Kundu, S.; Weerasinghe, M.; Gagne, M.; Long, S.; Minocha, R.; Minocha, S.

Introduction: Polyamines regulate plant growth and development under normal conditions and protect plants from a multitude of biotic and abiotic stresses. However, little information is available about how polyamines improve salt tolerance. Methods: This study was conducted to investigate whether exogenous polyamine application has the potential to maintain poplar growth and yield under a short duration of salt stress. We analyzed the trends in growth and physiological and biochemical responses of hybrid poplar (Populus nigra x maximowiczii, clone NM6) plants to salt stress by foliar application of putrescine (a diamine). Leaves of young greenhouse-grown plants were sprayed with 1 mM putrescine on several days following one-time application of 100 mM and 200 mM NaCl via roots. For measurement of growth, plant height, stem diameter, and leaf number for each plant were recorded throughout the experiment. Studies on the physiological and biochemical trends included gas exchange, total chlorophyll, carotenoids, soluble sugars and proteins, amino acids, polyamines, and relative water content in leaves. Results: Putrescine spray on the salt-treated plants caused a significant increase in chlorophyll a & b, carotenoids, and soluble proteins on a fresh weight basis. 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: In conclusion, the results indicate that putrescine did reverse the effects of salt in many ways, and there were trends indicating that sprayed putrescine promotes salt tolerance in young poplar plants.