Regulation of Maize Kernel Carbohydrate Metabolism by Abscisic Acid Applied at the Grain-Filling Stage at Low Soil Water Potential

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.