Growth characteristics and proline content in relation to water status in twoZea mays L. Cultivars during rehydration

Growth behaviour, proline changes and water saturation deficit (WSD) changes were studied in two maize cultivars, Agati-76, a drought resistant oultivar, and cv. Vijay, a susceptible one after stress conditions were removed. Plants of both the cultivars showed a tendency to recover during rehydration. Phenotypically the plants appeared just normal on 7th day of rehydration, although recovery was never complete. Significant positive correlation existed between free proline content and concomitant change in water saturation deficit. Significantly higher proline content in cv. Agati-76 was reoorded in cv. Vijay, immediately after the stress was released, thereafter continuous decline was observed up to 7th day of rehydration in both the cultivars. Proline changes in relation to recovery of plants from stress conditions are discussed.     

Combined drought and heat stress in wheat: changes in some heat shock proteins

The influence of combined and individually applied drought and heat stress was studied in two wheat (Triticum aestivum L.) cultivars: resistant cv. Katya and susceptible cv. Sadovo. Relative water content decreased and electrolyte leakage increased due to individual and combined application of both stresses. Initial heat shock protein profile has been outlined via SDS electrophoresis of leaf extracts. The results obtained were confirmed by immunoblotting with anti-HSP70 monoclonal antibodies, anti-HSP110 polyclonal antibodies and anti-α β-crystalline polyclonal antibodies. The effect of simultaneously applied water stress and heat shock resembled the alterations in protein expression provoked only by water stress and differed significantly from the changes occurring after the individual application of heat stress.     

Effect of water stress on protein content in two maize cultivars differing in drought resistance

The changing pattern, of WSD and concomitant protein changes were scanned in twoZea mays cultivars, with differential sensitivity to water stress. Increasing protein values were recorded in resistant cv. Ageti-76 with decreasing osmotic potentials of substrate (on 3rd day of stress), although the values in susceptible cv. Vijay remained almost on a par with the controls. In another experiment both the cultivars revealed initial increase of protein on 2nd day at osmotic potentials of - 2 and -4 × 10⁶ Pa, however, values declined up to day 7 of stress. WSD showed an increasing trend in both the experiments, although slightly higher values of WSD were registered in cv. Ageti-76 in comparison with cv. Vijay. The significance of protein changes in reference to drought is discussed.     

Biochemical Changes in Excised Leaves of Oryza sativa Subjected to Water Stress

Excised rice (Oryza sativa L. cv. Ratna) leaves were used to compare the changes in the levels of various biochemical intermediates and enzyme activities during senescence in turgid and water-stressed conditions. Chlorophyll, total protein and soluble protein content decreased but α-amino nitrogen content increased during the senescence of turgid leaves. In the leaves subjected to water stress, these changes were accelerated, the acceleration being greater with higher degree of water stress. Starch, soluble sugars, total carbohydrates and non-reducing sugar content decreased during senescence of turgid leaves. Water stress accelerated the changes in the levels of starch and non-reducing sugar, but the changes in the levels of soluble sugars and total carbohydrates were retarded. Reducing sugar content increased at first and then decreased in the turgid leaves, and water stress accelerated the change. The decline in the catalase activity and the increase in the peroxidase activity with time was faster in the water-stressed leaves than in the turgid leaves. Acid inorganic pyrophosphatase activity increased, but alkaline inorganic pyrophosphatase activity decreased during the senescence of turgid leaves, and such changes were accelerated by water stress. The results suggest that water stress does not accelerate all the processes connected with leaf senescence.     

