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Articles

Water Stress Enhances Expression of an -Amylase Gene in Barley Leaves

Commonwealth Scientific and Industrial Research Organization, Division of Plant Industry, Canberra, A.C.T. 2601, Australia

The amylases of the second leaves of barley seedlings (Hordeum vulgare L. cv Betzes) were resolved into eight isozymes by isoelectric focusing, seven of which were -amylase and the other, -amylase. The -amylase had the same isoelectric point as one of the gibberellin-induced -amylase isozymes in the aleurone layer. This and other enzyme characteristics indicated that the leaf isozyme corresponded to the type A aleurone -amylase (low pI group). Crossing experiments indicated that leaf and type A aleurone isozymes resulted from expression of the same genes.

In unwatered seedlings, leaf -amylase increased as leaf water potential decreased and ABA increased. Water stress had no effect on -amylase. -Amylase occurred uniformly along the length of the leaf but -amylase was concentrated in the basal half of the leaf. Cell fractionation studies indicated that none of the leaf -amylase occurred inside chloroplasts.

Leaf radiolabeling experiments followed by extraction of -amylase by affinity chromatography and immunoprecipitation showed that increase of -amylase activity involved synthesis of the enzyme. However, water stress caused no major change in total protein synthesis. Hybridization of a radiolabeled -amylase-related cDNA clone to size fractionated RNA showed that water-stressed leaves contained much more -amylase mRNA than unstressed plants. The results of these and other studies indicate that regulation of gene expression may be a component in water-stress induced metabolic changes.

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