Loss of kernel set due to water deficit and shade in maize: Carbohydrate supplies, abscisic acid, and cytokinins

To advance our understanding of the underlying processes by which kernel set is regulated in maize (Zea mays L.), leaf photosynthesis, sugars, starch, abscisic acid (ABA), and cytokinin were quantified in plants subjected to water deficit and shade, imposed for 5 d at the pre-pollination and early post-pollination stages. Both water and light deprivation, at both stages, decreased kernel set primarily in apical ear regions. Treatments decreased leaf photosynthesis similarly; however, sugar concentrations in reproductive tissues increased in water deficit while they decreased 20 to 50% in shade. During treatments, nonstructural carbohydrate accumulation was nearly halted in both apical and basal florets at the pre-pollination stage, whereas it was decreased to a greater extent in apical than basal endosperm/nucellus at the post-pollination stage. Both water deficit and shade increased ABA concentrations in reproductive tissues, but only at the post-pollination stage was ABA greater in apical than basal ear zones, thus corresponding to effects on kernel set. Treatments did not consistently after zeatin-like cytokinin concentrations. We conclude that photosynthate flux and ABA are components of a regulatory system by which water and light deprivation affect kernel set at the post-pollination stage, while additional factors may underlie effects at the pre-pollination stage.