干旱胁迫下红砂幼苗非结构性碳水化合物动态变化特征

该试验以荒漠区主要建群种红砂幼苗为研究对象,设置适宜水分(CK)、轻度干旱(MD)、中度干旱(SD)和重度干旱(VSD)4个胁迫处理(即田间持水量的80%、60%、40%和20%),采用盆栽控水试验,分别测定干旱胁迫15、30、45和60 d时红砂幼苗的叶、茎、粗根和细根中非结构碳水化合物(NSC)及其组分的含量,分析不同胁迫强度下不同干旱持续时间红砂幼苗NSC的动态变化及各组分差异,以揭示红砂NSC对干旱胁迫的响应机制。结果表明:(1)干旱胁迫强度和胁迫持续时间对红砂幼苗不同器官NSC及其组分均有显著影响,其中胁迫持续时间对NSC动态变化的影响尤为显著。(2)干旱胁迫初期,红砂叶中的NSC含量呈下降趋势,而茎中的NSC含量呈上升趋势,粗根和细根中NSC含量在各胁迫处理下基本保持稳定。(3)干旱胁迫后期,红砂叶和茎中的可溶性糖、淀粉和NSC含量逐渐增加,而粗根和细根中的淀粉和NSC含量呈下降趋势(中度干旱除外),且这一时期重度干旱处理下各器官可溶性糖和NSC的含量明显高于CK。研究发现,重度干旱胁迫能显著诱导提高红砂幼苗不同器官中的NSC含量,并通过分解根中淀粉和增加叶片中可溶性糖含量的方式来调节细胞渗透势平衡,以维持细胞活力,进而保持红砂在干旱胁迫后期的存活。     

Comparison of the physiological responses of Phaseolus vulgaris and Vigna unguiculata cultivars when submitted to drought conditions

Three cultivars differing in their susceptibility to water stress were compared—Phaseolus vulgaris cv. Carioca (susceptible), Vigna unguiculata cv. IT83D (intermediately tolerant) and V. unguiculata cv. EPACE-1 (tolerant)—during an imposed water stress treatment. Variation in leaf gas exchange (i.e. assimilation and stomatal conductance) and leaf relative water content in response to progressive substrate water depletion were investigated. To verify the extent of the injury caused by the drought treatment, leaf gas exchange was measured after rehydration. In the three cultivars, stomatal conductance declined before leaf relative water content was affected. P. vulgaris showed the largest decrease in the rate of stomatal conductance with decreasing substrate water content compared to both V. unguiculata cultivars. Photosynthetic assimilation rates were largely dependent on stomatal aperture, but there was evidence of the participation of non-stomatal factors in the reduction of CO₂ fixation. The response of leaf gas exchange parameters to severe water stress conditions differed significantly between P. vulgaris and V. unguiculata cultivars. After rehydration, cultivars can be characterised according to the degree of injury induced by the drought treatment: V. unguiculata cv. EPACE-1 as the least affected, V. unguiculata cv. IT83D slightly affected and P. vulgaris cv. Carioca strongly affected. Similar ranking was obtained with experiments previously performed at a cellular and subcellular level. Our results confirm the utility of physiological parameters as early screening tools for drought resistance in bean cultivars.     

Photosynthetic CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>O gas exchange and dynamics of carbohydrates content in maize leaves under drought

We studied the temporal sequence of changes in the photosynthetic CO₂/H₂O gas exchange intensity, as well as leaf water status, contents of soluble carbohydrates, starch, proline, pigments, and MDA, in maize seedlings (Zea mays L., cv. Luchistaya) under adaptation to increasing water deficit. The duration of drought was 2, 3, 5, and 6 days. Withholding water from maize plants caused gradual increase in the intensity of water deficit: from mild (2 or 3 days) to moderate (5 days) and nearly severe (6 days) water stress. After 6 days, relative leaf water content decreased by 19.8% as compared to the control. On the second day after the onset of drought, slight reduction in the photosynthetic CO₂/H₂O gas exchange intensity of the treated plants was observed. After 6 days, photosynthesis and transpiration of leaves synchronously reduced almost threefold due to stomatal closure. The progressive soil drought had substantial impact on the carbohydrate metabolism. After 2 days of water deficit, the content of reducing sugars and sucrose increased slightly, whereas after 6 days, it increased ten and four times, respectively. After 2, 3, and 5 days of drought, the starch content declined slightly; however, under severe drought (6 days), it increased by 30% as compared to the control. Simultaneously with the increase in the content of soluble sugars, proline content increased significantly and it was the highest on the sixth day of drought. At all stages of water deficit, the proline content increased more significantly than the content of reducing carbohydrates and sucrose. Under increasing water deficit (5 and 6 days), the content of MDA was found to rise. At the initial drought stage (2 or 3 days) and under severe water deficit (6 days), no significant changes in the pigment content were observed. Thus, at the initial stages of progressive drought, in the leaves of this maize cultivar, a decline in photosynthetic activity proceeded simultaneously with accumulation of reducing sugars, sucrose, and proline. The results obtained showed that, at the first stages of adaptation of maize seedlings to drought, the changes in carbohydrate and proline metabolism have been observed, which have increased upon further plant dehydration.     

