Changes in antioxidative system and membrane damage of lettuce in response to salinity and boron toxicity

Individual and combined effects of salinity and B toxicity on growth, the major antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX) activities, ascorbic acid, proline, and H₂O₂ accumulation, and stomatal resistance (SR), malondialdehyde (MDA), membrane permeability (MP) and the concentrations of sodium (Na), chloride (Cl) and boron (B) of lettuce were investigated. Boron toxicity and salinity reduced growth of lettuce plants. Under B toxicity, B concentration of the plants was increased, but in the presence of NaCl, the concentration of B was significantly reduced. Sodium and Cl concentrations were increased in B + NaCl and NaCl treatments. Membrane damage was more pronounced in NaCl and B + NaCl treatments. Stomatal resistance of the plants was significantly increased by salinity treatments. The accumulation of proline and ascorbic acid was the highest in the B + NaCl treatment. In general, stress conditions significantly increased H₂O₂ and antioxidant enzyme (SOD, CAT and APX) activities. The present results indicate that stomatal closure is an important response of lettuce against NaCl and B + NaCl stress. Furthermore NaCl and B + NaCl toxicity-induced oxidative stress in lettuce resulting in lipid peroxidation and membrane damage. Increased antioxidant enzyme activities and also accumulation of ascorbic acid and proline are involved in order to overcome B- and NaCl-induced oxidative stress.     

低温胁迫对茄子幼苗APX活性的影响及cDNA序列克隆研究

[目的]探讨低温胁迫对茄子基因表达的影响。[方法]以三叶期茄子幼苗为材料,于(8±1)℃的低温下胁迫24、48、72、961、20 h,取茄子第2片叶测定APX活性及进行APX基因的cDNA克隆。[结果]结果表明:低温胁迫下APX活性先上升后下降,以胁迫处理72 h时酶活性最高;APX基因的cDNA序列测序结果显示该序列与烟草(Nicotiana tabacum L.)、菠菜(Spinacia oleracea L.)、辣椒(Capsicum annuum L.)、番茄(Lycopersicon esculentum L.)、长豇豆(Vigna unguiculata L.)、龙眼(Dimocarpus longan L.)等具有较高的同源性。[结论]APX在进化中具有较高的保守性。     

Differential response of zucchini varieties to low storage temperature

Several parameters related to cold damage in zucchini have been measured in fruits from different varieties cultivated in the province of Almería (south-eastern Spain). The purpose of this work is to correlate physiological parameters with commercial quality and chilling damage, in order to establish reliable criteria for selecting varieties having better genetic adaptation to low-temperature storage. The results show that, for varieties harvested during February, the variety Natura was the best adapted to storage at 4 °C, as its fruits suffered less from chilling injuries, had a lower weight loss, and the levels of metabolites malonyldialdehyde and H₂O₂ were not as high as in the other varieties. Genetic variation was detected for some of the parameters analysed. The positive correlation among the levels of MDA, H₂O_2, and chilling injury, as well as the negative correlation among catalase and chilling injury, makes these parameters good indicators of chilling damage in our system.     

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.     

Effect of Pichia membranaefaciens on ROS metabolism and postharvest disease control in citrus fruit

The yeast Pichia membranaefaciens has antagonistic effects against a wide range of phytopathogenic fungi that cause postharvest fruit decay. This work evaluated the effects of P. membranaefaciens on the reactive oxygen species (ROS) metabolism and disease control in harvested citrus fruit (Citrus sinensis L. Osbeck). The lesion diameter caused by Penicillium italicum and Penicillium digitatum on citrus fruit was remarkably reduced when the fruit was point-inoculated or dipped in a suspension of P. membranaefaciens at 1 × 10⁸ CFU mL⁻¹. The application of P. membranaefaciens on citrus fruit enhanced the activity of superoxide dismutase, ascorbate peroxidase, and glutathione reductase, as well as the levels of hydrogen peroxide, the superoxide anion and glutathione, but inhibited the decreasing ascorbic acid content. Furthermore, catalase activity was decreased by the same treatment. These results indicated that yeast treatment induced the synthesis of antioxidant enzymes which might have antagonistic effects against postharvest green and blue mold infection in citrus fruit.     

Overproduction of reactive oxygen species involved in the pathogenicity of Fusarium in potato tubers

Differences in virulence between Fusarium sulphureum and Fusarium sambucinum were compared. Changes in reactive oxygen species production and metabolism in inoculated slices of potato tubers were also compared. The result showed that Fusarium infection induced significant production of ROS, lipid peroxidation and loss of cell membrane integrity, but low activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX). Compared to F. sambucinum, F. sulphureum led larger lesion diameters on potato tubers and slices. It resulted in more superoxide anion ($O_2^{-}$) and earlier peak of hydrogen peroxide (H₂O₂), but lower activity of catalase (CAT) and APX, and accompanied with higher malondialdehyde (MDA) content and lower cell membrane integrity. These findings suggested that overproduction of ROS involved in the pathogenicity of Fusarium in potato tubers.     

大气O3浓度升高对麦田土壤重金属铜生物有效性和生理毒性的影响

在开放式空气O3浓度增加（FACE）平台下,采用盆栽试验,初步研究了O3浓度升高后麦田重金属Cu的生物有效性变化以及对各生长阶段小麦叶片生理毒性的影响。结果表明,在FACE条件下,小麦地上部对Cu的吸收相比于正常大气对应组有增加的现象;与正常大气对应组相比,FACE条件下土壤中有效态Cu的含量也有所增加;随着小麦的生长发育,FACE圈小麦叶片内的MDA含量总体呈上升趋势,O3升高铜污染组的小麦叶片内MDA的含量最高;与正常大气对照组相比,O3升高铜污染组的小麦叶片SOD酶和POD酶比较敏感,在分蘖期其活性受到诱导,但随着暴露时间的增加,抗氧化系统的各个酶的活性逐渐受到抑制。O3加剧了Cu对小麦的牛理胁迫．增加了Cu的牛物有效性。     

白菜型冬油菜抗坏血酸过氧化物酶(APX)基因的克隆、表达及其活性分析

抗坏血酸过氧化物酶(APX)是一种在逆境条件下清除细胞内氧自由基、增强植物抗逆性的关键酶。本研究根据已发表植物抗坏血酸过氧化物酶基因APX的同源保守序列设计引物, 采用RT-PCR扩增超强抗寒白菜型冬油菜陇油7号的DNA, 获得APX基因开放阅读框, 长度为753 bp, 编码250个氨基酸残基, 推导的氨基酸序列具有APX蛋白的典型特征。生物信息学分析显示, 与已报道的大白菜的APX氨基酸序列同源性达到99%, 该酶蛋白具有高度的进化保守性, 其保守序列属于植物的POD超家族, APX相对分子质量和理论等电点依次为27.7 kD和5.58;APX基因无信号肽, 是一个亲水性蛋白, 可推测其定位于细胞质中;二级结构预测表明陇油7号的APX是由不规则卷曲和α-螺旋组成的稳定蛋白。实时荧光定量PCR和酶活性分析显示, 该基因表达和酶活性受低温胁迫诱导, 表明该基因在白菜型冬油菜陇油7号适应低温胁迫过程中发挥重要作用。     

大白菜两个APX1基因的鉴定

利用比较基因组学的方法,从大白菜基因组中鉴定出两个与拟南芥的耐热关键基因APX1同源的基因,并对这两个基因的结构、遗传进化、顺式元件进行了分析,为下一步研究这两个基因的功能和利用这两个基因进行大白菜耐热分子育种奠定了基础。