Vitis vinifera and drought stress: physiological and anatomical responses

Climate change represents a threat to natural ecosystems as well as to agricultural production, due to the increase in the frequency and intensity of drought. Like many other crops, the grapevine, despite being considered a drought tolerant crop, is threatened by climate change which can lead to a reduction in yields and grape quality and to the modification of the geographical distribution of the wine-growing areas. Multiple mechanisms and responses to counteract the negative effects of the water deficit are put in place by grapevine. Stomatal regulation, osmoregulation, reduction of growth and modification of xylem architecture are some of these acclimations. To support the adoption of strategies and actions in vineyard to face drought, the study of these mechanisms and responses is crucial. The purpose of this thesis fits into this context. In particular, it aims to contribute to the understanding and verifying any involvement of structural anatomical characters of the xylem or of non-structural carbohydrates (NSCs) in the response to the water deficit, in different Vitis vinifera cultivars. To this end, this thesis envisaged the design and implementation of experiments in which modulation of the NSCs content and the eventual relationship of this with other variables (i.e., xylem anatomy, degree of embolism, growth) were investigated by imposition of water deficit with variable intensity and duration. What emerged from this work is that in young potted plants of Vitis vinifera, there is a NSCs-mediated response to short and severe drought stress, although there are slight differences between cultivars with different hydraulic behaviors (i.e., isohydric and anisohydric). The accumulation of low molecular sugars in the period of stress could represent an acclimation strategy carried out by the grapevine with a potential role of osmoregulation, and / or refilling and / or energetic support, consistently with what proposed by other authors. The response to drought stress in anisohydric cultivars would also involve short-term anatomical modifications at the xylem level (i.e., reduction of the lumen of the newly produced tracheary elements) and a recovery mechanism of embolized vessels that could be driven by a possible thickening of the wall due to the adhesion of hygroscopic aqueous gels mediated by maltose-maltodextrin accumulation. The involvement of NSCs as osmo-compatible solutes has been blurred in the case of less intense and more lasting drought stress, where decrease of plant growth appears to be the key adaptive mechanism.