蒙古莸幼苗干旱致死过程中非结构性碳水化合物的变化

以一年生蒙古莸幼苗为对象,设置适宜水分、慢速干旱致死和快速干旱致死3个处理,研究不同干旱强度致死下蒙古莸幼苗各器官中非结构性碳水化合物(NSC,包括可溶性糖和淀粉)的含量变化及其分配规律.结果表明:慢速干旱致死胁迫下各器官可溶性糖含量与适宜水分组无显著差异.随时间的推移,茎可溶性糖含量先增加后减少,淀粉和NSC含量增加;粗根可溶性糖含量减少,淀粉和NSC含量增加;叶可溶性糖含量增加,淀粉和NSC含量减少.致死时(80 d),叶、茎、粗根和细根的NSC含量分别为6.2%、7.8%、8.3%和7.4%.快速干旱致死胁迫下,各器官可溶性糖含量均高于适宜水分处理组,而淀粉和NSC含量均低于适宜水分组.随时间的推移,根可溶性糖含量下降,淀粉和NSC含量上升;茎可溶性糖、淀粉和NSC含量均上升;叶可溶性糖含量上升,淀粉和NSC含量下降.致死时(30 d),叶、茎、粗根和细根的NSC含量分别为5.9%、6.6%、8.9%和7.7%.应对不同的干旱致死情况,蒙古莸幼苗各器官间非结构性碳水化合物呈现出不同的动态变化.在慢速干旱致死胁迫下,NSC优先为维持各器官生理代谢活动提供能量;而在快速干旱致死下,NSC主要以可溶性糖形式维持植物代谢,调节渗透势,促进吸水,应对急剧的干旱胁迫.     

干旱胁迫下新疆杨树冠不同高度叶片水分状况与非结构性碳动态北大核心CSCD

水力结构调整及非结构性碳动态对于认知干旱胁迫下植物生存前景和死亡风险至关重要。该研究以新疆杨(Populus bolleana Lauche.)为对象,通过干旱处理分析树冠不同高度叶片水力性状、光合生理特性、不同功能器官间的可溶性糖、淀粉及非结构性碳水化合物(NSC)含量变化,以甄别树冠不同高度叶片对干旱胁迫的生理响应和适应差异。结果表明:(1)在干旱胁迫下,树冠上部的叶水势、叶含水量、枝条含水量普遍低于下部,饱和膨压渗透势及膨压损失点水势在不同树冠高度间差异不显著;(2)干旱处理组植株净光合速率随树冠高度的增加而降低,叶绿素SPAD值在树冠的上部显著低于下部,而水分利用效率在树冠的上部却高于下部;(3)干旱处理组比叶面积在各树冠高度下显著低于对照组,而胡伯尔值在中部及上部高于对照组但差异不显著;(4)干旱处理组,树冠上部叶片淀粉含量显著高于下部,枝条可溶性糖及NSC含量在树冠上部显著高于下部,韧皮部的可溶性糖、淀粉及NSC含量在不同树冠高度间无显著差异,细根的可溶性糖、淀粉及NSC含量在对照组与干旱处理组间的差异不显著。研究发现,干旱处理下,树冠高度的增加会加剧新疆杨枝叶的干旱胁迫,致使树冠上部枝条木质部发生栓塞的风险大于下部,并导致NSC在不同器官间的分配和组分产生差异,但新疆杨植株可通过水分利用效率和形态上的适应性调整减缓干旱胁迫。     

