Abscisic Acid Synthesis and Metabolism in Wheat Ears

During development of wheat grains their content of abscisic acid (ABA) increased, and this was also shown to occur in the grain of ears detached and grown in culture. Over a 10-day period of growth of ears in culture, their content of ABA increased from 0.31 to 2.56 ng/grain. Loss of ABA from the grain occurred on cessation of grain growth and drying of the grain. With loss of ABA, there was an associated but lesser accumulation of phaseic acid and dihydrophaseic acid, two known metabolites of ABA. Studies with [14C]abscisic acid indicated that premature drying of grain led to some conversion of ABA to compounds chromatographically similar to phaseic and dihydrophaseic acid, but the major products were more polar. Apparently, synthesis of ABA occurred in the developing grain (or at least in the ear) in association with a slow rate of degradation but, at maturity and drying of the grain, there was enhanced degradation of ABA. The physiological importance of these compounds in grain development and dormancy is discussed.