Enhancing salt tolerance in a hybrid poplar (Populus nigra x maximowiczii) through exogenous putrescine application: Growth, physiological, and biochemical responses

Introduction Putrescine, a polyamine involved in plant growth and stress responses, has shown potential in mitigating abiotic stress effects. However, little is known about the exogenous addition of putrescine regarding salt tolerance in trees. Methods This study was conducted to investigate whether exogenous putrescine application via foliar spray enhances growth in a hybrid poplar ( Populus nigra x maximowiczii, clone NM6) under a short duration of salt stress. Salt stress was induced by irrigating roots with 100 mM and 200 mM NaCl, followed by foliar spraying of putrescine on several days. Measurement of growth including plant height and stem diameter for each plant were recorded in the greenhouse every 15 days throughout the experiment. Gas exchange, total chlorophyll, carotenoids, soluble sugars and proteins, amino acids, polyamines, and relative water content were analyzed in foliage collected 3, 6, 7, 13, 20, 35 days after treatment. Results Putrescine spray on the salt-treated plants caused a significant increase in plant growth. Putrescine application caused a significant increase in fructose, glucose, and galactose in all plants, but putrescine spray had a variable impact on the sucrose content of 100 mM NaCl-treated plants. Based on metabolic responses, plants treated with 100 mM NaCl fared better when sprayed with putrescine than those treated with 200 mM NaCl. Discussion Exogenous application of putrescine mitigated growth inhibition effects of salinity. These finding highlight the potential of putrescine as a practical approach to increase salt tolerance in young poplar trees, with implications for forestry and land reclamation in saline environment.