Prolonged Exposure of Grapevine Buds to Low Temperatures Increases Dormancy, Cold Hardiness, and the Expression of Vvα-AMYs Genes

Abstract

Grapevine buds, like the buds of most temperate fruit trees, require a certain amount of chilling during the winter in order to emerge homogeneously in spring. This phenomenon is referred to as the chilling requirement (CR). The underlying mechanism of CR is unknown. As previously reported, low temperatures have a dual effect on grapevine buds, favoring release of buds from endodormancy (ED) while at the same time increasing cold hardiness (CH). To analyze whether CR is related to one or both of these processes, the BR50 (time required to reach 50 % bud break under forced conditions) and the low-temperature exotherm (LTE), which measures depth of ED and level of CH, respectively, were determined over the annual cycle of grapevine, and the results demonstrated that ED and CH occur sequentially. Using single-bud cuttings, the effect of low temperatures on both starch content and the expression of Vvα-AMYs were studied, and low temperatures resulted in increased ED and CH and stimulated starch breakdown through the activation of Vvα-AMYs, similar to that described in storage organs of higher plants such as tubers and bulbs. It has also been reported that abscisic acid (ABA) increases ED and CH in grapevine buds. Here, we confirmed that ABA synergizes the effect of low temperatures on CH and that low temperatures resulted in the up-regulation of VvNCED1, a gene encoding for a key enzyme of ABA biosynthesis. These results suggest that low temperature-induced increases in ED and CH could be mediated by ABA.