Hormonal regulation of early kernel development

To attain maximum yield across environments, grain crops adjust the development of sink capacity to balance changes in the supply of assimilates. In maize (Zea mays L.) and other cereal crops, much of this adjustment is achieved by regulating the extent of kernel abortion. In nonstressed, optimal environments, hormones play important roles in coordinating the timing of development among kernel constituent tissues, and in regulating the overall rate of kernel growth. During the early phases of development when endosperm cell division predominates, environmental stresses induce a high rate of kernel abortion. High temperature stress decreases cytokinin levels; water deficit increases abscisic acid levels; and other stresses increase ethylene levels. Stress-induced changes in rates of hormone synthesis, flux, and/or turnover appear to regulate the abortion process. In well-adapted genotypes these processes are tightly regulated so excess loss of sink capacity does not occur. Much remains to be learned about the roles of hormones in regulating kernel set during post-pollination kernel development. Advances in cellular and molecular techniques, and their recent application to the study of hormone metabolism and signaling, offer a significant opportunity to advance our understanding of the role of hormones in regulation of early kernel development.