Foliar application of exogenous polyamines to ameliorate drought-induced oxidative damage and physiological inhibition in Toona ciliata seedlings

Toona ciliata is a tree species native to Oceania, Southeast Asia, China and to the Indian subcontinent that is favoured for production of very high value timber. In this study, the potential for exogenous application of polyamines (PAs) for improving the ability of young trees to tolerate drought stress was examined. Two-year-old seedling trees were treated with foliar sprays of three PAs (putrescine (Put), spermidine (Spd) and spermine (Spm)) in 1 mM solutions three times at intervals of one day and then exposed to drought stress by withholding of irrigation over a period of 21 days. The PA pre-treatments reduced water loss and improved membrane integrity, photosynthetic capacity, antioxidant systems and upregulation of the expression of S-adenosylmethionine decarboylase (SAMDC) gene of trees under drought stress, with Spd or Spm pre-treatments generally being superior to that of Put. The enhanced drought tolerance of young T. ciliata seedlings induced by PA pre-treatment was associated with enhanced photosynthetic capacity, and a reduction in the loss of water in association with altered anatomical structure of leaflets.