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 Eunice A. Bacelar * , Dario L. Santos, Jose ´ M. Moutinho-Pereira, Berta C. Gonc ¸alves, Helena F. Ferreira, Carlos M. Correia Centre for Technological, Environmental and Life Studies (CETAV), Department of Biological and Environmental Engineering, University of Tra ´s-os-Montes e Alto Douro, Apartado 1013, 5000 Vila Real, Portugal Received 28 July 2005; received in revised form 19 October 2005; accepted 21 October 2005 Available online 15 November 2005 Abstract Changes in anatomy, sclerophylly, pressure–volume relationships, chemical composition and oxidative stress symptoms were studied in leaves of three Olea europaea L. cultivars (Cobranc ¸osa, Madural and Verdeal Transmontana), submitted to contrasting water availability regimes. Anatomically, Cobranc ¸osa and Madural were more capable than Verdeal Transmontana to copewith low water (LW) availability, with a thicker upper epidermis, a thicker palisade parenchyma and a higher stomatal density. Cobranc ¸osa leaves also revealed the lowest specific leaf area and the highest density of the foliar tissue. Under LW conditions, Cobranc ¸osa 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, Cobranc ¸osa 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. # 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Elastic and osmotic adjustment; Leaf anatomy; Lipid peroxidation; Olea europaea L.; Oxidative stress; Water availability 1. Introduction Olive (Olea europaea L.) is a schlerophyllous evergreen tree with a high degree of drought tolerance [1]. The olive ability to acclimate to water availability includes alterations at leaf level, associated with morphological, anatomical and physiological characteristics. Olive cultivars well adapted to drought-field conditions reveal enhanced sclerophylly, with high density of the foliar tissue and the presence of thick cuticle and trichome layers [2]. Adaptations to water availability also involve changes in foliar chemistry. Lowering the osmotic potential due to the accumulation of compatible solutes in the cytoplasm is a well-established ecophysiological mechanism whereby many plants adjust to low soil water availability [3,4]. On the other hand, changes in cell wall elasticity can also contribute to turgor maintenance under drought conditions [5]. Upon mild and moderate water deficit conditions, photo- synthesis decreases in olive plants mainly due to stomatal closure [6]. However, as the stress progresses, biochemical constraints may limit the photosynthetic CO 2 fixation more directly [7]. The limitation of CO 2 assimilation in water- stressed plants causes the over-reduction of photosynthetic www.elsevier.com/locate/plantsci Plant Science 170 (2006) 596–605 Abbreviations: Car, total carotenoids; Chl (a+b) , total chlorophyll; D, leaf tissue density; LW, plants under low water availability; OA, osmotic adjust- ment; ROS, reactive oxygen species; RWC, relative water content; RWC TLP , relative water content at turgor loss point; S, succulence; –SH, total thiols; SLA, specific leaf area; SP, total soluble proteins; SS, total soluble sugars; TBARS, total thiobarbituric acid reactive substances; TM/DM, leaf turgid mass/dry mass ratio; TP, total phenols; WCS, water content at saturation; WSD, water saturation deficit; WW, well-watered plants; e MAX , maximum bulk modulus of elasticity; CP FT , osmotic potential at full turgor; CP TLP , osmotic potential at turgor loss point * Corresponding author. Tel.: +351 259 350740; fax: +351 259 350266. E-mail address: areale@utad.pt (E.A. Bacelar). 0168-9452/$ – see front matter # 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2005.10.014