不同生育期玉米叶片光合特性及水分利用效率对水分胁迫的响应

利用大型移动防雨棚开展了玉米水分胁迫及复水试验,通过分析玉米叶片光合数据,揭示了不同生育期水分胁迫及复水对玉米光合特性及水分利用效率的影响。结果表明:水分胁迫导致玉米叶片整体光合速率、蒸腾速率和气孔导度下降以及光合速率日变化的峰值提前;水分胁迫后的玉米叶片蒸腾速率、光合速率和气孔导度为适应干旱缺水均较对照显著下降,从而提高了水分利用效率,缩小了与水分充足条件下玉米叶片的水分利用效率差值;在中度和重度水分胁迫条件下,玉米叶片的水分利用效率降幅低于光合速率、蒸腾速率和气孔导度的降幅, 有时甚至高于正常供水条件下的水分利用效率;适度的水分胁迫能提高玉米叶片的水分利用效率,从而增强叶片对水分的利用能力,抵御干旱的逆境;水分亏缺对玉米光合速率、蒸腾速率及水分利用效率的影响具有较明显滞后效应,干旱后复水,光合作用受抑制仍然持续;水分胁迫时间越长、胁迫程度越重,叶片的光合作用越呈不可逆性;拔节-吐丝期水分胁迫对玉米叶片光合作用的逆制比三叶-拔节期更难恢复。     

Role of nitric oxide dependence on nitric oxide synthase-like activity in the water stress signaling of maize seedling

Nitric oxide (NO) has been known as an important signal in plant antioxidative defense but its production and roles in water stress are less known. The present study investigated whether NO dependence on a NO synthase-lika (NOS) activity is involved in the signaling of drought-induced protective responses in maize seedlings. NOS activity, rate of NO release and drought responses were analyzed when NO donor sodium nitroprusside (SNP), NO scavenger c-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramathylimidazoline-1-oxyl-3-oxide) and NOS inhibitor L-NAME (NG-nitro-L-arginine methyl ester) were applied to both detached maize leaves and whole plants. Both NOS activity and the rate of NO release increased substantially under dehydration stress. The high NOS activity induced by c-PTIO as NO scavenger and NO accumulation Inhibited by NOS inhibitor L-NAME In dehydration-treated maize seedlings Indicated that most NO production under water deficit stress may be generated from NOS-like activity. After dehydration stress for 3 h, detached maize leaves pretreated with NO donor SNP maintained more water content than that of control leaves pretreated with water. This result was consistent with the decrease in the transpiration rate of SNP-treated leaves subjected to drought treatment for 3 h. Membrane permeability, a cell injury index, was lower in SNP-trested maize leaves under dehydration stress for 4 h when compared with the control leaves. Also, superoxide dismutsse (SOD) activity of SNP combined drought treatment maize leaves was higher than that of drought treatment alone, indicating that exogenous NO treatment alleviated the water loss and oxidative damage of maize leaves under water deficit stress. When c-PTIO as a specific NO scavenger was applied, the effects of applied SNP were overridden. Treatment with L-NAME on leaves also led to higher membrane permeability, higher transpiration rate and lower SOD activities than those of control leaves, indicating that NOS-like activity was involved in the antioxidative defense under water stress. These results suggested that NO dependence on NOS-like activity serves as a signaling component in the induction of protective responses and is associated with drought tolerance in maize seedlings.     

