To dissect differences in both lipid accumulation and composition and the role of these modifications during drought stress, four grapevine cultivars exhibiting differential tolerance to drought were subjected to water shortage. Tolerant cultivars, Kahli Kerkennah and Cardinal, exhibited higher leaf water potential (Ψ w ), and lower lipid peroxidation compared to the sensitive cultivars Guelb Sardouk and Superior Seedless during stress. Total lipid amounts increased during stress only in the leaves of the tolerant cultivars. Drought induced increases in the ratios digalactosyldiacylglycerol/monogalactosyldiacylglycerol and phosphatidylcholine/phoshatidylethanolamine of almost all the drought stressed cultivars. Moreover, the overall analysis of the composition of fatty acids revealed that a linolenic acid was prevalent in grapevine and the unsaturation level of lipids increased under water stress in all the cultivars. Specific adjustments in the lipid composition during stress could compromise stress tolerance.

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Homeostasis of reactive oxygen species (ROS) in the intracellular compartments is of critical importance as ROS have been linked with nearly all cellular processes and more importantly with diseases and aging. PAs are nitrogenous molecules with an evolutionary conserved role in the regulation of metabolic and energetic status of cells. Recent evidence also suggests that polyamines (PA) are major regulators of ROS homeostasis. In Arabidopsis the backconversion of the PAs spermidine (Spd) and spermine to putrescine and Spd, respectively, is catalyzed by two peroxisomal PA oxidases (AtPAO). However, the physiological role of this pathway remains largely elusive. Here we explore the role of peroxisomal PA backconversion and in particular that catalyzed by the highly expressed AtPAO3 in the regulation of ROS homeostasis and mitochondrial respiratory burst. Exogenous PAs exert an NADPH-oxidase dependent stimulation of oxygen consumption, with Spd exerting the strongest effect. This increase is attenuated by treatment with the NADPH-oxidase blocker diphenyleneiodonium iodide (DPI). Loss-of-function of AtPAO3 gene results to increased NADPH-oxidase-dependent production of superoxide anions (O2•− ), but not H2O2, which activate the mitochondrial alternative oxidase pathway (AOX). On the contrary, overexpression of AtPAO3 results to an increased but balanced production of both H2O2 and O2•− . These results suggest that the ratio of O2•− /H2O2 regulates respiratory chain in mitochondria, with PA-dependent production of O2•− by NADPH-oxidase tilting the balance of electron transfer chain in favor of the AOX pathway. In addition, AtPAO3 seems to be an important component in the regulating module of ROS homeostasis, while a conserved role for PA backconversion and ROS across kingdoms is discussed.

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<p style="text-align: justify;"><strong>Aims</strong>: The responses of two Vitis vinifera cultivars (Cardinal and Superior Seedless) and two rootstocks (110R and SO4) to drought, the effect of grafting and the interactions of scion/rootstock were investigated.</p><p style="text-align: justify;"><strong>Methods and results</strong>: The vines were subjected to a progressive water stress in greenhouse controlled conditions. At the end of the water stress treatments, physiological analyses were carried out (stem water potential, dry matter production, soluble sugars, proline as well as ions Na+ and K+). Drought was expressed by the drop of the stem water potential in the stressed vines as compared to their controls. Furthermore, tolerance and sensitivity were linked to the accumulation of soluble sugars and proline as well as the equilibrium of K+ and Na+ in the leaves.</p><p style="text-align: justify;"><strong>Conclusion</strong>: When ungrafted, Cardinal was more tolerant to water stress than Superior Seedless. The grafted vines exhibited more vigour, moreover, the combination of Cardinal with SO4 and Superior Seedless with 110R revealed to be the advantageous associations under water stress.</p><p style="text-align: justify;"><strong>Significance and impact of study</strong>: This work has been carried out to investigate the differential responses of grapevine cultivars to drought stress and the impact of grafting under water shortage conditions.</p>

Salinity is one of the most important abiotic stresses, especially in arid regions. Such devastating constraint is converted mainly to oxidative burst. Thus, plants have to develop strategies to scavenge salt-related regenerated oxidant molecules. In the present work, fully aged plants derived from two Vitis vinifera L. cultivars, the Tunisian autochthonous tolerant genotype Razegui and the salt sensitive Syrah, were analyzed regarding their short term response to 100 mM NaCl, in hydroponic cultures.The ratio [ASA/ASA ? DHA] was calculated on the basis of the oxidation of ascorbic acid (ASA) into dehydroascorbic acid (DHA) in leaves. Results proved that oxidative stress was generated. This led to the accumulation of malondialdehyde which referred to a lipid peroxidation mainly in the sensitive Syrah. In order to cope with these oxidative disturbances, trans-resveratrol as well as its glucosides trans-piceid and cis-piceid have been de novo synthesized in the sensitive variety. Razegui stilbene concentrations were presented here for the first time and unexpectedly did not show a very important variation during the salt elicitation.

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