Premature Drying Increases the GA-Responsiveness of Developing Aleurone Layers of Barley (Hordeum vulgare L.) Grain

The effect of premature drying on the sensitivity of aleuronelayer cells of developing barley (Hordeum vulgare L.) grainto gibberellic acid (GA₃) was investigated. The capacity ofbarley aleurone layer cells to respond to GA₃, as indicatedby -amylase synthesis and secretion by de-embryonated grain,increased during the later stages of development. Aleurone layersof immature grain (younger than 30 d after anthesis; DAA) werenot capable of producing amylase in response to GA₃; however,premature drying at this stage promoted GA-responsiveness resultingin the induction of mRNA for -amylase and increased -amylasesynthesis and secretion. Preincubation of the immature grainor its maintenance at 100% relative humidity prior to exposureof the de-embryonated grain to GA₃ also led to an enhanced capacityof the aleurone layer to produce amylase and its mRNA as comparedto the fresh, untreated grain. However, the amount of mRNA andenzyme produced was much lower than that induced by prematuredrying. Moreover, following these nondrying treatments, thealeurone layer cells remained unresponsive to exogenous GA₃;the same amount of enzyme was produced in the absence of appliedGA₃. Transient expression of chimeric gene constructs in aleuronelayer cells of de-embryonated grain suggest that drying up-regulatesthe -amylase gene promoter in response to GA₃. We conclude thatdesiccation is required for barley aleurone layer cells to becomeresponsive to GA₃ and hence express their full potential foramylase synthesis and secretion. ³Present address: Department of Biochemistry, University ofMissouri, 117 Schweitzer Hall, Columbia MO 65211, U.S.A.