When drought occurs during the maize-filling period, the probability of yield decline increases. Abscisic acid (ABA) plays a regulatory role in physiological and metabolic activities during plant development. However, its effect on the antioxidant system of maize leaves during the grain-filling stage is unclear. Maize plants (Zhengdan958) were used as an experimental material, and ABA was sprayed on the leaves during the grain-filling stage. The plants were placed under drought conditions to analyze the relationship between the ascorbate-glutathione (AsA-GSH) cycle and hydrogen peroxide (H2O2) removal. Exogenous ABA significantly reduced the malondialdehyde content, relative electrolyte leakage, and H2O2 under drought stress. This is similar to the exogenous ABA effect on the AsA-GSH cycle. Exogenous ABA upregulated the transcription of related genes and alleviated the inhibition of drought stress on the monodehydroascorbate reductase and dehydroascorbate reductase activities, thereby further increasing the ascorbate peroxidase and glutathione reductase activities. It contributed to an increase in the AsA and GSH levels and inhibited the decrease in the AsA/dehydroascorbic acid and GSH/oxidized glutathione ratios. Therefore, exogenous ABA plays an important role in improving the antioxidant capacity and drought resistance physiology of maize by enhancing antioxidant enzyme activity and stabilizing the AsA and GSH redox state.

A water deficit during the grain-filling stage increases the frequency of yield loss in maize (Zea mays L.). Abscisic acid (ABA) plays a regulatory role in many stages of plant growth; however, its effects on sucrose-metabolizing enzyme activities under stress are poorly understood. The activities of cell-wall-bound acid invertase, vacuolar invertase, cytoplasmic invertase, and sucrose synthase decreased continuously under drought stress, whereas ABA treatment partially restored these activities. In addition, the increase and development of sucrose content under drought stress were related to invertase activity. Up-regulation of the activities and gene expression of cell-wall-bound acid invertase and vacuolar invertase with ABA treatment contributed to the increase in the number of rows and number of grains per row. Furthermore, ABA inhibited the increase in the length of the bald tip. Compared with the control group, water stress significantly reduced the yield index, with the lowest yield index on the 10th day of stress. These results suggest that the increase in ABA-induced sucrose-metabolizing enzyme activity might be an effective mechanism to improve maize drought resistance at the grain-filling stage.