Role of NO Synthesis Modification in the Protective Effect of Putrescine in Wheat Seedlings Subjected to Heat Stress

The role of nitric oxide and its functional relations to reactive oxygen species (ROS) and calcium are studied in relation to the stress-protective effects of the polyamine putrescine in wheat seedlings (Triticum aestivum L.) subjected to heat stress. The treatment of seedlings with 1 mM putrescine causes a rapid, transient rise in the NO content in roots in the first 24 h, which peaks 1 h after the beginning of exposure. It was noted a doubling of the activity of diamine oxidase (DAO) and the reduction of nitrate reductase activity in roots by 25–30%. The DAO inhibitor aminoguanidine completely eliminated the putrescine-induced increase in the NO content. The increase in the DAO activity and NO content was also eliminated by the treatment of seedlings with the calcium antagonists ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) and neomycin. The scavenger of nitric oxide 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) completely counteracted the effect of hydrogen peroxide increase in weat seedlings roots treated by putrescine. In the meantime, treatment with dimethylthiourea, a hydrogen peroxide antagonist, only slightly reduced the putrescine-induced rise in NO content in the roots. The NO, ROS, and calcium antagonists eliminated the protective effect of putrescine during heat stress, which was determined by the intensity of lipid peroxidation and seedling survival. We draw a conclusion concerning the role of nitric oxide synthesized via the oxidative pathway and its functional relations to ROS and calcium ions in the stress-protective effect of putrescine in plant objects.