Abstract: Drought is one of the most important abiotic stresses limiting wheat yield. To clarify the responses of different winter wheat varieties to post-anthesis drought, we investigated changes of flag leaf photosynthetic characteristics, malondialdehyde content, activities of antioxidant enzymes, content of osmotic adjustment substances, and activities of C4 photosynthetic enzymes in various organs of two winter wheat cultivars, “Jingdong 18” (drought-sensitive) and “Nongda 211” (drought-resistant), under drought and rewatering treatments. The results showed that post-anthesis drought significantly reduced the 1000-grain weight of “Jingdong 18”, but did not affect that of “Nongda 211”. Compared with “Jingdong 18”, SPAD value and net photosynthetic rate in flag leaves of “Nongda 211” were higher, the F_v/F_m  value was more stable, the increment of malondialdehyde content was smaller, and the increment of SOD and POD activities and soluble protein and proline content was greater. The activities of C4 photosynthetic enzymes (PEPC, NADP-ME and PPDK) in spikes (glumes and grains) were higher than those in flag leaves, which were enhanced under drought stress. After rewatering, various indices were restored to some extent. The results of correlation analysis showed that the increment of C4 photosynthetic enzyme activities in spikes was significantly positively correlated to the increment of proline content and antioxidant enzyme activity in flag leaves under post-anthesis drought. In conclusion, post-anthesis drought reduced photosynthetic capacity of wheat flag leaves, accelerated membrane lipid peroxidation and chlorophyll degradation, and finally affected wheat yield. Cultivars with strong drought-resistance maintained grain weight and slowed yield decline by enhancing C4 photosynthetic enzyme activities in spikes, osmotic regulation and antioxidant capacity in flag leaves under drought stress.

Key words: post-anthesis drought, C4 photosynthetic enzyme, winter wheat, antioxidant enzyme.