Induction of Sensitivity to Gibberellic Acid in Wheat and Barley Caryopses: Effects of Dehydration, Temperature and the Role of the Embryo during Caryopsis Maturation

The development of gibberellic acid sensitivity, which is measured by the level of α-amylase activity, has been investigated by comparing enzyme levels in freshly detached wheat and barley caryopses cultured on moist filter paper for various times and temperatures with those in caryopses dried over 35% (w / w) glycerol-water solutions or in caryopses air-dried in detached ears at controlled temperatures and by comparing enzyme levels in de-embryonated caryopses with intact ones, both being cultured in aqueous buffer solutions. Similar amounts of enzyme were produced in caryopses held moist or dried, although the duration of the lag period, and the rate of accumulation of α-amylase were markedly influenced by the length and temperature of main treatments. Likewise similar amounts of enzyme were produced in de-embryonated and intact caryopses cultured in an aqueous buffer if the latter were de- embryonated prior to incubation in solutions of gibberellic acid. However, when intact or de-brushed (removal of the apical tip) caryopses were incubated with GA3, less α-amylase was found in these incubates than in those incubates containing de-embryonated caryopses. These observations were found in incubates of both sensitized freshly harvested and normal mature caryopses. It is concluded that drying is not essential for the development of gibberellic acid sensitivity in the wheat and barley caryopses.