辣椒开花结果期对干旱胁迫的形态与生理响应

在遮雨网室选用抗旱性较强的农城椒二号和抗旱性较弱的陕蔬2001,研究辣椒在轻度、中度和重度干旱胁迫下不同时间的生长、产量、渗透调节物质、保护酶活性的变化规律及其生理调节机制。结果表明:随干旱胁迫时间的延长,辣椒的株高、分枝数、叶面积、单位面积产量、叶绿素含量和叶片相对含水量的抗旱系数呈下降趋势,下降速率与干旱胁迫程度呈正相关,与品种的抗旱性呈负相关;脯氨酸、丙二醛含量和细胞膜透性相对值随干旱胁迫时间的延长呈上升趋势;POD、SOD、CAT活性和可溶性蛋白相对值随着干旱胁迫时间的延长先升高后下降,抗旱性强的材料增加幅度低于抗旱性弱的材料;可溶性糖含量的相对值在轻度和中度干旱胁迫下呈上升趋势,在重度干旱胁迫下呈上升—下降趋势,且抗旱性强的材料上升速度大于抗旱性弱的材料。相关分析表明,干旱胁迫下,产量与株高、分枝数、叶片叶绿素含量、叶面积、叶片相对含水量抗旱系数呈显著正相关;与细胞膜透性、CAT活性和可溶性蛋白含量抗旱系数呈显著负相关。主成分分析表明,用作辣椒抗旱性鉴定的主要指标是单株产量、株高、叶面积、分枝数、可溶性蛋白、可溶性糖、MDA、叶绿素含量和细胞膜透性及叶片相对含水量,叶片POD、SOD、CAT活性、脯氨酸含量可做为辣椒抗旱性鉴定的次要鉴选指标。     

2个欧李品种对碳酸盐胁迫生理响应的初步研究

在盆栽条件下,以不同浓度的NaHCO₃溶液浇灌农大欧李3和4号2年生组培苗,测定苗木叶片的生理指标。结果表明：随胁迫时间的延长,两个品种的叶绿素a呈先变化平缓后降低趋势,各处理间差异显著;叶绿素a/b在整个处理时期变化平稳;脯氨酸呈先变化平缓后升高趋势;农大欧李3号的电解质外渗率、MDA和POD活性呈先变化平缓后升高再降低的趋势,各处理间差异不显著;中、低浓度SOD活性整个胁迫期变化平缓,高浓度的在整个胁迫期间变化较大,各处理间差异极其显著;农大欧李4号电解质外渗率、SOD、POD和MDA在处理期间呈先升高后降低趋势,胁迫解除后,高浓度处理的电解质外渗率、SOD、POD活性上升、低浓度处理下降,MDA则相反。在长期的NaHCO₃胁迫过程中,农大欧李3号和4号都显示了强的耐盐性。     

PEG模拟干旱胁迫对糜子幼苗生理特性的影响

以'榆糜1号'和'榆糜3号'为试验材料,采用PEG模拟水分胁迫方法,研究了干旱胁迫对糜子幼苗生理生化特性的影响.结果显示,(1)2品种幼苗叶片的细胞电解质外渗率、叶片的MDA含量、游离脯氨酸含量和可溶性糖含量均在胁迫2 d后逐渐上升,但保护酶SOD和POD的活性均呈先升高后降低的变化趋势,2品种幼苗在不同强度PEG胁迫下总体变化趋势基本一致,且各胁迫处理间差异显著(P<0.05).(2)2品种在相同处理下差异显著(P<0.05),其中,10%～30 0A PEG胁迫8 d时,'榆糜3号'比'榆糜1号'的细胞电解质外渗率、叶片的MDA含量增加幅度小,而游离脯氨酸含量和可溶性糖含量增加幅度较大,但保护酶SOD和POD的活性下降幅度较小,说明相同渗透胁迫下'榆糜1号'比'榆糜3号'叶片的细胞膜透性增加幅度大,但渗透调节物质增加较少,细胞膜系统受干旱伤害会更大,其抗旱性相对较弱.综合各项生理指标的分析认为,'榆糜3号'具有较强的抗旱能力.     

