Exogenous paraquat changes antioxidant enzyme activities and lipid peroxidation in drought-stressed cucumber leaves

In order to examine whether paraquat modifies the functioning of antioxidants and oxidative stress levels in drought-stressed plants, a cucumber cultivar (Cucumis sativus cv. Yuexiu no. 3) was grown hydroponically for 2 days. Drought stress, which was induced by polyethylene glycol (PEG), increased the contents of malonaldehyde (MDA), superoxide radical (O₂⁻) and hydrogen peroxide (H₂O₂) in cucumber leaves, while pretreatment of paraquat decreased them. Under drought stress induced by PEG, we observed the decreased contents of MDA, H₂O₂ and O₂⁻ in paraquat-pretreated plants in comparison to unpretreated stressed plants. Drought stress and paraquat both increased the activities of antioxidants such as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), monodehydroascorbate reducatase (MDHAR, EC 1.6.5.4), glutathione reductase (GR, EC 1.6.4.2), reduced glutathione (GSH) and reduced ascorbate (AsA). But the combined effect of paraquat application and drought stress resulted in the highest activities of antioxidants. So paraquat is able to moderate the activities of scavenging system enzymes and to influence oxidative stress intensity under drought stress induced by PEG.     

Hydrogen peroxide pretreatment alters the activity of antioxidant enzymes and protects chloroplast ultrastructure in heat-stressed cucumber leaves

To elucidate the physiological mechanism of heat stress mitigated by exogenous hydrogen peroxide (H₂O₂) further, seedlings of Cucumis sativus cv Lvfeng no. 6 were subjected to two temperatures (42/38 and 25/18 °C) after pretreatment with 1.5 mM H₂O₂. We investigated whether exogenous H₂O₂ could protect chloroplast ultrastructure under heat stress (42/38 °C) and whether the protective effect was associated with the regulation of antioxidant enzymes. The heat condition disintegrated the membranes of 71.4% chloroplasts in the leaf cells and resulted in the elevated levels of malondialdehyde (MDA) and endogenous H₂O₂. When H₂O₂ pretreatment was combined with the heat stress, the abnormal chloroplasts occurred at a rate of 33.3%, and the contents of MDA and endogenous H₂O₂ were decreased. Heat stress and exogenous H₂O₂ both increased the activities of antioxidant enzymes such as glutathione peroxidase (GSH-Px, EC 1.11.1.9), dehydroascorbate reductase (DHAR, EC 1.8.5.1), monodehydroascorbate reducatase (MDHAR, EC 1.6.5.4), and glutathione reductase (GR, EC 1.6.4.2). The combined effect of heat stress and H₂O₂ pretreatment led to higher activity of antioxidant enzymes including superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), GSH-Px, DHAR, MDHAR and GR in comparison to the heat treatment alone. We propose that exogenous H₂O₂ increases antioxidant enzyme activities in cucumber leaves, decreases lipid peroxidation, and thus protects the ultrastructure of chloroplasts under heat stress.     

Ascorbate levels and the activity of key enzymes in ascorbate biosynthesis and recycling in the leaves of 22 Chinese persimmon cultivars

The objective of this study was to determine diversities of ascorbic acid (AsA) and activities of enzymes involved in AsA metabolism, and to determine their relationships to AsA content in the leaves of Chinese persimmon (Diospyros kaki) cultivars. Results showed that there were huge differences not only in the contents of AsA and glutathione (GSH) but also in the enzyme activities of l-galactono-1,4-lactone dehydrogenase (GLDH, EC 1.3.2.3), dehydroascorbate reductase (DHAR, EC 1.8.5.1), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) in the leaves of 22 Chinese persimmon cultivars. Control of AsA levels mainly depended on the capacity for biosynthesis and GLDH activity played a main role in determining AsA levels in the leaves of persimmon. Both MDHAR and DHAR, MDHAR in particular, also played an important role in maintaining AsA redox state by reducing oxidized AsA back to AsA. But contents of GSH and hydrogen peroide (H₂O₂) and activity of APX were not significantly correlated with AsA content in the leaves of persimmon.     

Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Induction of disease resistance and ROS metabolism in navel oranges by chitosan

The objective of this work was to evaluate how disease resistance and reactive oxygen species (ROS) metabolism in harvested navel oranges (Citrus sinensis L. Osbeck) may be affected by chitosan. Fresh navel oranges were treated with 2% chitosan or 0.5% glacial acetic acid (control) solution for 1 min, and some were inoculated with Penicillium italicum and Penicillium digitatum. Then, the fruit were stored at 20 °C and 85–95% RH. Treatment with 2% chitosan significantly reduced the disease incidence and the lesion diameter compared with control fruit. This treatment effectively enhanced the activities of peroxidase (POD) and superoxide dismutase (SOD), and levels of glutathione (GSH) and hydrogen peroxide (H₂O₂), inhibited the activities of catalase (CAT) and the decreases of ascorbate (AsA) content during navel orange fruits storage. Ascorbate peroxidase (APX) activity in the navel orange fruit was induced slightly by the chitosan treatment during 14–21 days storage. However, glutathione reductase (GR) activity in the fruit was not enhanced by the chitosan treatment. These results indicated that chitosan treatment could induce the navel orange fruit disease resistance by regulating the H₂O₂ levels, antioxidant enzyme and ascorbate–glutathione cycle.     

Effect of brassinosteroids on drought resistance and abscisic acid concentration in tomato under water stress

The effect of brassinosteroid (BR) on relative water content (RWC), stomatal conductance (g_s), net photosynthetic rate (PN), intercellular CO₂ concentration (Ci), lipid peroxidation level, activities of antioxidant enzymes and abscisic acid concentration (ABA) in tomato (Lycopersicon esculentum) seedlings under water stress was investigated. Two tomato genotypes, Mill. cv. Ailsa Craig (AC) and its ABA-deficient mutant notabilis (not), were used. Water stress was achieved by withholding water and both the AC and not plants were treated with 1 μM 24-epibrassinolide (EBR) or distilled water as a control. The RWC, g_s, Ci and PN were significantly decreased under water stress. However, EBR treatment significantly alleviated water stress and increased the RWC and PN. EBR application also markedly increased the activities of antioxidant enzymes (catalase, ascorbate peroxidase and superoxide dismutase) while it decreased g_s, Ci and the contents of H₂O₂ and malondialdehyde (MDA). Interestingly, ABA concentration in AC and not plants was markedly elevated after EBR treatment although the increasing rate and amplitude of ABA in not plants treated by EBR was significantly lower than those in AC plants. Our study suggested that amelioration of the drought stress of tomato seedlings may be caused by EBR-induced elevation of endogenous ABA concentration and/or the activities of antioxidant enzymes.     

Stimulation of ROS-scavenging systems in squash (Cucurbita pepo L.) plants by compost supplementation under normal and low temperature conditions

The beneficial effect of compost, the final product of aerobic biodegradation of organic matter, on growth, lipid peroxidation [as malondialdehyde (MDA], hydrogen peroxide (H₂O₂) and superoxide anion (O₂^•−), activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), as well as reduced ascorbate (ASC) and glutathione (GSH) and their oxidized forms was investigated in squash (Cucurbita pepo L. cv. Eskandarany) plants exposed to normal and low temperature (LT) conditions. LT stress of 8 °C significantly reduced the plant growth of untreated plants, but compost alleviated the adverse effect of stress and significantly increased the fresh and dry weights under normal and stress conditions. LT also induced accumulation of H₂O₂ and O₂^•− and resulted in increased lipid peroxidation, pointing out to cellular oxidative stress. Under compost application, such reactive oxygen species (ROS) and peroxidized lipids were markedly reduced, but SOD, CAT, APX and GR activities, key enzymes of ROS-scavenging systems, were significantly increased. Data also indicated that there were general reductions in total ascorbate and glutathione pool in LT control plants, but compost-treated ones considerably have maintained higher levels of such redox metabolites. Significantly higher ratios of ASC/DHA (dehydroascorbate) and GSH/GSSG (glutathione disulfide) were generally found in compost-treated plants than in untreated-ones. It is evident that compost induced enhancement of LT tolerance was related to up-regulation of enzymatic and non-enzymatic antioxidant systems. Such enhancement would eventually protect plant cells from LT-induced oxidative stress reactions via scavenging ROS.     

