Effect of High Temperature on Photosynthetic Capability and Antioxidant Enzyme Activity of Flag Leaf and Non-leaf Organs in Wheat

Winter wheat in North China has been subject to high temperature stress during grain filling. The purpose of this study was to determine the effect of high temperature on the photosynthetic capability of flag leaf and the antioxidant system of flag leaf and non-leaf organs in winter wheat cultivars Shijiazhuang 8(tolerant to high temperature) and Henong 341(sensitive to high temperature). High temperature(HT) stress was imposed with a plastic shed from the 8th to the 22 nd day after anthesis, and normal temperature was used as the control. Under HT, the photosynthetic rate and chlorophyll content of flag leaf decreased by 18.7%–24.9% and 5.7%–6.2%, respectively; whereas the malodialdehyde(MDA) and proline(Pro) contents in flag leaf blade, sheath, peduncle, glume and grain increased in different levels. The increased percentage of MDA was higher in flag leaf than in non-leaf organs and that of Pro was higher in non-leaf organs than in flag leaf. Superoxide dismutase(SOD) in flag leaf, glume and grain, catalase(CAT) in flag leaf, sheath and grain, and peroxidases(POD) in flag leaf, sheath and glume were induced at early stage(4 d after treatment) by HT treatment, while the activities of antioxidant enzymes in other organs increased at later stage(7 d after treatment). Thereafter, the activities of antioxidant enzymes in various organs maintained lower levels compared with those of the control. At the 26 th day after anthesis when HT stress was relieved for four days, the SOD activity in sheath, peduncle and glume and the POD activity in flag leaf, glume and grain began to increase, but the effects of HT on the SOD and POD activities in other organs and the CAT activity in all organs seemed irreversible. In general, the non-leaf organs exhibited higher antioxidant capability and heat tolerance than flag leaf. Compared with Henong 341, Shijiazhuang 8 exhibited higher cell membrane stability and antioxidant activity in leaf and non-leaf organs, leading to a tolerance to HT stress of the whole plant. This might be the physiological basis of smaller percentage of yield loss in Shijiazhuang 8 than in Henong 341 under HT stress. Our results indicate that non-leaf organs of wheat play an important role in adaptability to climate warming.