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Water stress enhances expression of an alpha-amylase gene in barley leaves |
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| Authors: | Jacobsen J V Hanson A D Chandler P C |
| Affiliation: | Commonwealth Scientific and Industrial Research Organization, Division of Plant Industry, Canberra, A.C.T. 2601, Australia. |
| Abstract: | 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 β-amylase and the other, α-amylase. The α-amylase had the same isoelectric point as one of the gibberellin-induced α-amylase isozymes in the aleurone layer. This and other enzyme characteristics indicated that the leaf isozyme corresponded to the type A aleurone α-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 α-amylase increased as leaf water potential decreased and ABA increased. Water stress had no effect on β-amylase. α-Amylase occurred uniformly along the length of the leaf but β-amylase was concentrated in the basal half of the leaf. Cell fractionation studies indicated that none of the leaf α-amylase occurred inside chloroplasts. Leaf radiolabeling experiments followed by extraction of α-amylase by affinity chromatography and immunoprecipitation showed that increase of α-amylase activity involved synthesis of the enzyme. However, water stress caused no major change in total protein synthesis. Hybridization of a radiolabeled α-amylase-related cDNA clone to size fractionated RNA showed that water-stressed leaves contained much more α-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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