n \u003cli\u003eZoufan P, Karimiafshar A, Shokati S, Hassibi P, Rastegarzadeh S (2018) Oxidative damage and antioxidant response in \u003cem\u003eChenopodium murale\u0026nbsp;\u003c/em\u003eL. exposed to elevated levels of Zn. Braz Arch Biol Tech61: e18160758. http://doi.org/10.1590/1678-4324-2018160758\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1: Leaf chlorophyll content, stomatal density, relative leaf water content and soluble sugar content of papaya seedlings as influenced by foliar application of zinc and boron at 90\u003csup\u003eth\u003c/sup\u003e day\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"103%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTreatments\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eChlorophyll a content (mg/100g FW)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eChlorophyll b content (mg/100g FW)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal chlorophyll content (mg/100g FW)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eStomatal density (per mm\u003csup\u003e2\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRelative Leaf Water Content (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSoluble sugar content (mg/g)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e142.6\u0026plusmn;5.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e56.1\u0026plusmn;4.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e198.7\u0026plusmn;7.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e587.6\u0026plusmn;27.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e75.0\u0026plusmn;4.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e46.8\u0026plusmn;3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e152.7\u0026plusmn;7.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e53.7\u0026plusmn;4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e206.4\u0026plusmn;9.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e610.9\u0026plusmn;28.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e77.5\u0026plusmn;4.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e48.2\u0026plusmn;4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e153.6\u0026plusmn;6.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e56.9\u0026plusmn;5.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e210.5\u0026plusmn;8.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e591.2\u0026plusmn;16.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e79.3\u0026plusmn;5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e47.0\u0026plusmn;3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e148.7\u0026plusmn;8.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e52.3\u0026plusmn;4.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e201.0\u0026plusmn;7.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e598.5\u0026plusmn;22.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e81.1\u0026plusmn;7.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e58.5\u0026plusmn;4.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e175.8\u0026plusmn;6.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e61.8\u0026plusmn;6.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e237.6\u0026plusmn;8.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e641.8\u0026plusmn;18.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e82.6\u0026plusmn;6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e63.4\u0026plusmn;5.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e169.2\u0026plusmn;7.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e62.7\u0026plusmn;5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e231.9\u0026plusmn;7.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e635.6\u0026plusmn;24.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e81.6\u0026plusmn;7.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e68.9\u0026plusmn;4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e196.1\u0026plusmn;9.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e69.0\u0026plusmn;6.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e265.1\u0026plusmn;9.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e657.4\u0026plusmn;19.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e87.3\u0026plusmn;6.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e75.6\u0026plusmn;6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e153.5\u0026plusmn;5.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e56.9\u0026plusmn;5.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e210.4\u0026plusmn;9.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e609.2\u0026plusmn;15.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e80.7\u0026plusmn;5.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e65.2\u0026plusmn;6.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e130.6\u0026plusmn;7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e46.2\u0026plusmn;4.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e176.8\u0026plusmn;6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e422.6\u0026plusmn;14.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e71.2\u0026plusmn;5.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e42.7\u0026plusmn;5.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSE(m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e3.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e5.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e5.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e1.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e2.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCD(0.05)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e11.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e7.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e16.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e15.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e5.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 13px;\"\u003e\n \u003cp\u003e7.54\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eT\u003csub\u003e1\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2%, \u003cstrong\u003eT\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e :ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4%, \u003cstrong\u003eT\u003csub\u003e3\u003c/sub\u003e\u003c/strong\u003e : Borax @ 0.2%, \u003cstrong\u003eT\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e :Borax @ 0.4%, \u003cstrong\u003eT\u003csub\u003e5\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.2%, \u003cstrong\u003eT\u003csub\u003e6\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.4%, \u003cstrong\u003eT\u003csub\u003e7\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%, \u003cstrong\u003eT\u003csub\u003e8\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.4%, \u003cstrong\u003eT\u003csub\u003e9\u003c/sub\u003e\u003c/strong\u003e (Control)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2: Physio-metabolic expression of papaya seedlings and leaf zinc and boron as influenced by foliar application of zinc and boron at 90\u003csup\u003eth\u003c/sup\u003e day\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"108%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTreatments\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLeaf proline content (\u0026micro; mole/g FW)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSuperoxide dismutase \u0026nbsp;(SOD) unit/mg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhenol (mgGAE/100g)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAntioxidation capacity (DPPH radical scavenging %)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLipid peroxidation (MDA)\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(\u0026micro; mole/g FW)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eZinc content in leaves\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(\u0026micro;g/g dry weight)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBoron content in leaves\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(\u0026micro;g/g dry weight)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e31.5\u0026plusmn;2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e27.4\u0026plusmn;2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e31.3\u0026plusmn;4.