Mechanisms Of Nitric Oxide Confering Salt Tolerance To Wheat (Triticum Aestivum L.) Seedlings Against Salt Stress

It could be summerized from the changes of chlorophyll contents, MDA contents and plasma membrane permeability that 0.1 and 1 mmol/L sodium nitroprusside (SNP), a donor of nitric oxide (NO), markedly alleviated the oxidative damage to wheat (Triticum aestivum L.) seedling leaves caused by 150 and 300 mmol/L NaCl salt stress respectively. Compared with those of wheat seedlings under salt stress, 0.1 and 1 mmol/L SNP treatment significantly enhanced the activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), which contributed to the delay of 02" and HiO2 accumulation in respond to exogenous NO donor in wheat seedling leaves under 150 and 300 mmol/L NaCl salt stress respectively. But it displayed no any effects on the activities of guaiacol peroxidase (POD). Besides the reactive oxygen species (ROS) eliminating enzymes, GSH has also been confirmed involving in the regulation of exogenous NO donor on the metabolism of ROS. Results showed that 150 and 300 mmol/L NaCl salt stress both caused the decrease of reduced glutathione (GSH) in wheat leaves in various degrees, and as a consequence, the contents of oxidized glutathione (GSSG) increased. However, 0.1 and 1 mmol/L SNP treatment dramatically increased GSH content but demonstrated no functions on the content of GSSG. Importantly, through analyzing the ratio of GSHrGSSG showed that exogenous NO donor elevated the ratio of GSH:GSSG in wheat seedling leaves when subjected to salt stress, which might be due to the increased activities of glutathione reductase (GR) exerted by exogenous NO donor. Meanwhile, exogenous NO donor also promoted the activities of GSH-dependent glutathione-S-transferase (GST) in wheat seedling leaves under salt stress, participating the degradation of peroxides caused by saltstress and achieving its cell detoxification function.In order to confirm the specific role of NO and elucidate its mechanisms of salt tolerance. We mainly took 150 mmol/L NaCl stress as example and investigated the changes of fresh weight, growth rate and relative water content of wheat seedlings in respond to exogenous NO donor under salt stress. The results uncovered that 0.1 mmol/L SNP treatment significantly alleviated the growth inhibition, counteracted the the fresh weight and the growth rate loss, and delayed the decay of chlorophyll caused by 150 mmol/L NaCl salt stress. While, 1 mg/ml hemoglobin (specific NO scavenger) treatment completely reverted above SNP actions by restoring the growth of wheat seedlings and the chlorophyll contents to the levels found in non-SNP treated wheat seedlings under salt stress conditions. Considering that NO2" and [Fe(CN)6]3" were the byproducts when SNP smelting to water, whereas, using NaNO2 and K3[Fe(CN)6] as control further confirmed the specific role of NO confering the salt tolerance to wheat seedlings. Further investigations showed that the NO induced salt tolerance of wheat seedlings might be owe to the inducement of plasma membrane FT'-ATPase and PPase activities by NO, supplying necessary energy for the growth of wheat seedlings under stress conditions. Employment of exogenous CaSO4 and EGTA, the chelator of Ca2+, confirmed the involvement of Ca2+ as a vital factor to the NO induced activities of plasma membrane H^ATPase and PPase in wheat seedling roots under salt stress. Further investigation of Na+ and K+ in roots in respond to NO under salt stress uncovered that exogenous NO did not obviously affect the content of Na+, but significantly elevated the content of K+ as well as leading to the increase of K+ to Na+ ratio in wheat seedling roots under salinity conditions. And the enhanced K+ by NO might contribute to the activation of plasma membrane H+-ATPase activities. The ratio of K+/Na+ could act as the signalling inducing the adaptive abilities of wheat seedlings against NaCl salt stress, and which might be also an important reason to the NO induced salt tolerance.It is well known that, plants induce various biochemical and physiological responses to survive the adverse environmental...