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Plant and Cell Physiology, 1996, Vol. 37, No. 8 1116-1125
© 1996

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

Liwen Jiang1,3, Allison R. Kermode1 and Russell L. Jones2

1Department of Biological Sciences, Simon Fraser University Burnaby, British Columbia, Canada, V5A 1S6
2Department of Plant Biology, 111 Koshland Hall, University of California Berkeley, CA 94720-3102, U.S.A.

The effect of premature drying on the sensitivity of aleurone layer cells of developing barley (Hordeum vulgare L.) grain to gibberellic acid (GA3) was investigated. The capacity of barley aleurone layer cells to respond to GA3, as indicated by {alpha}-amylase synthesis and secretion by de-embryonated grain, increased during the later stages of development. Aleurone layers of immature grain (younger than 30 d after anthesis; DAA) were not capable of producing {alpha}amylase in response to GA3; however, premature drying at this stage promoted GA-responsiveness resulting in the induction of mRNA for {alpha}-amylase and increased {alpha}-amylase synthesis and secretion. Preincubation of the immature grain or its maintenance at 100% relative humidity prior to exposure of the de-embryonated grain to GA3 also led to an enhanced capacity of the aleurone layer to produce {alpha}amylase and its mRNA as compared to the fresh, untreated grain. However, the amount of mRNA and enzyme produced was much lower than that induced by premature drying. Moreover, following these nondrying treatments, the aleurone layer cells remained unresponsive to exogenous GA3; the same amount of enzyme was produced in the absence of applied GA3. Transient expression of chimeric gene constructs in aleurone layer cells of de-embryonated grain suggest that drying up-regulates the {alpha}-amylase gene promoter in response to GA3. We conclude that desiccation is required for barley aleurone layer cells to become responsive to GA3 and hence express their full potential for {alpha}amylase synthesis and secretion.

3Present address: Department of Biochemistry, University of Missouri, 117 Schweitzer Hall, Columbia MO 65211, U.S.A.

(Received May 20, 1996; Accepted September 10, 1996)
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