Distribution of Abscisic Acid in Maize Kernel during Grain Filling

The distribution of abscisic acid (ABA) within maize (Zea mays L.) kernels was studied in kernels from nontreated plants, from plants in which assimilate supply had been altered by source/sink manipulations, and in kernels cultured in vitro on ABA-free media. Prior to growth of the embryo, both the pedicel/placento-chalazal complex and the endosperm contained high concentration of ABA; however, the quantity of ABA in these tissues declined as the concentration in the embryo increased during the early stages of embryo growth. Peaks in the levels of ABA appeared to occur prior to and not concurrent with physiological events during grain filling. During most of the grain filling period, ABA concentration in the embryo was higher than that found in other kernel components. Altering assimilate supply by partial defoliation at two stages of development resulted in variable and transient effects on the relative distribution and concentration of ABA in kernel components. The concentration and distribution of ABA among components of kernels grown in vitro was similar to that observed for field-grown kernels. On the basis of these findings, in situ synthesis of ABA by kernel components is implicated and the putative role of ABA in the regulation of kernel development is discussed.