[Changes of endogenous hormone contents and antioxidative enzyme activities in wheat leaves under low temperature stress at jointing stage].

Low temperature stresses (-3 and -5 °C) were simulated using artificial temperature-controlled phytotrons to study the freezing rate, the contents of endogenous hormones, and the activities of antioxidative enzymes in the leaves of wheat plants of Yangmai 16 (YM 16) and Xumai 30 (XM 30) at jointing stage. The grade and index of freezing injury increased with lower temperature and longer stress. The freezing rate was at the 5th level and the main stems and tillers of both cultivars were finally dead under -5 °C lasting for 72 h. On the last day of stress initiation, the contents of abscisic acid (ABA) and zeatin riboside (ZR), and the activities of superoxide dismutase (SOD), peroxide dismutase (POD), and catalase (CAT) in leaves increased at the beginning and then declined as low temperature progressed. On the 3rd day after stress, the contents of ABA and ZR and the activities of antioxidative enzymes were higher than those on the last day of cold stress, and then reduced to the level of the control on the 6th day after stress. The content of gibberellins (GA3) was lowered by cold stress. For YM 16, GA3 content increased from the 3rd day to the 6th day after cold stress, whereas, for XM 30, it increased first and then decreased. For the treatment of -5 °C lasting for 72 h, the contents of hormones and the activities of antioxidative enzymes were significantly lower than those of the other treatments. Correlation analyses showed that higher ABA and ZR contents, and higher SOD, POD and CAT activities as well as lower GA3 content could alleviate the low-temperature injury in wheat plants under low temperature stress.