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e62.7\u0026plusmn;5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e46.6\u0026plusmn;3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e17.3\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e7.1\u0026plusmn;0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e30.2\u0026plusmn;3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e22.1\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e30.8\u0026plusmn;3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e69.2\u0026plusmn;5.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e42.2\u0026plusmn;4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e21.4\u0026plusmn;2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e6.9\u0026plusmn;0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e29.3\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e29.5\u0026plusmn;3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e38.4\u0026plusmn;3.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e59.8\u0026plusmn;5.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e41.6\u0026plusmn;5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e12.6\u0026plusmn;1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e12.5\u0026plusmn;1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e28.6\u0026plusmn;2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e26.3\u0026plusmn;3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e35.1\u0026plusmn;3.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e61.3\u0026plusmn;5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e39.1\u0026plusmn;3.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e13.0\u0026plusmn;1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e17.0\u0026plusmn;1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e26.3\u0026plusmn;3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e21.7\u0026plusmn;2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e26.7\u0026plusmn;2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e66.4\u0026plusmn;6.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e40.5\u0026plusmn;3.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e18.0\u0026plusmn;1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e11.9\u0026plusmn;1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e24.4\u0026plusmn;2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e20.2\u0026plusmn;2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e24.5\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e68.2\u0026plusmn;6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e39.3\u0026plusmn;2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e17.8\u0026plusmn;1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e16.7\u0026plusmn;1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e22.1\u0026plusmn;3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e15.8\u0026plusmn;1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e21.5\u0026plusmn;2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e73.1\u0026plusmn;6.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e34.0\u0026plusmn;4.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e21.6\u0026plusmn;1.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e12.4\u0026plusmn;1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e23.1\u0026plusmn;3.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e18.4\u0026plusmn;2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e18.2\u0026plusmn;2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e76.6\u0026plusmn;5.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e39.8\u0026plusmn;4.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e22.2\u0026plusmn;1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e17.1\u0026plusmn;1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eT9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e45.2\u0026plusmn;3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e36.5\u0026plusmn;4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e43.7\u0026plusmn;3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e58.7\u0026plusmn;6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e67.4\u0026plusmn;5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e12.1\u0026plusmn;1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e6.8\u0026plusmn;0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSE(m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e0.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 11px;\"\u003e\n \u003cp\u003e1.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14px;\"\u003e\n \u003cp\u003e2.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e1.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 15px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCD(0.05)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n 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:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4%, \u003cstrong\u003eT\u003csub\u003e3\u003c/sub\u003e\u003c/strong\u003e : Borax @ 0.2%, \u003cstrong\u003eT\u003csub\u003e4\u003c/sub\u003e\u003c/strong\u003e :Borax @ 0.4%, \u003cstrong\u003eT\u003csub\u003e5\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.2%, \u003cstrong\u003eT\u003csub\u003e6\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.2% + Borax @ 0.4%, \u003cstrong\u003eT\u003csub\u003e7\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.2%, \u003cstrong\u003eT\u003csub\u003e8\u003c/sub\u003e\u003c/strong\u003e:ZnSO\u003csub\u003e4\u003c/sub\u003e @ 0.4% + Borax @ 0.4%, \u003cstrong\u003eT\u003csub\u003e9\u003c/sub\u003e\u003c/strong\u003e (Control).\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Visva-Bharati University","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Zinc, boron, papaya seedlings, SOD, proline, MDA, phenol","lastPublishedDoi":"10.21203/rs.3.rs-5890450/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5890450/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePapaya is among the most important tropical fruits and is cultivated in nearly all Indian states. Micronutrient deficiency at an early stage can lead to poor growth and reduced yield in papaya. The effect of foliar application of zinc and boron on stress metabolism of papaya seedlings has been studied through a pot experiment conducted under greenhouse conditions. The experiment was framed in a completely randomised design with nine treatments that included zinc sulphate @ 0.2%, 0.4% and borax @ 0.2%, 0.4% and their combinations along with a control treatment (distilled water only). Seedlings were grown in polythene bags filled with properly washed sand and sprayed with the above treatment combinations of micronutrients at 15 days interval after germination adjusting neutral pH. The foliar spray of 0.4% zinc sulphate combined with 0.2% borax led to an increase in leaf chlorophyll content (a, b, and total), thereby boosting photosynthesis (soluble sugars) and enhancing the relative water content in leaves available for all metabolic processes. Increased application of zinc and boron also reduced the stress expression of papaya seedlings by reducing proline content, superoxide dismutase enzyme and phenol content. Lipid peroxidation in the leaf was also minimal with higher zinc application and moderate boron application, as indicated by the lower malondialdehyde content. Therefore, foliar application of 0.4% zinc sulphate and 0.2% borax can be recommended for better seedling growth of papaya in terms of less stress and high metabolic activity.\u003c/p\u003e","manuscriptTitle":"Foliar application of zinc and boron alleviate deficiency stress in papaya (Carica papaya L.) seedlings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-28 08:43:24","doi":"10.21203/rs.3.rs-5890450/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"17a10c70-cf6c-4df6-a4b8-9915ee1aef0d","owner":[],"postedDate":"January 28th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":43329989,"name":"Horticulture"},{"id":43329990,"name":"Plant Physiology and Morphology"}],"tags":[],"updatedAt":"2025-01-28T08:43:24+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-28 08:43:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5890450","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5890450","identity":"rs-5890450","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}