超旱生植物——珍珠的形态解剖和水分生理特征

一、珍珠的形态 珍珠(Salsola passerina),又名珍珠猪毛菜、雀猪毛菜,为藜科猪毛菜属植物,属亚洲中部特有成分(中国植被编辑委员会编著,1980)。小半灌木,株高15—30厘米,多为20厘米左右。茎粗壮,分枝多,呈丛状生长(图版Ⅰ:1);老枝灰褐色,幼枝黄褐色。肉质叶,小,长2.5—3毫米,宽约2毫米,呈锥形或三角形;穗状花序,着生于枝条上部,花小,     

硅对干旱胁迫下玉米水分代谢的影响

利用盆栽试验研究了施硅(K2SiO3)对玉米植株水分代谢的影响.结果表明:施硅降低了干旱胁迫下玉米植株的气孔导度,降低了干旱胁迫早期到中期的蒸腾速率,保持了干旱胁迫后期较高的蒸腾速率,从而导致施硅玉米植株的叶片含水量和水势高于对照.由于植株的水分状况改善,施硅玉米植株生物量高于对照.硅增强玉米植株的抗旱性,而提高植株保水能力是硅提高抗旱性的重要原因.     

Effects of drought on non-mycorrhizal and mycorrhizal maize: changes in the pools of non-structural carbohydrates, in the activities of invertase and trehalase, and in the pools of amino acids and imino acids

To study the response of non-mycorrhizal and mycorrhizal maize plants to drought, the changes in the pools of non-structural carbohydrates and amino acids were analysed in leaves and roots of two maize cvs. Plants well colonized by the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) (60% of root length infected) and comparable non-mycorrhizal plants were subjected to moderate drought stress by reducing the water supply. This stress induced a conspicuous increase in the trehalose pool in the mycorrhizal roots, probably because it was accumulated by the fungal symbiont. Furthermore, glucose and fructose were accumulated in leaves and roots of non-mycorrhizal plants but not in the mycorrhizal ones. Starch disappeared completely from the leaves of both mycorrhizal and non-mycorrhizal plants in response to drought. Activities of soluble acid invertase and trehalase were also measured. Acid invertase activity increased during drought in the leaves of both non-mycorrhizal and mycorrhizal plants whilst in the roots it was unaffected in non-mycorrhizal plants and decreased in the mycorrhizal ones. Without drought stress, trehalase activity was considerably higher in the leaves and roots of mycorrhizal plants than in those of non-mycorrhizal plants. It increased conspicuously during drought, primarily in the leaves of non-mycorrhizal plants. A drought-induced accumulation of amino acids as well as imino acids was found in roots and leaves of both mycorrhizal and non-mycorrhizal plants; leaves of mycorrhizal plants accumulated more imino acids than those of non-mycorrhizal ones. Our results show that drought stress and the presence of a mycorrhizal fungus have a considerable effect on carbon partitioning, imino acid and amino acid accumulation in maize plants.     

Does the rate of German chamomile growth and development influence the response of plants to soil drought?

The response of the wild type (WT) and a strain C6/2 of German chamomile to 7-d soil drought and subsequent 7-day rehydration was studied. Shoot and leaf growth, vegetative development, water and protein contents, ascorbate peroxidase activity and gas exchange were compared. At the stress stage, water content of WT plants was slightly influenced and the effect was ceased after rehydration. Also the decrease in gas exchange was temporary. New leaves were formed, although their area was diminished. On the contrary, leaves of C6/2 plants were more desiccated and the durable decrease in water content was accompanied by the impairment in gas exchange also at the recovery stage (20–40% loss when compared to the control). At both stages of the experiment the growth of the long shoots of this genotype was drastically decreased, as well as leaf formation. Ascorbate peroxidase activity was increased by drought in leaves of both genotypes, but the pattern of changes in WT plants reflected the enhancement of metabolism resulting from proper water content and gas exchange at the recovery stage. Different pattern of changes in the protein content during drought was also noticed: a slight increase in WT, while the decrease by ¼ in C6/2 leaves. The response of WT plants to desiccation and rewatering was found to be more elastic than that of C6/2.     

