The dormancy-breaking stimuli chilling, hypoxia and cyanamide exposure up-regulate the expression of α-amylase genes in grapevine buds

It has been suggested that respiratory stress is involved in the mechanism underlying the dormancy-breaking effect of hydrogen cyanamide (H2CN2) and sodium azide in grapevine buds; indeed, reductions in oxygen levels (hypoxia) and inhibitors of respiration promote bud-break in grapevines. In this study, we showed that, hypoxia increased starch hydrolysis soluble sugar consumption and up-regulated the expression of alpha-amylase genes (Vv alpha-AMYs) in grapevine buds, suggesting that these biochemical changes induced by hypoxia, may play a relevant role in the release of buds from endodormancy (ED). Three of the four Vv alpha-AMY genes that are expressed in grapevine buds were up-regulated by hypoxia and a correlation between changes in sugar content and level of Vv alpha-AMY gene expression during the hypoxia treatment was found, suggesting that soluble sugars mediate the effect of hypoxia on Vv alpha-AMY gene expression. Exogenous applications of soluble sugars and sugar analogs confirmed this finding and revealed that osmotic stress induces the expression of Vv alpha-AMY1 and Vv alpha-AMY3 and that soluble sugars induces Vv alpha-AMY2 and Vv alpha-AMY4 gene expression. Interestingly, the plant hormone gibberellic acid (GA(3)) induced the expression of Vv alpha-AMY3 and Vv alpha-AMY4 genes, while dormancy breaking stimuli, chilling and cyanamide exposure, mainly induced the expression of Vv alpha-AMY1 and Vv alpha-AMY2 genes, suggesting that these two alpha-amylase genes might be involved in the release of grapevine buds from the ED. (C) 2013 Elsevier GmbH. All rights reserved.