Abstract: A field plot experiment was conducted to study the effects of foliar spraying DA-6 at the rates of 10, 20, and 40 mg·L^-1at jointing stage on the leaf photosynthetic carboxylase and protective enzyme activities and grain yield of high-yielding summer maize cultivar Denghai 661. Comparing with the control (foliar spraying surfactant and water), spraying 10, 20, and 40 mg·L^-1 of DA-6 increased the grain yield of Denghai 661 significantly, with the increment being 10.0%, 8.9%, and 9.4%, respectively, but no significant differences were observed among the DA-6 treatments. Different concentration DA-6 increased the leaf area index, net photosynthetic rate, and RuBPCase and PEPCase activities significantly, and the promotion effects on the net photosynthetic rate and RuBPCase and PEPCase activities increased with increasing concentration of DA-6. After treated with DA-6, the leaf superoxide dismutase, catalase, peroxidase, and gultathione S-transferase activities and the leaf soluble protein content at the stages of silking, grain-filling, milky, and wax maturity all increased significantly, and the leaf malondialdehyde decreased significantly, compared with the control. The catalase activity increased with increasing DA-6 concentration, but the other indices had no significant differences among the DA-6 treatments.

Key words: high-yielding summer maize, DA-6, yield, photosynthetic carboxylase, protective enzyme, Cyclobalanopsis gilva, leaf, anatomical characteristics, drought stress.