堇菜叶片草酸钙晶体与水分维持的关系

随着全球气候变化加重,干旱强度和持续时间逐渐增加,严重影响植物生长和作物产量。喀斯特为典型的干旱和高钙生境,植物叶片富集大量的草酸钙晶体,而该晶体与植物耐旱性之间的关系并不清楚。该研究以喀斯特适生植物堇菜(Viola verecumda)为材料,土壤进行自然干旱,分析堇菜叶片的草酸钙晶体变化特征与水分之间的关系。结果表明:在土壤自然干旱条件下,堇菜主要通过细胞内束缚水的释放,维持细胞内水分平衡;而在干旱后期,叶片通过关闭气孔,将部分自由水转变为束缚水,防止水分流失。此外,草酸钙晶体的密度与束缚水含量具有极其显著的强正相关线性回归关系(r=0.825 3,P0.000 1),表明草酸钙晶体作为主要的束缚水物质。因此,堇菜植物在耐旱过程中可能协调草酸钙晶体和气孔的生理行为忍耐干旱胁迫。     

干旱胁迫下白桦（Betula plathphylla）实生苗叶片的水分代谢与部分渗透调节物质的变化

在土壤干旱胁迫进程中,白桦实生苗叶片的自然含水量呈下降趋势;相对含水量的总的变化趋势与自然含水量相同;束缚水含量及束缚水/自由水比值显著升高,复水后,三者又重新恢复至正常水平。随着土壤水分逐渐减少,可溶性蛋白质的含量呈现减少趋势,复水后,可溶性蛋白质含量又可恢复至正常水平。白桦实生苗叶片可溶性糖含量增加,复水后可溶性糖含量降至趋于对照水平。     

茄子/番茄嫁接植株的生理特性及其对黄萎病的抗性

以能降低茄子植株黄萎病病情指数的番茄为砧木嫁接茄子,结果表明,嫁接后的茄子植株光合作用速率和根系活跃吸收面积增大;叶片中束缚水／自由水比值增大,水势降低;根系中苯丙氨酸解氨酶(PAL)、根系和叶片中过氧化物酶(POD)活性增强。     

Drought tolerance of juvenile and mature leaves of a deciduous dwarf shrub Vaccinium myrtillus L. in a boreal environment

The difference between drought tolerance of juvenile and mature leaves of the winter-deciduous dwarf shrub bilberry (Vaccinium myrtillus L.) from a northern boreal environment was investigated. It was hypothesised that mature leaves are more drought sensitive than juvenile leaves. Bilberry plants were allowed to dry out by excluding irrigation when leaves were at juvenile and mature stages. Tissue water content decreased at both phenological stages, but the response was more pronounced in the mature leaves. Anthocyanin concentrations increased as the tissue water content decreased, and again this occurred to a greater extent in the mature leaves. Chlorophyll concentrations decreased only marginally at the juvenile stage, while the decrease was significant in the mature leaves. Chlorophyll degradation was enhanced by drought stress. Soluble proteins decreased and protein oxidation increased in the mature leaves, and degradation of oxidised proteins increased in the drought-stressed plants. The results suggest that leaves of bilberry are more sensitive to drought stress at the mature stage, and that drought stress accelerates senescence at the mature stage. The significance of the results is that dry periods during the juvenility of leaves are not as detrimental as they may be later in summer. In addition, the strategy of a winter-deciduous plant is obviously to protect its perennial parts from severe drought by accelerated leaf senescence at the mature stage. Therefore, the deciduous life form may provide an excellent adaptation against drought also in northern ecosystems. The role of anthocyanins in photoprotection under drought stress is also discussed.     

