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The article discusses the role of water availability in plant productivity and yield. It focuses on the measurement of leaf solute potential, which is an indicator of a plant's ability to adapt to heat and drought. The study specifically examines the seasonal changes in solute potential in grapevine cultivars and finds that the seasonal decrease in solute potential is more significant than the differences between cultivars or the response to drought. The findings suggest that solute accumulation is not solely a response to drought, but is also influenced by other factors such as leaf age and atmospheric conditions. The study highlights the importance of considering seasonal osmotic adjustment in improving water use efficiency and soil water conservation strategies. [Extracted from the article]

SUMMARY: The leaf of a deciduous species completes its life cycle in a few months. During leaf maturation, osmolyte accumulation leads to a significant reduction of the turgor loss point (ΨTLP), a known marker for stomatal closure. Here we exposed two grapevine cultivars to drought at three different times during the growing season to explore if the seasonal decrease in leaf ΨTLP influences the stomatal response to drought. The results showed a significant seasonal shift in the response of stomatal conductance to stem water potential (gs~Ψstem), demonstrating that grapevines become increasingly tolerant to low Ψstem as the season progresses in coordination with the decrease in ΨTLP. We also used the SurEau hydraulic model to demonstrate a direct link between osmotic adjustment and the plasticity of gs~Ψstem. To understand the possible advantages of gs~Ψstem plasticity, we incorporated a seasonally dynamic leaf osmotic potential into the model that simulated stomatal conductance under several water availabilities and climatic scenarios. The model demonstrated that a seasonally dynamic stomatal closure threshold results in trade‐offs: it reduces the time to turgor loss under sustained long‐term drought, but increases overall gas exchange particularly under seasonal shifts in temperature and stochastic water availability. A projected hotter future is expected to lower the increase in gas exchange that plants gain from the seasonal shift in gs~Ψstem. These findings show that accounting for dynamic stomatal regulation is critical for understanding drought tolerance. [ABSTRACT FROM AUTHOR]

Water availability is arguably the most important environmental factor limiting crop growth and productivity. Erratic precipitation patterns and increased temperatures resulting from climate change will likely make drought events more frequent in many regions, increasing the demand on freshwater resources and creating major challenges for agriculture. Addressing these challenges through increased irrigation is not always a sustainable solution so there is a growing need to identify and/or breed drought-tolerant crop varieties in order to maintain sustainability in the context of climate change. Grapevine (Vitis vinifera), a major fruit crop of economic importance, has emerged as a model perennial fruit crop for the study of drought tolerance. This review synthesizes the most recent results on grapevine drought responses, the impact of water deficit on fruit yield and composition, and the identification of drought-tolerant varieties. Given the existing gaps in our knowledge of the mechanisms underlying grapevine drought responses, we aim to answer the following question: how can we move towards a more integrative definition of grapevine drought tolerance? [ABSTRACT FROM AUTHOR]

In recent years, the validity of embolism quantification methods has been questioned, especially for long-vesseled plants. Some studies have suggested that cutting xylem while under tension, even under water, might generate artificial cavitation. Accordingly, a rehydration procedure prior to hydraulic measurements has been recommended to avoid this artefact. On the other hand, concerns have been raised that xylem refilling might occur when samples are rehydrated. Here, we explore the potential biases affecting embolism quantification for grapevine (Vitis vinifera L.) petioles harvested under tension or after xylem relaxation. We employ direct visualization of embolism through X-ray micro-computed tomography (microCT) to test for the occurrence of fast refilling (artifactually low per cent loss of conductivity (PLC) due to rehydration prior to sample harvest) as well as excision-induced embolism (artifactually high embolism due to air introduction during harvest). Additionally, we compared the response functions of both stomatal regulation and xylem embolism to xylem pressure (ψx). Short-time (20 min) xylem tension relaxation prior to the hydraulic measurement resulted in a lower degree of embolism than found in samples harvested under native tensions, and yielded xylem vulnerability curves similar to the ones obtained using direct microCT visualization. Much longer periods of hydration (overnight) were required before xylem refilling was observed to occur. In field-grown vines, over 85% of stomatal closure occurred at less negative ψx than that required to induce 12% PLC. Our results demonstrate that relaxation of xylem tension prior to hydraulic measurement allows for the reliable quantification of native embolism in grapevine petioles. Furthermore, we find that stomatal regulation is sufficiently conservative to avoid transpiration-induced cavitation. These results suggest that grapevines have evolved a strategy of cavitation resistance, rather than one of cavitation tolerance (diurnal cycles of embolism and repair). [ABSTRACT FROM AUTHOR]

• Cluster thinning and selective berry thinning significantly increased the accumulation of soluble solids in grapes. • Anthocyanin concentration was increased by both thinning treatments, and a shift in the profile was observed. • As compared to the control, only selective berry thinning promoted a significant reduction of the skin proanthocyanidins. • Both treatments resulted in a reduction of the proanthocyanidins galloylation in skins, but only berry thinning reduced the skin prodelphinidines. 'Refosco dal peduncolo rosso' is a late-ripening and low-yielding red grape variety, mainly cultivated in Northeastern Italy (Veneto and Friuli Venezia Giulia), and characterized by relatively high anthocyanins and average-to-low tannins concentrations. Under Friuli's climatic conditions, it is often challenging to maintain the Refosco dal peduncolo rosso grapes hanging on the vines long enough to match complete berry maturation before the rain season starts. Therefore, winegrowers normally perform cluster thinning in order to enhance or accelerate ripening. This study compared the effects of selective berry thinning (cluster shoulders and tips removal) and classical cluster thinning on fruit technological maturity, anthocyanin profile, and skin and seed proanthocyanidins concentration. Our results revealed that both thinning treatments induced a significant increase in total soluble solids, as well as total anthocyanins through the specific enhancement of OH- and di-substituted monoglucosylated anthocyanins. Additionally, skin high molecular weight proanthocyanidins was reduced by selective berry thinning, while mean degree of polymerization and percentage of galloylation were significantly decreased by both thinning treatments. These results showed that the yield reduction obtained by both methods were profitable to improve the maturation of Refosco dal peduncolo rosso grapes. However, the application of selective berry thinning provided a significant reduction of both skin high molecular weight proanthocyanidins and percentage of prodelphinidins. Therefore, the first evidences on grapes composition favored the cluster thinning technique as less time consuming, but more research on wine and sensory effects is needed to confirm the potential of selective berry thinning. [ABSTRACT FROM AUTHOR]