苗期玉米叶片碳氮平衡与干旱诱导的叶片衰老之关系

为了探究干旱诱导的碳氮平衡破坏与干旱诱导的叶片衰老之间的关系,该实验以8个在干旱胁迫下叶片衰老进程有明显差异的玉米品种为实验材料,采用PEG模拟干旱处理,通过测定光合速率、叶绿素含量和叶绿素荧光参数等叶片衰老指标以及非结构性碳水化合物(可溶性糖、淀粉)和全氮含量等变化,分析玉米中干旱诱导的叶片衰老与叶片中碳氮平衡(碳氮比)之间的关系。结果显示:(1)干旱胁迫下,8个玉米品种叶片净光合速率受到严重抑制,Fv/Fm大幅下降,叶绿素含量显著降低,说明干旱诱导了玉米叶片的衰老;(2)干旱诱导玉米叶片衰老的同时,8个玉米品种的叶片中可溶性糖含量显著升高,淀粉含量小幅上升,全氮含量大幅降低,碳氮比显著升高,碳氮平衡遭到了破坏;(3)8个玉米品种叶片的叶绿素含量与非结构性碳水化合物含量以及碳氮比呈极显著负相关关系,与全氮含量呈极显著正相关关系。因此,碳氮代谢与干旱诱导的叶片衰老紧密联系,碳氮平衡可能参与了干旱诱导的叶片衰老调控。     

Comparison of Hexaploid and Tetraploid Wheat Cultivars in their Responses to Water Stress

We studied the effect of water stress imposed at anthesis and pre-anthesis stages on oxidative stress and antioxidant activity in four wheat cultivars, two hexaploid Triticum aestivum cultivars, drought resistant cv. C 306 and drought susceptible cv. Hira, and two tetraploid cultivars, T. durum cv. A 9-30-1 and T. dicoccum cv. HW 24. Water stress decreased relative water content (RWC), membrane stability index (MSI), and increased H₂O₂ and malondialdehyde (MDA) contents as well as activity of superoxide dismutase (SOD), catalase (Cat) and peroxidase (POX) in all the genotypes at all the stages. Both the tetraploid cultivars showed higher RWC, MSI and SOD activity, and lower H₂O₂ and MDA contents under water stress than hexaploid ones. Cat and POX activities were highest in C 306.     

Physiological and anatomical changes induced by drought in two olive cultivars (cv Zalmati and Chemlali)

Photosynthetic gas exchange, vegetative growth, water relations and fluorescence parameters as well as leaf anatomical characteristics were investigated on young plants of two Olea europaea L. cultivars (Chemlali and Zalmati), submitted to contrasting water availability regimes. Two-year-old olive trees, grown in pots in greenhouse, were not watered for 2 months. Relative growth rate (RGR), leaf water potential (Ψ_LW) and the leaf relative water content (LWC) of the two cultivars decreased with increasing water stress. Zalmati showed higher values of RGR and LWC and lower decreased values of Ψ_LW than Chemlali, in response to water deficit, particularly during severe drought stress. Water stress also caused a marked decline on photosynthetic capacity and chlorophyll fluorescence. The net photosynthetic rate, stomatal conductance, transpiration rate, the maximal photochemical efficiency of PSII (F _v/F _m) and the intrinsic efficiency of open PSII reaction centres (F′ _v/F′ _m) decreased as drought stress developed. In addition, drought conditions, reduced leaf chlorophyll and carotenoids contents especially at severe water stress. However, Zalmati plants were the less affected when compared with Chemlali. In both cultivars, stomatal control was the major factor affecting photosynthesis under moderate drought stress. At severe drought-stress levels, the non-stomatal component of photosynthesis is inhibited and inactivation of the photosystem II occurs. Leaf anatomical parameters show that drought stress resulted in an increase of the upper epidermis and palisade mesophyll thickness as well as an increase of the stomata and trichomes density. These changes were more characteristic in cv. ‘Zalmati’. Zalmati leaves also revealed lower specific leaf area and had higher density of foliar tissue. From the behaviour of Zalmati plants, with a smaller reduction in relative growth rate, net assimilation rate and chlorophyll fluorescence parameters, and with a thicker palisade parenchyma, and a higher stomatal and trichome density, we consider this cultivar more drought-tolerant than cv. Chemlali and therefore, very promising for cultivation in arid areas.     

