Immediate responses and adaptative strategies of three olive cultivars under contrasting water availability regimes: Changes on structure and chemical composition of foliage and oxidative damage

Changes in anatomy, sclerophylly, pressure–volume relationships, chemical composition and oxidative stress symptoms were studied in leaves of three Olea europaea L. cultivars (Cobrançosa, Madural and Verdeal Transmontana), submitted to contrasting water availability regimes. Anatomically, Cobrançosa and Madural were more capable than Verdeal Transmontana to cope with low water (LW) availability, with a thicker upper epidermis, a thicker palisade parenchyma and a higher stomatal density. Cobrançosa leaves also revealed the lowest specific leaf area and the highest density of the foliar tissue. Under LW conditions, Cobrançosa and Madural showed greater capability for osmotic adjustment and increased tissue rigidity. By contrast, Verdeal Transmontana did not exhibit osmotic adjustment, but was able to increase tissue elasticity and total soluble protein concentration. Leaves grown under LW conditions revealed signs of oxidative stress, with decreases in chlorophyll, carotenoid and total thiol concentrations and increased levels of lipid peroxidation. Nevertheless, LW plants developed some defense mechanisms against oxidative stress, like the increase in total phenol and total soluble protein concentrations. Comparatively, Cobrançosa revealed more protection against oxidative stress. In opposition, the increased levels of lipid peroxidation and the decreased total thiol concentration under LW conditions suggest that the mechanisms against oxidative stress were less effective in Madural.