Effects of Exogenous Trehalose on Plant Growth, Physiological and Biochemical Responses in Gardenia jasminoides Seedlings During Cold Stress

Gardenia jasminoides Ellis is an evergreen plant of the genus Gardenia in the Rubiaceae Juss. trehalose (Tre), as a stress metabolite of plants adapted to environmental stress, can enhance the stress resistance of plants and ensure the normal growth and development of crops. In order to explore the effect and mechanism of trehalose on the growth and cold resistance of gardenia seedlings under low temperature stress, this study treated the seedlings with trehalose under different degrees of low temperature stress, observed their growth conditions, and discussed the effects of trehalose on cold resistance of Gardenia from the perspectives of phenotype, photosynthesis, active oxygen species, antioxidant system, endogenous hormones and respiratory metabolic products. To provide a theoretical basis for trehalose to improve cold resistance of plants. The results show that: Low temperature stress at − 3℃ significantly inhibited the growth of Gardenia, while trehalose at 15 mmol/L restored plant height, number of leaves, total plant weight, fresh weight of above ground and underground parts to 88.10%, 81.05%, 98%, 87.61% and 96.68% of the normal temperature conditions at 20℃. The total length of root, number of lateral roots, total root surface area and root volume recovered to 88.48%, 74.08%, 104.03% and 83.77% under normal temperature at 20℃. The chlorophyll content, chlorophyll fluorescence parameters and photosynthetic intensity parameters in leaves of gardenia jasminoides were significantly decreased under low temperature stress at − 3℃, while the contents of chlorophyll a, chlorophyll b and total chlorophyll were significantly increased under 15 mmol/L trehalose treatment (by 90.56%, 45.16% and 74.39%, respectively). Meanwhile, chlorophyll fluorescence parameters (φPSII, Fv '/Fm' and qP increased by 18.60%, 73.17% and 81.82%, respectively) and photosynthetic intensity parameters (Pn, Gs, Ci and Tr increased by 33.33%, 70.86%, 14.83% and 116.50%, respectively) were also increased. At -3℃, trehalose treatment at 15 mmol/L could significantly increase the activities of SOD, POD and CAT in roots of Gardenia (increased by 12.76%, 32.64% and 10.69%, respectively), and reduce the content of reactive oxygen species (H2O2 and superoxide anion radical decreased by 20.49% and 3.39%, respectively). At the same time, the contents of root osmotic regulatory substances (proline and malondialdehyde) were decreased by 15.16% and 12.65%, respectively. At -3℃, trehalose treatment at 15 mmol/L significantly increased root auxin content (32.03%) and significantly decreased trans-zeanoside content (14.92%), but had no significant effects on gibberellin and abscisic acid contents. 15 mmol/L trehalose can also regulate the content of root respiratory metabolites under low temperature stress, and increase malic acid content by 96.77% under -3℃ low temperature stress, while decrease succinic acid content by 56.34%. In conclusion, low temperature stress inhibited the growth of Gardenia. Trehalose could increase chlorophyll content and chlorophyll fluorescence parameters in leaves of Gardenia and enhance photosynthesis to promote the growth of Gardenia. Under low temperature stress, trehalose can reduce the content of active oxygen by improving the antioxidant capacity of roots of gardenia seedlings, so as to reduce the damage of active oxygen, maintain the level of active oxygen metabolism and enhance the cold resistance of plants. Trehalose also enhanced the osmoregulation ability and the stability of cell membrane by reducing the content of root osmoregulation substances, and enhanced the cold resistance of Gardenia by regulating the content of root hormones and aerobic respiratory metabolites.