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

Abstract

It has been suggested that respiratory stress is involved in the mechanism underlying the dormancybreaking 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 -amylase genes (Vv˛-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˛-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˛-AMY gene expression during the hypoxia treatment was found, suggesting that soluble sugars mediate the effect of hypoxia on Vv˛-AMY gene expression. Exogenous applications of soluble sugars and sugar analogs confirmed this finding and revealed that osmotic stress induces the expression of Vv˛-AMY1 and Vv˛-AMY3 and that soluble sugars induces Vv˛- AMY2 and Vv˛-AMY4 gene expression. Interestingly, the plant hormone gibberellic acid (GA3) induced the expression of Vv˛-AMY3 and Vv˛-AMY4 genes, while dormancy breaking stimuli, chilling and cyanamide exposure, mainly induced the expression of Vv˛-AMY1 and Vv˛-AMY2 genes, suggesting that these two -amylase genes might be involved in the release of grapevine buds from the ED.