Effect of temperature on antioxidation mechanism of wheat (Triticum aestivum L.) seedlings under salt stress

The objective of this study was to elucidate the role of temperature in antioxidation mechanism of eight wheat cultivars differing in salt tolerance. The eight cultivars seedlings were cultured in nutrient solutions at normal (20 ℃ / 25 ℃) and low (10 ℃ / 15 ℃) temperature conditions. The wheat cultivars were set under 150 mmol·L^-1 NaCl stress condition for 48 h at the third leaf stage of the seedlings. Then reactive oxygen species (ROS) accumulation, antioxidant enzyme activity and electrolyte leakage (EK) were examined in the eight wheat cultivar seedlings. The results showed that the activities of SOD, POD, CAT and APX in salt-tolerant cultivars increased significantly, and were higher than those of salt sensitive cultivars under salt stress with normal temperature condition. As for salt sensitive cultivars, salt stress only enhanced APX activity. Accumulated ROS and EK in salt sensitive cultivar seedlings were higher than those in salt-tolerant cultivar seedlings. For drought-tolerant cultivars, the values of above parameters were between those of salt-tolerant and salt-sensitive cultivars. Under low temperature, GR activity of all the experimental cultivars increased by 2?3 folds under salt stress compared with that of non-salt-stress treatments. While CAT and APX activities in salt-tolerant cultivars increased significantly, SOD, POD and APX activities in drought-tolerant cultivars obviously improved under salinity stress conditions. Also in salt-sensitive cultivars, SOD and POD activities enhanced markedly under salinity stress conditions. The response of antioxidative enzymes to salt stress under low temperature was different from that under normal temperature. Under low temperature, SOD and POD activities were inhibited in salt-tolerant cultivars seedlings. The excessive ROS induction was stopped mainly by enhanced activities of APX and GR, two key enzymes of ascorbic acid-GSH cycle. For drought-tolerant and salt-sensitive cultivars, salinity stress obviously increased SOD, POD and GR activities, as well as GR activity. As a result of the interaction of antioxidative en-zymes, different scopes of ROS accumulation and EK in wheat cultivars with different levels of salt tolerance reduced under low temperature conditions compared with normal temperature condition.