UV light and adaptive divergence of leaf physiology, anatomy, and ultrastructure drive heat stress tolerance in genetically distant grapevines

The genetic basis of plant response to light and heat stresses had been unveiled, and different molecular mechanisms of leaf cell homeostasis to keep high physiological performances were recognized in grapevine varieties. However, the ability to develop heat stress tolerance strategies must be further elucidated since the morpho-anatomical and physiological traits involved may vary with genotype × environment combination, stress intensity, and duration. A 3-year experiment was conducted on potted plants of Sardinian red grapevine cultivars Cannonau (syn. Grenache) and Carignano (syn. Carignan), exposed to prolonged heat stress inside a UV-blocking greenhouse, either submitted to low daily UV-B doses of 4.63 kJ m-2 d-1 (+UV) or to 0 kJ m-2 d-1 (-UV), and compared to a control (C) exposed to solar radiation (4.05 kJ m-2 d-1 average UV-B dose). Irrigation was supplied to avoid water stress, and canopy light and thermal microclimate were monitored continuously. Heat stress exceeded one-third of the duration inside the greenhouse and 6% in C. In vivo spectroscopy, including leaf reflectance and fluorescence, allowed for characterizing different patterns of leaf traits and metabolites involved in oxidative stress protection. Cannonau showed lower stomatal conductance under C (200 mmol m-2 s-1) but more than twice the values inside the greenhouse (400 to 900 mmol m-2 s-1), where water use efficiency was reduced similarly in both varieties. Under severe heat stress and -UV, Cannonau showed a sharper decrease in primary photochemical activity and higher leaf pigment reflectance indexes and leaf mass area. UV-B increased the leaf pigments, especially in Carignano, and different leaf cell regulatory traits to prevent oxidative damage were observed in leaf cross-sections. Heat stress induced chloroplast swelling, plastoglobule diffusion, and the accumulation of secretion deposits in both varieties, aggravated in Cannonau -UV by cell vacuolation, membrane dilation, and diffused leaf blade spot swelling. Conversely, in Carignano UV-B, cell wall barriers and calcium oxalate crystals proliferated in mesophyll cells. These responses suggest an adaptive divergence among cultivars to prolonged heat stress and UV-B light. Further research on grapevine biodiversity, heat, and UV-B light interactions may give new insights on the extent of stress tolerance to improve viticulture adaptive strategies in climate change hotspots.

From Field to Waste Valorization: A Preliminary Study Exploring the Impact of the Wine Supply Chain on the Phenolic Profile of Three Sardinian Pomace Extracts

The winemaking process generates an annual global production of about 10 million tons of waste consisting of stalks, skin, and seeds. The possible reutilization of wine pomace is strictly linked to its chemical composition. In this preliminary study, three different Sardinian white grapes (Malvasia, Vermentino and Nasco) grown in the same area were evaluated through a whole wine production chain. To reduce environmental impact, all the grapes were treated following the integrated production practice (IPP) strategies. The adopted agronomic methods and the main physico-chemical parameters of the fresh fruits and musts were evaluated. A fully qualitative and quantitative characterization of the phenolic fraction of the pomace extracts was performed by HPLC-DAD after a post-winemaking process. Water and ethanol were utilized as green solvents in the extraction process. Additionally, the entire pomace post-winemaking process was carried out within the winery facilities to reduce energy loss and road transportation. The findings demonstrated that large amounts of beneficial polyphenols are present in pomace extracts, and that the type of grape used, agronomic practices, and winemaking method all influence the quantity and quality of the extracts. The polyphenol concentrations in the Vermentino (28,391.5 ± 7.0 mg/kg) and Malvasia pomace (11,316.3 ± 6.5 mg/kg) were found to be the highest and lowest, respectively.