Photosynthetic characteristics and protective mechanisms against photooxidation during high temperature stress in two citrus species

Exposure of Satsuma mandarin (Citrus unshiu Marc.) and Navel orange (Citrus sinensis Osbeck) plants to high temperature (38 °C) led to reductions of the net photosynthetic rate (Pn), the photorespiration rate (Pr), the quantum efficiency CO₂ assimilation (ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$), the maximal photochemical efficiency of PS2 (Fv/Fm), the photochemical quenching (qP) and the quantum efficiency of PS2 photochemistry (Φ_PS2), whereas the minimal fluorescence yield (Fo) and the non-photochemical quenching (qN) increased. Increase in the value of Pr/Pn and ΦPS₂/ΦCO₂${\Phi }_{\text{PS}2}/{\Phi }_{\text{C}{\text{O}}_2}$ was attributed to the greater decrease in Pn and ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$ than Pr and Φ_PS2. In addition, the superoxide radical (O₂⁻) production, the H₂O₂ concentration and the activities of antioxidant enzymes such as the superoxide dismutase (SOD, EC 1.15.1.1), the ascorbate peroxidase (APX, EC 1.11.1.11), the dehydroascorbate reductase (DHAR, EC 1.8.5.1) and the catalase (CAT, EC 1.11.1.6) were raised. On the other hand, the chlorophyll concentration in leaves decreased during high temperature stress. These results suggest that decline in Pn related to inactivation of PS2 reaction centers may be due to the enhanced number of active oxygen species in the citrus leaves. The water–water cycle may play a role in limiting the degree of photodamage caused by high temperature. Lower O₂⁻ production rate, the H₂O₂ concentration and the antioxidant enzymes activity were observed in high temperature tolerant species of citrus. The exogenous active oxygen scavenger ascorbic acid (Asc) enhanced the ability to clear the O₂⁻ in citrus plants, and quicken the recovery of photosynthetic apparatus.     

CaCl_2对NaCl胁迫下酸枣苗AsA-GSH循环的影响

以酸枣(Ziziphus acidojujuba C.Y.Cheng et M.J.Liu)水培实生幼苗为试材,研究了CaCl_2对NaCl胁迫下其根、茎、叶中抗坏血酸—谷胱甘肽循环(AsA-GSH)的影响。结果表明:与对照(日本园试配方营养液)相比,NaCl处理下根和叶中AsA含量升高,MDHAR活性升高,APX活性下降;根、茎、叶中GSH含量升高。NaCl+CaCl_2处理与NaC处理相比,根和茎中AsA含量进一步升高,叶中AsA含量下降,叶中APX下降,根中MDHAR活性进一步升高,茎和叶中DHAR活性升高;根和叶中GSH含量下降。外源CaCl_2可能通过提高酸枣实生苗根、茎和叶中AsA再生关键酶MDHAR和DHAR活性,促进根和茎中AsA的再生与生物合成,从而提高根、茎清除过量H_2O_2的能力,缓解NaCl胁迫对酸枣幼苗根和茎部的伤害。     

Magnesium deficiency induced oxidative stress and antioxidant responses in mulberry plants