Influence of arbuscular mycorrhizae and Rhizobium on nutrient content and water relations in drought stressed alfalfa

The objective of this research was to study the effect of drought on nutrient content and leaf water status in alfalfa (Medicago sativa L. cv Aragón) plants inoculated with a mycorrhizal fungus and/or Rhizobium compared with noninoculated ones. The four treatments were: a) plants inoculated with Glomus fasciculatum and Rhizobium meliloti 102 F51 strain, (MR); b) plants inoculated with R. meliloti only (R); c) plants with G. fasciculatum only (M); and d) noninoculated plants (N). Nonmycorrhizal plants were supplemented with phosphorus and nonnodulated ones with nitrogen to achieve similar size and nutrient content in all treatments. Plants were drought stressed using two cycles of moisture stress and recovery. The components of total leaf water potential (osmotic and pressure potentials at full turgor), percentage of apoplastic water volume and the bulk modulus of elasticity of leaf tissue were determined. Macronutrient (N, P, K, Ca, S and Mg) and micronutrient (Co, Mo, Zn, Mn, Cu, Na, Fe and B) content per plant were also measured. Leaves of N and R plants had decreased osmotic potentials and increased pressure potentials at full turgor, with no changes either in the bulk modulus of elasticity or the percentage of apoplastic water upon drought conditions. By contrast, M and MR leaves did not vary in osmotic and turgor potentials under drought stress but had increased apoplastic water volume and cell elasticity (lowering bulk modulus). Drought stress decreased nutrient content of leaves and roots of noninoculated plants. R plants showed a decrease in nutrient content of leaves but maintained some micronutrients in roots. Leaves of M plants were similar in content of nutrients to N plants. However, roots of M and MR plants had significantly lower nutrient content. Results indicate an enhancement of nutrient content in mycorrhizal alfalfa plants during drought that affected leaf water relations during drought stress.     

Composition and Distribution of Free Amino Acids in Flatpea (Lathyrus sylvestris L.) as Influenced by Water Deficit and Plant Age

Drought-stressed flatpea (Lathyrus sylvestris L.) plants from8 to 22 weeks old were analysed for nitrogen, soluble proteinand free amino acids. An increase in nitrogen and free aminoacid concentrations and a decrease in soluble protein levelwere observed in roots of plants up to 16 weeks old. The cumulativeconcentration of free amino acids increased with drought stress.Tissue concentrations of 2, 4-diaminobutyric acid (1.6–2.6%of the dry weight) were highest in leaves. Levels increasedsteadily, nearly doubling, in leaves and stems between weeks10 and 16. Levels in drought-stressed leaves were, on average,11.9% higher than those of controls. Estimated concentrationsof a mixture of 4-aminobutyric acid and an unknown amino acidwere highest in stems, increased in this tissue with age andtended to increase in stems and leaves and decrease in rootsin response to water deficit. Levels of the mixture of homoserineand another unidentified amino acid were not influenced by ageor water status of the plants. Root concentrations of asparagine,arginine, glutamine, aspartate, and another prominent, unidentifiedamino acid increased with plant age and reached a peak at thetime of flowering (14 to 18 weeks). Only the concentration ofthe unknown compound was elevated following drought stress.Concentrations of valine, isoleucine, leucine, phenylalanine,and methionine also increased during this period and were elevatedin drought-stressed plants. Proline levels increased with plantage and drought stress, but proline accounted for only about10% of the total free amino acids in the drought-stressed plants. Key words: 2, 4-Diaminobutyric acid, drought, flatpea     

不同灌溉量夏玉米叶绿素含量的高光谱特征及其反演

植物叶绿素含量直接影响其光合作用,并与植物的光谱特征密切相关。以夏玉米为研究对象,采用人工控水方法研究了夏玉米七叶期不同灌溉量下冠层叶绿素含量特征及其与光谱特征之间的关系。结果表明：灌溉量越少,夏玉米叶片叶绿素含量越低,冠层光谱反射率越高,绿峰位置"红移",而红边位置"蓝移"。叶绿素含量与光谱特征参数、植被光谱指数之间存在极显著相关关系,据此建立了冠层叶绿素含量高光谱估算模型,且基于植被指数模型较基于单一光谱特征参数模型模拟效果更好。研究结果可为夏玉米叶绿素含量的快速无损测定以及夏玉米干旱监测提供依据。     

Water use efficiency in the drought-stressed sorghum and maize in relation to expression of aquaporin genes