二倍体和四倍体杂交兰幼苗对低温胁迫的生理响应差异分析

为探究不同倍性杂交兰（Cymbidium hybrid）对低温胁迫的生理响应差异,对低温胁迫下（昼温10℃、夜温4℃）二倍体杂交兰以及四倍体杂交兰株系T1和T2幼苗叶片中脯氨酸、可溶性糖、可溶性蛋白质、MDA和叶绿素含量,O-·2产生速率以及SOD、POD和CAT活性的动态变化进行了测定和分析;在此基础上,比较了二倍体和四倍体杂交兰的耐低温特性差异。结果显示：随着胁迫时间的延长,二倍体杂交兰和四倍体杂交兰株系T1和T2幼苗叶片中脯氨酸、可溶性糖、可溶性蛋白质和MDA含量,O-·2产生速率以及POD和CAT活性总体呈逐渐增加的趋势;叶绿素含量呈逐渐下降的趋势;SOD活性呈先上升后下降的趋势,并分别在胁迫后第9天和第6天达到峰值。在常温（25℃）下恢复生长3d后,二倍体杂交兰和四倍体杂交兰株系T1和T2幼苗叶片中脯氨酸、可溶性糖、可溶性蛋白质和MDA含量,O-·2产生速率以及SOD、POD和CAT活性均降低,而叶绿素含量升高。总体上,二倍体杂交兰叶片中脯氨酸、可溶性糖和可溶性蛋白质含量以及SOD、POD和CAT活性的增幅明显小于四倍体杂交兰,MDA含量和O-·2产生速率的增幅则大于四倍体杂交兰,而叶绿素含量的降幅则明显大于四倍体杂交兰。综合分析结果表明：在低温胁迫下,四倍体杂交兰叶片中渗透调节物质含量和保护酶活性均较高,其对低温的耐性强于二倍体杂交兰。     

Na2CO3胁迫对芦荟幼苗叶片叶绿体保护酶和渗透调节物质的影响

以盆栽耐盐碱芦荟'不夜城'幼苗为材料,采用不同浓度Na2CO3溶液(不同渗透势)处理芦荟幼苗7 d后,测定其叶片叶绿体保护酶超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸氧化酶(APX)、谷胱甘肽转移酶(GST)活性以及叶绿素、丙二醛(MDA)、渗透调节物质含量和电解质外渗率等的变化,以探讨芦荟抵抗盐碱胁迫伤害的机制.结果显示:当溶液渗透势较高时(大于-7.19×105 Pa),Na2CO3胁迫下的芦荟幼苗叶片叶绿体保护酶活性都呈显著上升趋势,而叶绿素含量、可溶性蛋白、MDA含量以及电解质外渗率却无明显变化;在溶液渗透势较低时(小于-7.19×105 Pa),Na2CO3胁迫下芦荟幼苗的渗透调节物质含量显著增高,叶绿体保护酶活性特别是叶绿素含量显著下降,而MDA含量和电解质外渗率却呈上升的趋势.研究表明:一定浓度的Na2CO3胁迫下,芦荟幼苗可以通过提高自身叶绿体保护酶的活性来降低活性氧的积累量,同时提高渗透调节能力来增强其抗逆性;但在过高浓度的盐碱胁迫下,过高的Na+浓度和pH也会对芦荟幼苗叶片造成一定的氧化伤害.     