The aim of the study was to implicate induction of oxidative stress and antioxidative responses with the effects of Mg deficiency in mulberry plants. Mulberry (Morus alba L.) cv. Kanva-2 plants grown in hydroponics were subjected to deficiency of Mg. Mg-deficient plants developed visible symptoms—deep interveinal chlorotic mottling and necrosis in the older and middle leaves. The decreases in the dry matter yield of plants and concentrations of sugars and starch in the leaves of Mg-deficient plants are suggestive of decreased photosynthetic activity. Mg-deficiency decreased concentrations of photosynthetic pigments, and increased concentrations of H₂O₂ and ascorbate and activities of antioxidative enzymes—peroxidase (POD), ascorbate peroxidase (APX) and superoxide dismutase (SOD). The results suggest induction of oxidative stress by enhancing generation of ROS and inducing alterations in redox status, accompanied by activation of antioxidant machinery including induction of some new SOD isoforms in Mg-deficient mulberry plants. Despite significant increase in H₂O₂, lipid peroxidation was decreased in Mg-deficient plants.     

青枯雷尔氏菌胁迫对烟草植株抗氧化酶系活性的影响

以青枯雷尔氏菌RS-1403作为外源微生物,研究不同浓度青枯雷尔氏菌胁迫对烟草植株叶片PPO、POD、SOD酶活性的影响。结果表明:PPO和POD酶活性总和显著高于对照,而SOD酶活性总和除了处理2(接种浓度为2.35×10~4CFU/mL)外,其余的各个处理的均低于对照。烟草植株的根部、茎部和叶片的POD、PPO和SOD酶活性总和明显高于对照处理,并且其酶活性达到高峰的时间有所不同。胁迫接种5 d后,烟草植株叶片和茎部的POD酶活性和对照处理的比值最大,胁迫接种10 d后,烟草植株根部POD酶活性比值最大。烟草植株叶片和根部在接种15 d后,PPO酶活性和对照处理的比值达到最大,茎部PPO酶活性在接种5 d后比值最大。接种20 d后,处理烟草植株叶片和茎部的SOD酶活性和对照处理的比值达到最大,接种后25 d,根部SOD酶活性比值最大。     

The response of different almond genotypes to moderate and severe water stress in order to screen for drought tolerance

In order to screen almond genotypes for drought tolerance, three different irrigation levels including moderate and severe stress (Ψs = −1.2 and −1.8 MPa respectively) and a control treatment (Ψs = −0.33 MPa) were applied for five weeks to six different cultivated almond seedlings. A factorial experiment was conducted with a RCBD which included 3 irrigations factors, 6 genotype factors and 3 replications. Seeds were prepared from controlled pollination of the bagged trees (after emasculation and flower isolation using isolator packets in the previous year). Genotypes included: homozygote sweet (Butte), heterozygote sweet (SH12, SH18, SH21 and White) and homozygote Bitter (Bitter Genotype). Leaf and root morphological and physiological traits including; midday relative water content, midday leaf (xylem) water potential, shoot dry weight and growth, total leaf area, leaf size, total leaf dry weight, specific leaf area, leaf greenness (SPAD), stomatal size and density, root and leaf nitrogen content and chlorophyll fluorescence were measured throughout the study. Results showed the six genotypes had different reactions to water stress but all genotypes showed an ability to tolerate the moderate and severe stresses and they showed different degrees of response time to drought stress. Almond seedling leaves could tolerate Ψ_w between −3 and −4 MPa in short periods. Water availability did not significantly affect stomatal density and size of young almond plants. The analysis of leaf anatomical traits and water relations showed the different strategies for almond genotypes under water stress conditions. Although almond seedlings even in severe stress kept their leaves, they showed a reduction in size to compensate for the stress effects. All genotypes managed to recover from moderate stress so Ψ_w = −1.2 could be tolerated well by almond seedlings but Ψ_w = −1.8 limited young plant growth. Leaf greenness, leaf size, shoot growth, shoot DW, TLDW and stomatal density were not good markers for drought resistance in almond seedlings. Root DW/LA, lower stomatal size and lower SLA might be related to drought resistance in cultivated almonds. Butte had the least resistance and White showed better performance during water stress while other genotypes were intermediate. Bitter seedlings showed no superiority in comparison with other genotypes under water stress conditions except for better germination and greater root DW which might make them suitable as rootstocks under irrigation conditions.     