Zea mays L. is less tolerant to drought than Sorghum bicolor L. In the present study, we investigated the response of both plants to drought stress applied under field conditions by withholding water for 10 d. The plant growth in terms of shoot fresh and dry masses was more severely reduced in maize than in sorghum, consistently with reduction of leaf relative water content. Gas exchange was also more inhibited by drought in maize than in sorghum. The water use efficiency (WUE) of maize fluctuated during the day and in response to the drought stress. In contrast, sorghum was able to maintain a largely constant WUE during the day in the well-watered plants as well as in the stressed ones. Studying the expression of four aquaporin genes (PIP1;5, PIP1;6, PIP2;3, and TIP1;2) revealed that PIP1;5 in leaves and PIP2;3 in roots were highly responsive to drought in sorghum but not in maize, where they might have supported a greater water transport. The expression pattern of PIP1;6 suggests its possible role in CO₂ transport in control but not droughty leaves of both the plants. TIP1;2 seemed to contribute to water transport in leaves of the control but not droughty plants. We conclude that PIP1;5 and PIP2;3 may have a prominent role in drought tolerance and maintenance of WUE in sorghum plants.     

Exogenously applied glycinebetaine enhances seed and seed oil quality of maize (Zea mays L.) under water deficit conditions

A field trial was carried out to appraise up to what extent exogenous application of a potential osmoprotectant, glycinebetaine (GB), could ameliorate the inhibitory effects of shortage of water on maize seed and seed oil composition and oil antioxidant potential. Two maize cultivars, Agaiti-2002 (drought tolerant) and EV-1098 (drought sensitive), were exposed to drought treatments at the vegetative growth stage. Both the maize cultivars used in the present study are being widely cultivated in Pakistan and have been an important source of developing different maize hybrids. Two levels of glycinebetaine (0 or 30 mM) were foliar-applied at the vegetative stage. Water stress reduced the kernel sugar, oil, protein, moisture contents and most of the seed micro- and macro-nutrients analyzed of both maize cultivars, but it increased the contents of seed fiber and ash contents. Among different seed oil un-saturated fatty acids, water stress increased the oil oleic acid contents with a decrease in linoleic acid contents, which resulted in increased oil oleic/linoleic ratio of both maize cultivars. However, no variation was observed in oil stearic and palmitic acid contents due to water stress. A considerable increase in seed oil α-, γ-, δ- and total tocopherols and flavonoids was observed in both maize cultivars. However, oil phenolic content and 1,1′-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging activity decreased. Foliar-applied GB significantly increased the contents of seed sugar, oil, protein, moisture, fiber, ash, GB contents and micro- and macro-nutrients of both maize cultivars under well irrigated and water deficit conditions. Furthermore, exogenous application of GB increased the oil oleic and linoleinic acid contents. All different lipophilic compounds estimated in the seed oil increased due to foliar applied GB. Furthermore, GB also increased seed oil antioxidant activity appraised in terms of oil DPPH free radical scavenging activity. By summarizing the results, it seemed that exogenously applied GB remained in intact form until later stages of growth and counteracted the inhibitory effects of water deficit on seed and seed oil composition similarly of both maize cultivars.     

Foliar Application of Cytokinin Modulates Gas Exchange Features,Water Relation and Biochemical Responses to Improve Growth Performance of Maize under Drought Stress