Flower abscission and inflorescence carbohydrates in sensitive and non-sensitive cultivars of grapevine

The Gewurztraminer (GW) and the Pinot noir (PN) cultivars of grapevine differ in their sensitivity to environmental factors that can cause flower abscission, cv. GW being the most sensitive. In order to further define the mechanisms leading to abscission, and owing to the importance of sugars in the achievement of sexual organ ontogenesis, we attempted to correlate the chronology of flower ontogenesis with the variations of carbohydrates in the inflorescence. In the vineyard, under optimal climatic conditions, fruit set of cv. GW and cv. PN was 82% and 65%, respectively. The sugar distribution was different in their inflorescences during the entire duration of flower development. Between stages 15 and 17, flowers of GW and PN reached the crucial meiosis stage. At that time, the inflorescences of cv. GW exhibited higher concentrations of starch and sucrose, whereas those of PN presented higher levels of glucose and fructose. Despite higher starch concentrations in GW inflorescences, starch reserves were present in the ovules and anthers of PN but not in those of GW. These results suggest that the higher content of reserve and transport carbohydrates in the inflorescences of GW favour flower development and fruit set under optimal environmental conditions. Furthermore, since meiosis represents a key step of female development, the different sugar concentrations in the inflorescences of the two cultivars at stages 15 and 17 could be related to the sensitivity to flower abscission under climatic stress. In particular, the presence of starch granules in PN ovules and anthers might explain the higher resistance of this cultivar to flower abscission.     

Effect of drought on chlorophyll content and antioxidant enzyme activities in leaves of three wheat cultivars varying in productivity

Seedlings of three wheat varieties (Triticum aestivum L.)—highly productive cv. Ballada, moderately productive cv. Belchanka, and low productive cv. Beltskaya—were exposed to progressive soil drought (cessation of watering for 3, 5, and 7 days) and then analyzed for chlorophyll content and activities of ferredoxin-NADP⁺ oxidoreductase (FNR) and antioxidant enzymes, namely, glutathione reductase (GR) and ascorbate peroxidase (AscP). In addition, the proline content, and the extent of lipid peroxidation were examined. In the first period of water limitation, the water loss from leaves was slight for all wheat cultivars, which is characteristic of drought-resistant varieties. After 7-day drought the leaf water content decreased by 5.2–6.8%. The total chlorophyll content expressed per unit dry weight increased insignificantly during the first two periods of drought but decreased by 13–15% later on. This decrease was not accompanied by changes in chlorophyll a/b ratio. The plant dehydration did not induce significant changes in FNR activity. Activities of GR and AscP in leaves of wheat cultivars Ballada and Belchanka increased on the 3rd and 5th days of drought. Owing to the coordinated increase in GR and AscP activities, the lipid peroxidation rate remained at nearly the control level observed in water-sufficient plants. When the dehydration period was prolonged to 7 days, activities of GR and AscP in wheat cultivars reduced in parallel with the increase in malonic dialdehyde (MDA) content, indicating that the antioxidant enzyme defense system was weakened and lipid peroxidation enhanced. Unlike Ballada and Belchanka, the wheat cv. Beltskaya did not exhibit the increase in GR and AscP activities during progressive soil drought. The increase in MDA content by 16% in this cultivar was only observed after a 7-day drought period. The proline content in leaves of all wheat cultivars increased substantially during drought treatment. Thus, in wheat cultivars examined, different responses of the defense systems were mobilized to implement plant protection against water stress. The activities of antioxidant enzyme defense system depended on wheat cultivar, duration of drought, and the stage of leaf development.     

