Development of Responsiveness to Gibberellic Acid in the Aleurone Layer of Immature Wheat and Barley Caryopses: Effect of Temperature

Abstract

Immature wheat caryopses were dried at different temperatures ranging from 4 to 30°C and the kinetics of increase of α-amylase activities in endosperm halves treated with gibberellic acid were investigated. Over the duration of the experiments the kinetic curve comprised of lag, curvilinear and linear phases, and the curvilinear phase could be fitted by a quadratic expression. The square root of α-amylase activity due to gibberellic acid was linearly related to time and from this the acceleration rate of production of α-amylase and duration of lag phase could be calculated. The calculated acceleration rate for the production of α-amylase was correlated with drying temperatures below 20°C but not above. The lag phase for dry endosperm halves was biphasic, consisting of a gibberellic acid insensitive phase (hydration phase) and a hormone sensitive phase, the only phase present in fully imbibed endosperm halves. Duration of the hydration phase was inversely correlated with drying temperatures below 15°C but not above, whereas the duration of the subsequent hormone sensitive phase was not correlated with drying temperature. It was concluded that low drying temperatures modified the subsequent behaviour of the aleurone layer, delaying the onset and reducing the rate of gibberellic acid-induced processes, which culminate in the production of °-amylase.