干旱胁迫对烟草两品种幼苗生理生化特性及NtDEGP5基因表达的影响

以烟草Nicotianatabacum抗旱品种NC82和干旱敏感品种云烟87幼苗为材料,利用PEG-6000对幼苗进行干旱胁迫处理,研究干旱胁迫对烟草不同品种Fv/Fm、SOD活性、POD活性、MDA含量等生理生化指标及NtDEGP5基因表达的影响,为进一步开展NtDEGP5基因的功能研究提供依据。结果表明,干旱胁迫对烟苗的Fv/Fm、SOD活性、POD活性、MDA含量有影响,随着干旱的持续,Fv/Fm呈逐渐下降趋势,POD、SOD活性和MDA含量呈先升高后降低的趋势;不同品种对干旱胁迫的响应有差异,在干旱胁迫0～9 h,云烟87幼苗的Fv/Fm降幅大于NC82,POD、SOD活性、MDA含量的增幅小于NC82,胁迫12h后与对照差异不显著。干旱胁迫下不同品种、不同器官间的Nt DEGP5基因表达有差异,云烟87幼苗根、茎、叶中的表达量均较低,NC82幼苗根中的表达量较低,但干旱胁迫9～12 h后叶和茎的表达量较高。NC82幼苗叶片NtDEGP5基因表达量与Fv/Fm、POD活性、MDA含量呈显著正相关。Fv/Fm、SOD活性、POD活性、MDA含量可作为烟草苗期抗旱性评价指标,NtD...     

蚜虫(Aphis medicaginis Koch)危害胁迫对不同苜蓿品种体内丙二醛含量及防御性酶活性的影响

研究了蚜虫危害胁迫后不同抗蚜性苜蓿品种叶片内丙二醛含量及防御性酶活性的动态变化。结果表明：在蚜虫刺吸诱导的过程中，高感品种的MDA含量始终高于高抗品种，并且高感和高抗品种均保持上升的趋势;高感品种的SOD、POD和PAL活性始终低于高抗品种，其中高感和高抗品种的SOD和POD活性均表现先上升后下降的趋势，而PAL活性上升到高峰后均趋于稳定;CAT活性在高感和高抗品种间表现为交替的上升下降;高抗品种的PPO活性前期低于高感品种，而后期高于高感品种。由此可见，在蚜虫危害胁迫下，高感和高抗品种间MDA、SOD、POD、PAL和PPO活性的变化与苜蓿的抗蚜性密切相关，均可作为苜蓿抗蚜性鉴定的生理指标，而CAT活性变化与苜蓿抗蚜性的联系有待进一步研究。     

氯化胆碱对盐胁迫黄瓜幼苗渗透调节物质及活性氧代谢系统的影响

以盐敏感型黄瓜品种津春4号为材料,采用水培方法研究了叶面喷施不同浓度(0.5、1.0和1.5 mmol·L-1)氯化胆碱(CC)对NaCl胁迫(75 mmol·L-1)下黄瓜幼苗鲜重、叶片叶绿素、渗透调节物质含量及活性氧代谢系统的影响.结果表明:(1)单独CC处理可提高黄瓜叶片的叶绿素、可溶性糖和可溶性蛋白含量以及过氧化氢酶(CAT)与过氧化物酶(POD)活性,降低O2·-产生速率,但对植株鲜重及超氧化物岐化酶(SOD)活性影响不大;(2)NaCl胁迫处理增加了黄瓜幼苗叶片中可溶性糖和可溶性蛋白含量,增强了SOD、POD和CAT活性,提高了O2·-产生速率及丙二醛(MDA)的含量,但同时降低了叶绿素含量与植株鲜重;(3)盐胁迫前CC预处理可缓解黄瓜幼苗叶绿素含量和植株鲜重的下降、以及MDA含量和O2·-产生速率的上升趋势,且进一步提高了盐胁迫下黄瓜叶片中SOD、POD和CAT活性.因此,适宜浓度的氯化胆碱可显著提高盐胁迫下黄瓜叶片的抗氧化酶活性,提高清除活性氧的能力,缓解盐胁迫对黄瓜幼苗细胞膜的伤害,增强黄瓜幼苗的耐盐性.     