Improvement of plant performance under drought stress is crucial to sustaining agricultural productivity. The current study investigated the ameliorative effects of foliar-applied kinetin, an adenine-type cytokinin (CK), on growth and gas exchange parameters, water relations and biochemical attributes of maize plants under drought stress. Eighteen-day-old maize plants were subjected to drought by maintaining soil moisture content at 25% field capacity for 8 days followed by foliar application of kinetin at 0, 75, 150 and 225 mg L⁻¹ (CK0, CK75, CK150 and CK225, respectively) to the plants for two-times at the 9-day interval. Results revealed that drought stress markedly reduced stem diameter, dry weight, chlorophyll content, gas exchange parameters and water balance but increased proline, malondialdehyde and soluble sugar contents, electrolyte leakage and senescence in maize leaves. Application of exogenous CK remarkably improved maize performance by modulating growth, gas exchange- and water relation-related parameters in a dose-dependent manner under drought stress. CK225 increased chlorophyll content (by 61.54%), relative water content (by 49.14%), net photosynthesis rate (by 39.94%) and transpiration rate (by 121.36%) and also delayed leaf senescence but decreased internal CO₂ concentration (by 7.38%), water saturation deficit (by 40.40%) and water uptake capacity (by 42.49%) in both well-watered and drought-stressed plants. Nevertheless, CK application considerably decreased electrolyte leakage, proline, malondialdehyde and soluble sugar levels in drought-stressed maize plants, as also supported by heatmap and cluster analyses. Taken together, exogenous CK at proper concentration (225 mg L⁻¹) successfully improved maize performance under drought conditions, thereby suggesting CK application as a useful approach to alleviate drought-induced adverse effects in maize plants, and perhaps in other important crop plants.     

Effects of drought-rewatering-drought on photosynthesis and growth of maize

Aims Our objective was to investigate the responses of maize photosynthesis and growth to repeated drought.Methods Maize seedlings were exposed to different soil water deficit for three weeks, then rewatering for one week, and again to different water deficit for three weeks, to examine the effects of repeated drought on photosynthesis and growth.Important findings After the first water deficit treatments, under severe drought, plant height, total leaf area of individual plant, shoot and root biomass declined significantly, also transpiration rate (T_r), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), net photosynthetic rate (P_n), maximum net photosynthetic rate (A_max), but light compensation point and dark respiration rate increased significantly. Under medium drought, plant height, leaf area, and shoot biomass decreased significantly, but root biomass did not vary, hence, the ratio of roots to shoots (R/S) increased. Moreover, plants did not show significant differences in photosynthetic parameters. After rewatering, photosynthesis and growth rate of plants previously exposed to water deficit could recover to the levels of well-watered plants, but plant height and leaf area did not recover to the levels of the control. When maize were subjected to recurrent drought, plants pre-exposed to medium drought showed no significant difference in plant height, biomass, and photosynthetic parameters, but a significant decrease in leaf area, compared to plants only exposed to second medium drought. Plants pre-exposed to severe drought had significantly higher T_r, G_s, C_i, P_n, A_max, and, apparent quantum yield but significantly lower plant height, leaf area, and biomass than plants without previous exposure. These results indicated that the first severe drought significantly reduced photosynthetic capacity and maize growth, rewatering could recover photosynthesis and growth rate to the levels of well-watered plants, but could not eliminate the adverse influence of the first drought on growth. The first medium drought could stimulate the growth of maize root system and significantly increased R/S, which can enhance maize drought resistance to subsequent repeated drought, and maintain the total biomass in the control level; the first severe drought could enhance maize drought resistance to subsequent repeated drought in the aspect of photosynthesis, but could not compensate for the adverse effect of early drought on plant growth. Hence, in practice, drought hardening should be limited in the level of medium drought, and avoiding severe drought.     