甘草叶片渗透调节物质及蔗糖代谢相关酶对干旱胁迫的响应特性

该研究以甘草幼苗为试材,采用盆栽自然干旱方法,设计对照(CK)、轻度(LS)、中度(MS)、重度(SS)干旱胁迫处理,测定分析甘草叶片的渗透调节物质及蔗糖代谢相关酶[蔗糖磷酸合成酶(SPS)、蔗糖合成酶合成方向(Ss+)、蔗糖合成酶分解方向(Ss-)、中性转化酶(NI)、酸性转化酶(AI)、淀粉磷酸化酶(SP)]活性的变化,以探讨甘草的渗透调节特性以及糖分调节的酶学机制,揭示甘草对干旱胁迫的响应机理。结果显示:(1)随着干旱胁迫程度的加剧,甘草叶片可溶性糖、可溶性蛋白和脯氨酸含量呈逐渐增加的趋势,束缚水/自由水的比值呈先增加后降低的趋势。(2)随着干旱胁迫程度的加剧,甘草叶片蔗糖、葡萄糖、果糖含量均呈先升高后降低的趋势,但不同胁迫强度出现峰值的时间不同;其中在CK和LS干旱胁迫时蔗糖含量淀粉含量葡萄糖含量果糖含量,在MS和SS干旱胁迫时淀粉含量葡萄糖含量蔗糖含量果糖含量,表明随着干旱程度的增加,甘草叶片中蔗糖转化成了淀粉。(3)随着干旱胁迫程度的加重,甘草叶片的SPS活性呈先升高后降低的趋势,Ss活性和Inv(蔗糖转化酶)活性呈逐渐升高的趋势,SP活性呈逐渐降低的趋势;各胁迫处理的Ss+活性与CK差异不显著,而Ss-活性与CK差异显著,并且Ss-活性在各胁迫处理下远大于Ss+活性,表明甘草叶片Ss-活性在蔗糖代谢过程中占主导作用。(4)相关分析结果显示,在LS中,NI与蔗糖呈负相关关系,Ss-与淀粉呈显著正相关关系、与蔗糖呈负相关关系;在MS中,蔗糖和葡萄糖与SPS、Ss+、Ss-、NI和AI均呈正相关关系,与SP呈负相关关系;在SS中,SP和NI与蔗糖呈正相关关系,而与淀粉呈负相关关系;表明在轻度干旱处理下,Ss参加了蔗糖的分解,继而合成淀粉;在中度和重度干旱条件下,SP主要催化淀粉的分解来增加蔗糖含量以此平衡蔗糖代谢。     

五唇兰对PEG模拟的干旱胁迫响应研究

为了解干旱对五唇兰(Phalaenopsis pulcherrima)生长的影响,以聚乙二醇(PEG)溶液模拟干旱胁迫,对其叶片的光合色素、渗透调节物质和非结构碳水化合物(NSC)含量变化进行研究。结果表明,随着PEG浓度增加,五唇兰植株含水量和鲜质量逐渐下降,以PEG为13.75%～14.84%时最显著。PEG处理显著降低叶片的叶绿素a和b含量。随着植株含水量的降低,叶片可溶性蛋白、淀粉(St)含量均呈下降趋势,可溶性糖(SS)含量、NSC和SS/St均呈先升后降的趋势。因此,干旱胁迫会影响五唇兰植株的含水量和光合产物的积累;在较低程度干旱胁迫下,可溶性糖在抗旱响应中发挥主要作用;随着干旱胁迫程度加深,五唇兰的生理代谢受到严重影响。     

Changes in Mulberry Leaf Metabolism in Response to Water Stress

A series of experiments were conducted to characterize the water stress-induced changes in the activities of RuBP carboxylase (RuBPCO) and sucrose phosphate synthase (SPS), photosystem 2 activity, and contents of chlorophylls, carotenoids, starch, sucrose, amino acids, free proline, proteins and nucleic acids in mulberry (Morus alba L. cv. K-2) leaves. Water stress progressively reduced the activities of RuBPCO and SPS in the leaf extracts, the chlorophyll content, and PS2 activity in isolated chloroplasts. Plants exposed to drought showed lower content of starch and sucrose but higher total sugar content than control plants. While the soluble protein content decreased under water stress, the amino acid content increased. Proline accumulation (2.5-fold) was noticed in stressed leaves. A reduction in the contents of DNA and RNA was observed. Reduced nitrogen content was associated with the reduction in nitrate reductase activity. SDS-PAGE protein profile showed few additional proteins (78 and 92 kDa) in the water stressed plants compared to control plants.     

