Regulation of alpha-galactosidase gene expression in primary foliage leaves of barley ( Hordeum vulgare L) during dark-induced senescence.

alpha-Galactosidase activity (alpha- d-galactoside galactohydrolase, EC 3.2.1.22) increased during dark-induced senescence in primary foliage leaves of barley ( Hordeum vulgare L. cv. Steffi). The changes in activity were accompanied by parallel changes in expression of the HvSF11 gene encoding a putative alpha-galactosidase. The transcript level of HvSF23 encoding a second putative alpha-galactosidase stayed constant during leaf senescence. Both alpha-galactosidase activity and the level of the HvSF11 transcript decreased after exogenous application of sucrose and glucose to detached dark-incubated leaves. In contrast, the HvSF23 transcript level was not influenced by sugars. Application of glucose analogs to detached and dark-incubated leaves revealed that phosphorylation of hexose by hexokinase modulates both the alpha-galactosidase activity and the expression of HvSF11. These results indicate that the expression of the genes coding for two alpha-galactosidase isoenzymes is regulated by different signalling pathways, suggesting different functions for the two gene products.