硒对镉胁迫下水稻幼苗生长及生理特性的影响

采用溶液培养 ,研究不同浓度的硒和镉处理对稻苗的株高、叶片干重、叶绿素、还原糖、叶片丙二醛含量以及保护酶 SOD、POD、CAT活性的影响。结果表明 ,镉胁迫下稻苗矮化 ,镉毒害使叶片失绿 ,干重降低 ,还原糖含量下降 ,叶片 MDA含量增加 ,POD活性增强 ,而 SOD、CAT活性降低 ;硒可减轻镉对水稻的毒害 ,表现为 :减轻镉胁迫对株高增加的抑制 ,提高叶绿素含量 ,增加叶片干物质积累 ,提高叶片还原糖含量 (Cd0 .5 mg/ L加 Se 0 .1 0～ 0 .5 0 mg/ L例外 ) ,降低 MDA含量与 POD活性 ,提高 SOD、CAT活性     

栓皮栎幼苗对土壤干旱胁迫的生理响应

以栓皮栎一年生盆栽苗为实验材料,采用称重控水的方法,设置不同土壤水分胁迫梯度,系统分析其幼苗在不同干旱胁迫条件下的生理生化响应特征,以探索栓皮栎耐旱特性.结果显示:(1)栓皮栎幼苗叶片中3种保护酶(SOD、POD、CAT)活性在对照(CK,土壤相对含水量19.5％～21.5％)条件下保持稳定,而中度干旱(T2,9.5％～11.5％)和重度干旱(T3,5.5％～7.5％)条件下,随着胁迫时间的延长呈先增高后降低的趋势,且变化的幅度在不同胁迫强度下存在差异.(2)在整个干旱胁迫过程中,各胁迫处理叶片丙二醛(MDA)含量均呈上升趋势,不同胁迫强度的变化幅度不同;叶片中的可溶性蛋白含量和根系活力随着干旱胁迫程度的增强呈先增高后降低的趋势.(3)栓皮栎幼苗叶片的脯氨酸含量随着干旱胁迫时间的延长表现出先增加后降低的趋势;叶片叶绿素a、叶绿素b、总叶绿素含量以及叶绿素a/b值均呈逐渐降低的趋势.研究表明,栓皮栎幼苗在短期和轻度干旱胁迫下通过提高自身的保护酶活性、增加可溶性蛋白和脯氨酸含量、提高根系活力等来抵御干旱环境的伤害,从而表现出较强的耐旱特性;而在重度干旱胁迫条件下,栓皮栎幼苗自我调节能力丧失,体内代谢紊乱,导致保护酶活性、可溶性蛋白、脯氨酸含量和根系活力等下降,从而受到干旱伤害.     

NaCl胁迫对棉花种子萌发和幼苗生长的伤害

采用盐化土壤盆栽方法,选择耐盐性较强品种枝棉３号和耐盐性较弱品种泗棉２号,研究了盐分对棉花（Ｇｏｓｓｙｐｉｕｍ ｈｉｒｓｕｔｕｍ Ｌ．）种子萌发、出苗和幼苗生长的伤害。结果表明,在－０．５５和－１．１０ＭＰａ盐分胁迫下,对棉花伤害起决定性作用的因子是Ｎａ＾＋。２００ｍｍｏｌ／Ｌ ＮａＣｌ胁迫下,枝棉３号种子萌发时电导率上升幅度和子叶ＣＡＴ下降幅度均显著小于泗棉２号。１００和２００ｍｍｏｌ／Ｌ Ｎａ     

Effect of Water Stress on Photosynthesis in Two Mulberry Genotypes with Different drought Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (drought tolerant S13 and drought sensitive S54) were subjected to water stress for 15 d. Water stress decreased the leaf water potential, net photosynthetic rate (PN), and stomatal conductance (gs) in both the cultivars. However, the magnitude of decline was comparatively greater in the sensitive cultivar (S54). Intercellular CO2 concentration (Ci) was unaltered during mild stress, but significantly increased at severe stress in both cultivars. The photosystem 2 activity significantly declined only at a severe stress in both cultivars. The Ci/gs ratio representing the mesophyll efficiency was greater in the tolerant cultivar S13. Involvement of stomatal and/or non-stomatal components in declining PN depended on the severity and duration of stress. However, the degree of non-stomatal limitations was relatively less in the drought tolerant cultivar.     