Response of antioxidant and osmoprotective systems of wheat seedlings to drought and rehydration

Complex study of the effect of soil drought (72 h) and subsequent rehydration for 24 and 48 h on the activities of antioxidant and osmoprotective systems in the leaves of young plants of winter wheat (Triticum aestivum L.) cvs. Ballada (high productivity) and Beltskaya (low productivity) was carried out. Under drought conditions, the content of water in the leaves of cv. Ballada reduced to a lesser degree than in the leaves of cv. Beltskaya. Drought did not affect the rate of leaf growth in cv. Ballada but retarded leaf growth in cv. Beltskaya. Under drought conditions, the content of ascorbate reduced in cv. Beltskaya but was not changed in cv. Ballada; the content of glutathione increased by 19% in cv. Ballada and by 30% in cv. Beltskaya. Under drought conditions, ascorbate peroxidase activity was not changed in cv. Ballada whereas in cv. Beltskaya there was a tendency to its decrease. Glutathione reductase activity in the leaves of cv. Beltskaya increased stronger than in cv. Ballada. Substantial differences between cultivars in the accumulation of reducing sugars and sucrose under water deficit were observed. In both cultivars, drought induced an active proline accumulation. Observed differences in the cultivar responses to water stress evidently indicate differences in the strategy of their adaptation to drought. Drought did not affect the contents of chlorophyll and MDA in both cultivars. The data obtained allow a suggestion that, under conditions of moderate soil drought, the coordinated system of antioxidant defense and osmotic control functioned sufficiently effective; as a result, oxidative stress was not developed in both cultivars. Young plants of both cultivars differing in their responses to water deficit retained the ability to recover after rehydration.     

Biochemical Changes in Leaf Tissues of Taro [Colocasia esculenta L. (Schott)] Infected with Phytophthora colocasiae

The changes in some biochemical parameters due to Phytophthora leaf blight infection were assessed in leaf tissues of one resistant (DP‐25), two moderately resistant (Duradim and Jhankri) and one susceptible (N‐118) genotypes of taro [Colocasia esculenta (L.) Schott]. Phytophthora spore suspension (15 000 spore/ml water) was sprayed onto the in vitro raised taro plantlets at 30 days after establishment in pots to induce disease. In comparison with the uninoculated leaves, blight infected leaves showed reduction in protein content and activity of nitrate reductase and increase in total soluble sugar, reducing sugar content and activities of acid phosphatase and alkaline phosphatase among the studied genotypes. Changes in biochemical parameters under induced blight stress as compared with uninoculated control were less in resistant genotypes than that in susceptible genotype. The deviations in biochemical contents were highest in susceptible genotype N‐118. Based on the variations of above parameters under stress and non‐stress control among the four tested genotypes, the overall pattern of changes was N‐118 > Duradim > Jhankri > DP‐25, which is in accordance with the pattern of increasing resistance. The resistant genotypes could be used for commercial cultivation and genetic improvement programme to develop resistant varieties to Phytophthora leaf blight disease.     

Some Physiological Characteristics in Resistant and Susceptible Cotton Cultivars Infected with Cotton Leaf Curl Virus

Eight cultivars/lines of Gossypium hirsutum (CIM-443, CIM-448, CIM-1100, FH-634, S-111, S-113, Cedix, and LRA 5166) resistant to cotton leaf curl virus (CLCuV), one moderately-resistant (cv. NIAB-Krishma), and one susceptible (cv. S-12) were used. All the resistant lines remained free of all disease symptoms, whereas in moderately-resistant and susceptible cvs. leaf curling and vein thickening occurred. Cultivars with varying degree of CLCuV-resistance had different pattern of accumulation of macronutrients. Leaf N content was lowest in S-12, but increased considerably due to disease. Leaf K and Ca contents of S-12 were lower in the diseased leaves than in healthy ones. Chlorophyll a and b contents were highest in lines S-111, S-113 and S-12. A marked reduction in chlorophyll b content was observed in the diseased leaves of S-12. Leaf water potential in S-12 and NIAB-Krishma was also decreased due to disease. The most distinctive characteristic to differentiate between lines was epicuticular wax content, since all the resistant lines had considerably higher wax content on their leaf surfaces than the moderately-resistant or susceptible cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.