Background and Aims:The aim of this study was to evaluate differences in adaptive responses in grapevines (Vitis vinifera L. cv Soultanina) exposed to either drought, enhanced ultraviolet-B (UV-B) radiation or the combination of the two environmental stresses. Methods and Results: Results indicated pronounced effects on allometric parameters in plants exposed to the enhanced UV-B radiation. The combined application of drought and enhanced UV-B radiation considerably affected shoot growth rate and leaf dry weight. Guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), superoxide dismutase (SOD, 1.15.1.1) and catalase (CAT, 1.11.1.6) activities increased significantly in the enhanced UV-B radiation treatment. Drought resulted in a significant increase in proline concentration, while the exposure of plants to enhanced UV-B radiation resulted in the production of UV-B absorbing compounds (UVabs). Conclusions: Under drought conditions proline accumulation seemed to be the main mechanism of adaptation contributing to plant's antioxidant defence. On the other hand, under enhanced UV-B radiation, the accumulation of the UV-B absorbing compounds and the increase in antioxidant enzymes activities constitute the main mechanisms of grapevine adaptation. Significance of the Study: The data obtained indicate the occurrence of two different mechanisms of adaptation in response to the stressor applied. Furthermore, the patterns of proline and UVabs concentration changes under stress conditions suggest that the biosynthesis of these two compounds might follow competing metabolic pathways.

No abstract

No abstract

A comparative study on stomatal control between two grapevine varieties (Vitis vinifera L. cvs Sabatiano and Mavrodafni) differing in their ability for drought adaptation was conducted using 3-year-old own-rooted plants. The plants were subjected to prolonged drought stress by withholding irrigation water. The relationship between predawn water potential and maximum stomatal conductance indicated significant differences in stomatal sensitivity to drought between the two varieties. Stomatal closure occurred at higher values of predawn water potential in Sabatiano compared with Mavrodafni. No significant differences were found in plant hydraulic conductance and osmotic potential at full turgor (π100) between the two varieties. Leaf and root ABA concentrations increased more rapidly in Mavrodafni compared with Sabatiano at the beginning of the drought period. Furthermore, Mavrodafni also exhibited significantly higher xylem pH values as well as higher stomatal sensitivity to ABA and pH increase compared with Sabatiano. Results suggest that these two grapevine varieties might have evolved different strategies in order to adapt under drought conditions. In particular, the greater ability for drought adaptation in Sabatiano might be attributed to the more efficient regulation of stomatal closure. In contrast, chemical signalling in Mavrodafni seems to be the main mechanism for drought adaptation.

Differences in abscisic acid (ABA) accumulation between two olive cultivars were studied by enzymelinked immunosorbent assay in roots and leaves, leaf water potential (W l ), stomatal conductance (g s ) as well as photosynthetic rate (A) were also determined in well-watered (WW) and water-stressed (WS) plants of two olive cultivars 'Chemlali' and 'Chetoui'. 'Chemlali' was able to maintain higher leaf CO 2 assimilation rate and leaf stomatal conductance throughout the drought cycle when compared with 'Chetoui'. Furthermore, leaf water potential of 'Chemlali' decreased in lower extent than in Chetoui in response to water deficit. Interestingly, significant differences in water-stress-induced ABA accumulation were observed between the two olive cultivars and reflect the degree of stress experienced. Chemlali, a drought tolerant cultivar, accumulated lower levels of ABA in their leaves to regulate stomatal control in response to water stress compared to the drought sensitive olive cultivar 'Chetoui' which accumulated ABA in large amount.