Photosynthetic characteristics and enzymatic antioxidant capacity of leaves from wheat cultivars exposed to drought

Two durum (Triticum durum L.), Barakatli-95 and Garagylchyg-2; and two bread (Triticum aestivum L.) wheat cultivars, Azamatli-95 and Giymatli-2/17 with different sensitivities to drought were grown in the field on a wide area under normal irrigation and severe water deficit. Drought caused a more pronounced inhibition in photosynthetic parameters in the more sensitive cvs Garagylchyg-2 and Giymatli-2/17 compared with the tolerant cvs Barakatli-95 and Azamatli-95. Upon dehydration, a decline in total chlorophyll and relative water content was evident in all cultivars, especially in later periods of ontogenesis. Potential quantum yield of PS II (F(v)/F(m) ratio) in cv Azamatli-95 was maximal during stalk emergency stage at the beginning of drought. This parameter increased in cv Garagylchyg-2, while in tolerant cultivar Barakatli-95 significant changes were not observed. Contrary to other wheat genotypes in Giymatli-2/17 drought caused a decrease in PS II quantum yield. Drought-tolerant cultivars showed a significant increase in CAT activity as compared to control plants. In durum wheat cultivars maximal activity of CAT was observed at the milk ripeness and in bread wheat cultivars at the end of flowering. APX activity also increased in drought-treated leaves: in tolerant wheat genotypes maximal activity occurred at the end of flowering, in sensitive ones at the end of ear formation. GR activity increased in the tolerant cultivars under drought stress at all stages of ontogenesis. SOD activity significantly decreased in sensitive cultivars and remained at the control level or increased in resistant ones. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Influence of waterlogging on some anti-oxidative enzymatic activities of two barley genotypes differing in anoxia tolerance

The experiment was conducted to investigate the formation of oxidative stress and the development of anti-oxidative enzymes in two barley genotypes differing in anoxia tolerance. Waterlogging led to significant reduction in root and shoot weight, green leaf area and tillers per plant, but tolerant Xiumai 3 was much less reduced than sensitive Gerdner. Malondialdehyde (MDA) content, an indicator of membrane lipid peroxidation, significantly increased in Gerdner when the plants were subjected to waterlogging, but remained little changed in Xiumai 3. Superoxide dismutase (SOD) activity was increased with waterlogging treatment and the sensitive cultivar had higher activity than the tolerant one during the experimental duration. At early stage of waterlogging treatment, both peroxidase (POD) and catalase (CAT) activities significantly increased in Xuimai 3, while obviously decreased in Gerdner. Moreover, both cultivars showed substantial increase in both POD and CAT with the progress of waterlogging exposure. Glutathione reductase (GR) activity was increased in both tolerant- and sensitive cultivars under waterlogging. It may be assumed from the current results that SOD activity appears to be not a constraining factor limiting the scavenging of ROS, and it is the change of POD and CAT activity under waterlogging that determine the status of oxidative stress. The difference between genotypes in waterlogging tolerance could be distinguished from the changed patterns of these enzymatic activities.     

Differential responses of antioxidative system to chilling and drought in four rice cultivars differing in sensitivity

