Relationship of Carbohydrate and Abscisic Acid Levels to Kernel Set in Maize under Postpollination Water Deficit

Maize (Zea mays L.) yield is substantially diminished by drought during the initial phase of kernel development. To advance our understanding of the mechanisms underlying this response, we determined the timing of sucrose, glucose, starch, and abscisic acid (ABA) accumulation in apical (inferior) and basal (superior) kernels during water deficit (3-8 d after pollination) and recovery. While net flux of material was nearly zero into both apical and basal kernels during stress, growth resumed after rewatering only in basal kernels. In bulk tissues of pedicel-placenta, pericarp, or endosperm, basal kernels did not have higher glucose, sucrose, or starch concentrations than apical kernels. However, glucose and sucrose concentration in the pedicel endosperm interface where phloem terminates was maintained at control concentrations in basal kernels, while it was depleted in apical kernels. Kernel set in basal versus apical kernels was also associated with lower levels of ABA in the pedicel-placenta tissue of basal kernels after rewatering. These findings support a model of interacting influences of carbohydrate and ABA, and suggest that this interaction might be a good target for future efforts to genetically improve maize drought tolerance.