PHYSIOLOGICAL, HORMONAL AND MOLECULAR TRAITS ARE AFFECTED BY WATER STRESS IN VITIS

Wild grapevine (Vitis vinifera L.) was domesticated by humans several millennia ago, probably in the Asia Minor region. Nowadays, grapevine is a crop cultivated worldwide for the production of wine, fresh and withered grapes, fruit juices and spirits. From a different perspective, grapevine results as one of the most important fruit crops due to its high income value; moreover, grapevine is profoundly tied to cultural and religious traditions. Grapevine is traditionally cultivated in areas characterized by Mediterranean climate, thus duelling with high temperature and rain scarcity in summer season. In fact, grapevine is considered a quite tolerant crop to drought conditions. Nonetheless, negative effects of drought affect yield and grape quality of vineyards, and this situation is being exasperated by climate change occurrence. For those reasons, grapevine draws notable interest of agricultural research in particular for physiological studies in plant water relations. In this picture, this PhD thesis is inserted, examining modifications ranging from plant physiology to berry quality. In different experiments carried out on different grapevine varieties, acclimation processes to water stress were revealed and discussed. In particular, the involvement of non-structural carbohydrates (NSC) appeared fundamental in the acclimation to drought for both the different allocation to plant organs and for their contribution to osmotic adjustments. Together with changes in NSC, our data highlighted contextual modifications in newly formed organs, and particularly xylem vessels narrowing was observed in grapevine petioles. A special focus on drought tolerance in grapevine suggests shifted hormonal profiles, in cultivars exhibiting a different degree of tolerance to water stress. Surprisingly, abscisic acid did not show a different modulation between the more tolerant and the more susceptible considered varieties. The same two varieties showed also different expression patterns of several aquaporins (AQPs) genes in both irrigated and not conditions. Thus, AQPs was confirmed as potential targets capable to modulate drought tolerance in grapevine. Finally, looking at the most important destination of grapevine fruits, we moved our attention to water stress effects on the flavonoid grape composition. Regarding this, flavonoids is one of the most important class of secondary metabolisms that have a great impact on red wine properties. Nonetheless, the impact of water stress on these secondary metabolites is still contradictory. Firstly, the effect of two water deficient regimes on the anthocyanins and proanthocyanidins content in Refošk grapes was studied. Our data highlighted positive effects of the more limiting water regime on berry quality in terms of concentrations of both anthocyanins and proanthocyanidins. Successively, we explored the effects of water stress directly on the genes of the flavonoid pathway, and a putative gene responsible for proanthocyanidins galloylation was investigated. The results of this second work were in agreement with the previous and added some light on the flavonoid modifications. The outcomes of the experiments carried out in the thesis, contribute to better understand the impact of water stress on grapevine physiology. Although some results were clear and allowed a strong discussion, there are still some obscure trends that will require more in deep further investigations in future.