Responses of antioxidative defense systems to chilling and drought stresses were comparatively studied in four cultivars of rice (Oryza sativa L.) differing in sensitivity, two of them (Xiangnuo no. 1 and Zimanuo) are tolerant to chilling but sensitive to drought and the other two (Xiangzhongxian no. 2 and IR50) are tolerant to drought but sensitive to chilling. The seedlings of rice were transferred into growth chamber for 5 d at 8 degrees C as chilling treatment, or at 28 degrees C as control, or at 28 degrees C but cultured in 23% PEG-6000 solution as drought stress treatment. Under drought stress the elevated levels of electrolyte leakage, contents of H(2)O(2) and total thiobarbituric acid-reacting substances (TBARS) in Xiangzhongxian no. 2 and IR50 are lower than those in Xiangnuo no. 1 and Zimanuo. On the contrary, Xiangnuo no. 1 and Zimanuo have much lower level of electrolyte leakage, H(2)O(2) and TBARS than Xiangzhongxian no. 2 and IR50 under chilling stress. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase, and ascorbate-peroxidase (APX)) and contents of antioxidants (ascorbaic acid and reduced glutathione) were measured during the stress treatments. All of them were enhanced greatly until 3 d after drought stress in the two drought-tolerant cultivars, or after chilling stress in the two chilling-tolerant cultivars. They all were decreased at 5 d after stress treatments. On the other hand, activities of antioxidant enzymes and contents of antioxidants were decreased greatly in the drought-sensitive cultivars after drought stress, or in the chilling-sensitive cultivars after chilling stress. The results indicated that tolerance to drought or chilling in rice is well associated with the enhanced capacity of antioxidative system under drought or chilling condition, and that the sensitivity of rice to drought or chilling is linear correlated to the decreased capacity of antioxidative system.     

Expression profiling of rice cultivars differing in their tolerance to long-term drought stress

Understanding the molecular basis of plant performance under water-limiting conditions will help to breed crop plants with a lower water demand. We investigated the physiological and gene expression response of drought-tolerant (IR57311 and LC-93-4) and drought-sensitive (Nipponbare and Taipei 309) rice (Oryza sativa L.) cultivars to 18 days of drought stress in climate chamber experiments. Drought stressed plants grew significantly slower than the controls. Gene expression profiles were measured in leaf samples with the 20 K NSF oligonucleotide microarray. A linear model was fitted to the data to identify genes that were significantly regulated under drought stress. In all drought stressed cultivars, 245 genes were significantly repressed and 413 genes induced. Genes differing in their expression pattern under drought stress between tolerant and sensitive cultivars were identified by the genotype x environment (G x E) interaction term. More genes were significantly drought regulated in the sensitive than in the tolerant cultivars. Localizing all expressed genes on the rice genome map, we checked which genes with a significant G x E interaction co-localized with published quantitative trait loci regions for drought tolerance. These genes are more likely to be important for drought tolerance in an agricultural environment. To identify the metabolic processes with a significant G x E effect, we adapted the analysis software MapMan for rice. We found a drought stress induced shift toward senescence related degradation processes that was more pronounced in the sensitive than in the tolerant cultivars. In spite of higher growth rates and water use, more photosynthesis related genes were down-regulated in the tolerant than in the sensitive cultivars.     

The effect of salt stress on lipid peroxidation and antioxidants in the leaf of the cultivated tomato and its wild salt‐tolerant relative Lycopersicon pennellii

The possible involvement of the antioxidative system in the tolerance to salt stress was studied in the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (M82) and its wild salt‐tolerant relative L. pennellii (Corn) D'Arcy accession Atico (Lpa). All analyses, except that of monodehydroascorbate reductase (MDHAR), were performed of the youngest fully‐expanded leaf of control and salt (100 m M NaCl) stressed plants, 4, 7, 10, 14, 18 and 22 days after completing the stress treatment. In Lpa, constitutive level of lipid peroxidation and activities of catalase (CAT) and glutathione reductase (GR) were lower while the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were inherently higher than in M82. Relative to M82, lipid peroxidation was much lower and the activities of SOD, CAT and APX were higher in Lpa at 100 m M NaCl. The activity of DHAR decreased more in Lpa than in M82 under salt stress, and the activity of MDHAR, which was lower in Lpa than in M82 under control conditions, increased much more and to a higher level in salt‐treated Lpa plants. GR activity decreased similarly in the two species under salt stress. The results of these analyses suggest that the wild salt‐tolerant Lpa plants are better protected against active oxygen species (AOS), inherently and under salt stress, than the relatively sensitive plants of the cultivated species.     