2种玉米幼苗耐旱性生理机制研究

以白种皮(白玉米)和黄种皮(黄玉米)2个玉米栽培品种为材料,在水培条件下进行聚乙二醇(PEG-6000)模拟干旱胁迫处理,分析玉米叶片抗旱性相关生理特性和质膜H+-ATP酶活性的变化,探讨2种玉米幼苗耐旱性生理机制。结果表明:(1)在2%、5%、10%PEG-6000处理条件下,随处理浓度和时间的增加,2种玉米幼苗植株失水率上升,叶片蒸腾速率降低,气孔传导率下降;在所有相同处理条件下,白玉米植株失水率明显小于黄玉米,而叶片蒸腾速率和气孔传导率下降幅度明显大于黄玉米,即白玉米的耐旱性比黄玉米强。(2)在相同浓度PEG-6000处理下,白玉米叶片可溶性蛋白、可溶性糖含量、游离脯氨酸含量均高于黄玉米,它在干旱胁迫下的渗透调节能力强于黄玉米。(3)在抗氧化酶体系中,随着PEG-6000胁迫浓度的升高,2种玉米叶片CAT活性呈下降趋势,但白玉米CAT活性在2%和5%PEG-6000胁迫下均显著高于黄玉米,其叶片中H2O2含量显著低于黄玉米。(4)随着PEG-6000胁迫浓度的升高,白玉米叶片质膜H+-ATPase磷酸化水平及其与14-3-3蛋白的结合受到的抑制作用比黄玉米强,白玉米叶片质膜H+-ATPase活性比黄玉米叶片低,叶片气孔开度小于黄玉米,叶片蒸腾速率和气孔传导率均低于黄玉米,这可能是白玉米耐旱性强于黄玉米的一个重要机制。     

Salicylic acid pretreatment induces drought tolerance and delays leaf rolling by inducing antioxidant systems in maize genotypes

Salicylic acid (SA) acts as an endogenous signal molecule responsible for inducing abiotic stress tolerance in plants. In this study, the role of SA in improving drought tolerance in two maize cultivars (Zea mays L.) differing in their tolerance to drought was evaluated. The plants were regularly watered per pot and grown until the grain filling stage (R2) under a rainout shelter. At stage R2, parts of the plants were treated with SA, after which drought stress was applied. Leaf samples were harvested on the 10th and 17th days of the drought. Some antioxidant enzyme activity, such as the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content, was measured during the drought period. Exogenous SA prevented water loss and delayed leaf rolling in comparison with control leaves in both cultivars. As a consequence of drought stress, lipid peroxidation, measured in terms of malondialdehyde content, was prevented by SA. SA pretreatment induced all antioxidant enzyme activities, and to a greater extent than the control leaves, during drought. SA also caused a reduction in the ascorbate (ASC) and glutathione (GSH) content in two maize cultivars. The H₂O₂ level was higher in SA pretreated plants than the controls in both cultivars. Pretreatment with SA further enhanced the activities of antioxidant enzymes and the concentrations of non-enzymatic antioxidants in the tolerant cultivar compared with the sensitive cultivar. Results suggested that exogenous SA could help reduce the adverse effects of drought stress and might have a key role in providing tolerance to stress by decreasing water loss and inducing the antioxidant system in plants with leaf rolling, an alternative drought protection mechanism.     

Sorbitol and NaCl stresses affect free, microsome-associated and thylakoid-associated polyamine content in Zea mays and Phaseolus vulgaris

Most of commercially important crops, including maize and common bean, are sensitive to water deficit and salinity. Polyamines are considered to be osmotic and salt tolerance modulators and biochemical indicators of these stresses. In the present study, we measured organ-specific changes in levels of free, microsome- and thylakoid-associated polyamines in leaves and roots of maize and common bean plants exposed for 24 h to osmotic and saline stresses. Putrescine levels were generally higher in the studied organs of both species and under both stresses; only in the roots of salt-treated bean it considerably decreased. In both species, salt stress (200 mM NaCl) induced a significant decrease in free spermidine in roots. We observed a significant decrease in the contents of all polyamines associated with the microsomes isolated from the roots of maize and bean growing in sorbitol and salt conditions. Also the microsomes isolated from the leaves of stressed plants were characterized by the lower contents of polyamines. Our data showed a reduction of putrescine content, with significantly decreased spermidine and spermine levels in thylakoids isolated from the chloroplasts of maize and bean plants growing under both stresses. The results indicate that the studied maize and bean cultivars are rather drought-sensitive. Additionally, microsome- and thylakoid-associated polyamines seem to be good markers of plant stress tolerance.