Relationship Between Endodormancy and Cold Hardiness in Grapevine Buds

Abstract

Endodormancy (ED) and cold hardiness (CH) are two strategies utilized by grapevine (Vitis vinifera L.) buds to survive unfavorable winter conditions. Each phenomenon is triggered by different environmental cues—ED by short-day (SD) photoperiod and cold hardiness (CH) by low temperatures. In grapevine buds, CH occurs mainly via the supercooling of intracellular water, a phenomenon associated with the low temperature exotherm (LTE). The seasonal dynamics of ED and CH were studied on grapevines buds by determining the BR50 (time required to reach 50 % of bud break under forced conditions) and the LTE, which measure the depth of ED and the level of CH, respectively. Overlapping BR50 and LTE curves revealed that CH began to develop in late April, when buds were fully endodormant and daily mean temperatures had started to drop below 14 C, suggesting that ED is a prerequisite for the acquisition of full CH. Increase in starch content and thickening of the cell wall (CW) of meristematic cells which occurs in dormant buds could be involved in structural and metabolic changes that favor CH subsequent acquisition. Interestingly, the thickening of the CW and the synthesis of starch which are associated with ED were induced by a SD-photoperiod, while the hydrolysis of starch, the accumulation of soluble sugars, and the upregulation of dehydrin genes, which are associated with CH, were induced by low temperatures. Overall, the results indicate that structural, metabolic, and transcriptional changes that occur during ED in grapevine buds are necessary for the further development of CH.