Abstract
Aim: In the Mediterranean region, grapevines usually undergo drought and high UV-B intensities during their summer growth season. The present study was conducted in order to evaluate the effects of these two abiotic stressors on the physiological and biochemical characteristics of a major Greek raisin variety (Vitis vinifera L. cv Soultanina).Methods and results: The experimental plants were three-years-old, grafted onto 110R rootstock and grown outdoors in 25 L pots containing a peat:perlite:sand (3:1:1, v/v/v) potting mixture. Grapevines were subjected to two irrigation treatments: (1) Well-Watered (plants were uniformly irrigated on a daily basis to soil substrate capacity), and (2) Water-Stressed (plants were equally irrigated with 50 % of the amount of water provided to Well-Watered plants), and to two levels of UV-B radiation: (1) ambient UV-B radiation, and (2) ambient plus 15 % UV-B radiation. Although the combination of drought and supplemental UV-B radiation appeared to have synergistic effects on gas exchange characteristics and H2O2 production, the development of biochemical limitations to photosynthesis was not detectable. Compared to the other stress treatments, WW±15 % UV-B plants exhibited higher stomatal conductance (gs) and photosynthetic rate (PN).Conclusion: Under elevated UV-B radiation, superoxide dismutase (SOD) activation, chlorophyll degradation and enhanced synthesis of carotenoids all helped the plant to maintain its physiological functions, while in Water-Stressed plants irrespective of the level of UV-B, a more pronounced role of abscisic acid (ABA) and trans-zeatin-riboside (t-ZR) in mediating stomatal responses was revealed.Significance of the study: Our results imply that the environmental conditions were not stressful enough to report the occurrence of non-diffusional limitations to photosynthesis. In addition, two different adaptive responses in relation to the applied abiotic stressor were shown.
Highlights
Viticulture is an activity of primary socioeconomic importance worldwide; it is present in more than 40 countries, the global vineyard covers an area of 7.4 million hectares, and total production amounts to 77.8 million tonnes of fresh grapes and 292.3 million hectoliteres of wine (OIV, 2019)
Throughout the experimental period, ΨPD values were significantly reduced in accordance with the water supply, while UV-B radiation had no additional effect on leaf water relations (Figure 1B)
The combination of drought and enhanced UV-B radiation (WS ± 15 % UV-B treatment) appeared to have a synergistic effect on gas exchange parameters (Table 1), which is consistent with previous reports (Doupis et al, 2011; Doupis et al, 2016); the simultaneous and parallel decline in photosynthetic rate (PN) and gs values (Figure 1A, 1C), as well as the high Water Use Efficiency (WUE) values (Figure 1D) exhibited by the combined stressors treatment, suggest that photochemical inhibition did not occur and that stomatal closure is the main factor responsible for the reductions in CO2 assimilation
Summary
Viticulture is an activity of primary socioeconomic importance worldwide; it is present in more than 40 countries, the global vineyard covers an area of 7.4 million hectares, and total production amounts to 77.8 million tonnes of fresh grapes and 292.3 million hectoliteres (mhl) of wine (OIV, 2019). Climatic scenarios suggest that a lengthened summer drought, along with a gradual increase in temperature and occurrences of heat waves, will strike the Mediterranean region in the upcoming decades (Stocker, 2013). They predict that Mediterranean plants will be subject to increased solar radiation and, in particular, ultraviolet-B radiation (280-315 nm) levels, due to a reduction in average cloud cover (Bais et al, 2015). Plant water demand will increase, the genotoxic effects of high UV-B doses will be intensified, and grapevines will probably need to activate a variety of defense mechanisms to tolerate the limited water availability and the enhanced levels of ultraviolet radiation
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