Exogenous CaCl2 reduces salt stress in sour jujube by reducing Na+ and increasing K+, Ca2+, and Mg2+ in different plant organs

In this study, we investigated the effects of 10 mM CaCl₂ on membrane permeability, malondialdehyde (MDA), reactive oxygen species (ROS), and Na⁺, K⁺, Ca²⁺, and Mg²⁺ concentrations in different organs of sour jujube grown under 150 mM NaCl stress. Our results showed 73% leaf wilting in the Na treatment. The Na treatment significantly increased leaf superoxide (O₂^.?) production rates, hydrogen peroxide (H₂O₂) concentrations, cell membrane permeability, MDA concentrations, and Na⁺ concentrations in roots, stems, and leaves. The Na treatment significantly reduced K⁺, Ca²⁺,and Mg²⁺ concentrations in roots, but increased K⁺ concentrations in stems. Compared with the Na treatment, 39% of the leaves showed wilting symptoms in the Na+Ca treatment. The Na+Ca treatment significantly decreased leaf O₂^.? production rates, H₂O₂ concentrations, cell membrane permeability, and MDA concentrations. Moreover, the Na+Ca treatment (1) significantly reduced Na⁺ concentrations in roots, stems, and leaves; (2) significantly increased root K⁺ concentrations; (3) significantly increased K⁺/Na⁺ ratios in roots; (4) significantly increased Ca²⁺ concentrations in stems and leaves, and Mg²⁺ concentrations in roots. In conclusion, exogenous CaCl₂ reduces NaCl stress in sour jujube by reducing Na+ concentrations and increasing K⁺, Ca²⁺, and Mg²⁺ concentrations in various plant organs.     

外源物质对干旱复水平邑甜茶抗氧化酶的影响

以苹果砧木平邑甜茶2a生实生苗为材料进行盆栽试验,研究比较了干旱复水条件下外源甜菜碱(GB)、脱落酸(ABA)和硝普纳(SNP,NO供体)对平邑甜茶幼苗抗氧化防护酶活性的影响。结果表明:外源GB、ABA和NO显著降低了干旱胁迫下平邑甜茶幼苗叶片质膜相对透性和MDA含量,重度胁迫时与CK相比,分别降低了13.5%、12.2%、18.4%与32.4%、14.4%、37.6%;外源GB、ABA和NO提高了叶片中SOD、CAT和POD的活性,在田间持水量30%时分别达到最大,与同期CK相比,POD活性分别增加13.5%、13.4%和24.4%,SOD活性分别增加15.3%、13.7%和16.2%,CAT活性则分别增加63.2%、53.7%和95.3%,之后酶活性开始下降。外源GB、ABA处理后GR、DHAR、APX和MDHAR的变化趋势与CAT等趋势相同,同样在田间持水量30%时酶活分别达到最大;NO处理后,GR、DHAR、APX的变化趋势亦相同,虽然NO对MDHAR活性比干旱处理有所升高,但差异不显著。复水后,不同外源物质下植物的抗旱生理指标变化趋势不尽相同。表明喷施外源GB、ABA和NO可有效的提高叶片的抗氧化系统酶的活性,增强平邑甜茶幼苗的抗旱能力。比较GB、ABA和NO处理,NO在提高平邑甜茶抗旱性方面效果最好,GB处理其次,ABA处理最低。     

Root restriction-induced limitation to photosynthesis in tomato (Lycopersicon esculentum Mill.) leaves

Root restriction often depresses photosynthetic capacity and the mechanism for this reduction, however, remains unclear. To identify the mechanism by which root restriction affects the photosynthetic characteristics, tomato (Lycopersicon esculentum Mill.) seedlings were subjected to root restriction stress with or without supplemental aeration to the nutrient solution. With the development of the root restriction stress, CO₂ assimilation rate was decreased only in confined plants without supplemental aeration. There were also significant decreases in leaf water potential, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and increases in the stomatal limitation (l) and the xylem sap ABA concentration. Meanwhile, the maximum carboxylation rate of Rubisco (V_cmax) and the capacity for ribulose-1,5-bisphosphate regeneration (J_max) also decreased, followed by substantial reductions in the quantum yield of PSII electron transport (Φ_PSII). Additionally, root restriction resulted in accumulation of carbohydrates in various plant tissues irrespective of aeration conditions. It is likely that root restriction-induced depression of photosynthesis was mimicked by water stress.     

