The effects of drought and supplemental UV-B radiation on physiological and biochemical traits of the grapevine cultivar “Soultanina”

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.