冬小麦旗叶旱促衰老过程中氧化伤害与抗氧化系统的尖

研究了土壤缓慢干旱胁迫下抗旱性不同的２个冬小麦品种旗叶老过程中氧化丰以及酶促与硕果发现,在抗旱性强的品种中,冬泪科叶片旱个衰老与膜脂过氧化程度之间并无直接的联系。超氧化物歧化酶（ＳＯＤ）活性在不同抗旱性品种中均呈现持志下降的趋势,但在生强的品种中下降幅度较小,过氧化氢酶（ＣＡＴ）活性在胁迫初期基本不变,至中后期明显下降,且在抗旱性弱的品种中下降幅度较大,抗坏血酸过氧化物酶（ＡＰ）和谷胱甘肽还原酶（     

Antioxidant responses of chickpea plants subjected to boron toxicity

This study investigated oxidative stress and the antioxidant response to boron (B) of chickpea cultivars differing in their tolerance to drought. Three‐week‐old chickpea seedlings were subjected to 0.05 (control), 1.6 or 6.4 mm B in the form of boric acid (H₃BO₃) for 7 days. At the end of the treatment period, shoot length, dry weight, chlorophyll fluorescence, B concentration, malondialdehyte content and the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were measured. The 1.6 mm B treatment did not cause significant changes in shoot length of cultivars, although shoot length increased in the drought‐tolerant Gökce and decreased in the drought‐sensitive Küsmen after 6.4 mm B treatment. Dry weights of both cultivars decreased with 6.4 mm B treatment. Chlorophyll fluorescence (Fv/Fm) did not change in Gökce at either B level. Nor did it change in Küsmen with 1.6 mm B but Fv/Fm decreased with 6.4 mm B. Boron concentration in the shoots of both cultivars increased significantly with increasing levels of applied B. Significant increases in total SOD activity were observed in shoots of both cultivars given 1.6 and 6.4 mm B. Shoot extracts exhibited five activity bands, two of which were identified as MnSOD and Cu/ZnSOD. In comparison to the control group, all enzyme activities (except APX and SOD) decreased with 1.6 mm B stress. GR activity decreased, while activities of CAT, POX and APX did not change with 6.4 mm B in Küsmen. On the other hand, activities of CAT, APX and SOD increased in Gökce at both B levels. In addition, lipid peroxidation was higher in Küsmen than in Gökce, indicating more damage by B to membrane lipids in the former cultivar. These results suggest that (i) Gökce is tolerant and Küsmen is sensitive to B, and (ii) B tolerance of Gökce might be closely related to increased capacity of the antioxidative system (total SOD, CAT and APX) to scavenge reactive oxygen species and thus suppress lipid peroxidation under B stress. To the best of our knowledge, this is the first report on the antioxidant response of chickpea seedlings to B toxicity.     

Evaluation of oxidative stress tolerance in maize (Zea mays L.) seedlings in response to drought

Seedlings of selected six genotypes of maize (Zea mays L.) differing in their drought sensitivity (LM5 and Parkash drought-tolerant and PMH2, JH3459, Paras and LM14 as drought-sensitive) were exposed to 72 h drought stress at two leaf stage. Alterations in their antioxidant pools combined with activities of enzymes involved in defense against oxidative stress were investigated in leaves. Activities of some reactive oxygen species (ROS)-scavenging enzymes, catalase (CAT) and ascorbate peroxidase (APX) were enhanced in tolerant genotypes in response to drought stress. Superoxide dismutase (SOD) activity was significantly decreased in sensitive genotypes, but remained unchanged in tolerant genotypes under stress. Peroxidase (POX) activity was significantly induced in tolerant, as well as sensitive genotypes. Imposition of stress led to increase in H2O2 and malondialdehyde (MDA, a marker for lipid peroxidation) content in sensitive genotypes, while in tolerant genotypes no change was observed. Significant increase in glutathione content was observed in sensitive genotypes. Ascorbic acid pool was induced in both tolerant and sensitive genotypes, but induction was more pronounced in tolerant genotypes. Significant activation of antioxidative defence mechanisms correlated with drought-induced oxidative stress tolerance was the characteristic of the drought tolerant genotypes. These studies provide a mechanism for drought tolerance in maize seedlings.