Regulation of some biochemical attributes in drought-stressed cauliflower (Brassica oleracea L.) by seed pre-treatment with ascorbic acid

Cauliflower (Brassica oleracea L. var. botrytis) is widely used as a vegetable in many countries; however, productivity is adversely affected in areas affected by drought. To investigate the role of exogenously applied ascorbic acid (AsA) in mitigating the negative effects of drought on cauliflower, a pot experiment was performed using two cultivars of cauliflower ‘Local’ and ‘S-78’. Seeds of both cultivars were soaked in 75 mg l^–1, or in 150 mg l^–1 AsA, or in water (control) for 16 h. Water-deficit stress suppressed plant growth, reduced leaf chlorophyll concentrations, relative water contents (RWC), shoot and root P and K⁺ ion concentrations, and total soluble protein concentrations, significantly. However, significant drought-induced increases were observed in relative membrane permeability (RMP), the accumulation of total phenolic compounds, leaf free proline, glycinebetaine (GB), endogenous AsA, and hydrogen peroxide concentrations, and in the activity of superoxide dismutase (SOD). Seed treatment with 75 or 150 mg l^–1 AsA resulted in lower accumulations of H₂O₂, while increasing shoot and root fresh weights and dry weights, RWC, total phenolic compound, free proline, GB, and endogenous AsA concentrations, and the activities of SOD and catalase (CAT). No changes were observed in leaf chlorophyll concentrations or in peroxidase (POD) activities, RMP, shoot and root P and K⁺ ion accumulation, or in total soluble protein concentrations under water stress or non-stress conditions following seed treatment with AsA. ‘Local’ had higher proline concentrations and SOD activities; however, ‘S-78’ had higher RWC values, GB, and AsA concentrations. Overall, a pre-sowing treatment of cauliflower seed with 75 or 150 mg l^–1 AsA improved seedling tolerance to drought stress in both cultivars, which could be attributed to AsA-induced decreases in RMP and H₂O₂ concentrations, increases in the activities of CAT and SOD, increased RWC, and higher total phenolic compound, proline, GB, and AsA concentrations. The exogenous application of AsA therefore offers an effective strategy to minimise the adverse effects of drought stress on vegetable crops, including cauliflower.     

Response to drought and salt stress of lemon ‘Fino 49’ under field conditions: Water relations,osmotic adjustment and gas exchange

Drought and salinity are two of the most important factors limiting the lemon yield in south-eastern Spain. The effects of drought and salt stress, applied independently, on water relations, osmotic adjustment and gas exchange in the highest evapotranspiration period were studied to compare the tolerance and adaptive mechanisms of 13-year-old ‘Fino 49’ lemon trees, in immature and mature leaves. The study was carried out in an experimental orchard located in Torre Pacheco (Murcia). Three treatments were applied: Control, well-irrigated; drought-stress (DS), non-irrigated from 15th May to 7th July and salinity, irrigated with 30 mM NaCl from 1st March to 7th July. At the end of the experiment, only DS trees showed a decreased leaf stem water potential (Ψ_md). Under DS conditions, both types of leaf lost turgor and did not show any osmotic or elastic mechanism to maintain leaf turgor. Osmotic adjustment was the main tolerance mechanism for maintenance of turgor under salt stress, and was achieved by the uptake of Cl⁻ ions. Gas-exchange parameters were reduced by DS but not by salinity, stomatal closure being the main adaptive mechanism for avoidance of water loss and maintenance of leaf turgor. Salinity gave rise to greater Cl⁻ accumulation in mature than in immature leaves. The increase of proline in immature leaves due to DS indicates greater damage than in mature leaves.