Water‐stress mitigation by selenium in Trifolium repens L.

This study was designed to examine whether external selenium (Se) may improve the tolerance of Trifolium repens L. to polyethylene glycol (PEG)–induced water deficit, and to determine the physiological mechanisms of the possibly enhanced tolerance. Trifolium repens seedlings were subjected to PEG‐induced water deficit alone or combined with 5 μM Na₂SeO₄ for 24, 48, and 72 h. During the experimental period, the fresh weight (FW) of T. repens seedlings and the relative water content (RWC) of the leaves decreased gradually, and the chlorophyll concentration increased after 24 and 48 h, but decreased after 72 h. The PEG+Se‐treated plants had higher FW, RWC, and chlorophyll concentration than the PEG‐treated plants. Smaller amounts of thiobarbituric acid‐reactive substances (TBARS) and H₂O₂ accumulated in PEG+Se‐treated plants than in plants treated only with PEG. The activity of superoxide dismutase (SOD) increased gradually during the water‐deficit period, and Se application promoted SOD activity further. Catalase (CAT) activity remained unchanged after 24 and 48 h and insignificantly increased after 72 h of water deficit, whereas ascorbate peroxidase (APOX) activity increased linearly and glutathione reductase (GR) activity increased slightly over the course of treatment. Whereas the Se application exhibited no effect on the CAT activity, seedlings treated with PEG+Se had higher APOX activity during the whole experimental period and a higher GR activity after 48 and 72 h than PEG‐treated plants. These results suggest that exogenous Se treatment enhanced T. repens tolerance to PEG‐induced water deficit, and this enhancement was related to alleviation of lipid peroxidation and activation of antioxidant enzymes such as SOD, APOX, and GR.     

The role of antioxidative metabolism of tomato leaves in long‐term salt‐stress response

The antioxidative protection system as adaptation strategy to high soil salinity in the leaves of two tomato (Lycopersicon esculentum Mill.) hybrids (Buran F1 and Berberana F1) was investigated. Changes in the activity of superoxide‐dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), as well as total and oxidized ascorbate concentrations (AA and DHA) in the plant leaves subjected to three salinity levels (EC 3.80 dS m⁻¹, 6.95 dS m⁻¹, and 9.12 dS m⁻¹) relative to non‐saline control were analyzed during the fruiting phase. The obtained results clearly indicate a relation between SOD activity and AA concentration in the antioxidative protection without any peroxidase‐related H₂O₂ detoxification. Increased SOD activity accompanied by high AA concentration was noticed at all salinity levels, but the response of hybrids was specific for the particular salt concentration. The first salinity level (EC 3.80 dS m⁻¹) induced the highest level of AA in the Buran F1 (70%), while in Berberana F1 hybrid leaves the highest AA concentration (64%) was noticed at the third salinity level (9.12 dS m⁻¹). All salinity levels caused a decline in POD and APX activities in both hybrids. The possibility of a predominant role of ascorbate and SOD in the antioxidative protection of mature tomato leaves under long‐term salt stress is discussed.     

外源Ca2+、Mg2+、Cu2+和吖啶黄素对刺梨果实维生素C合成的影响

【目的】研究二价金属离子和传统抑制剂对刺梨果实维生素C合成的调控作用。【方法】以‘贵农5号’刺梨为材料,采用离体喂饲和活体注射相结合的方法,研究Ca2+、Mg2+、Cu2+等二价金属离子及吖啶黄素、石蒜碱等有机抑制剂对刺梨果实半乳糖内酯脱氢酶（GalLDH）活性和维生素C（AsA）合成的影响。【结果】Ca2+、Mg2+两种离子对初纯化的GalLDH酶活性有一定的促进作用,Cu2+则显著抑制其活性;当用金属离子与AsA合成底物半乳糖内酯（GalL）共同喂饲果肉时,Ca2+、Mg2+两种离子未有效促进AsA合成,Cu2+处理下的刺梨果肉中AsA含量甚至显著降低;在刺梨果实发育过程中,注射Ca2+对活体果实AsA合成有明显促进作用,Mg2+的作用不明显,而Cu2+依然表现出对AsA合成的抑制作用。吖啶黄素能抑制初纯化GalLDH酶液约70%的活性,而石蒜碱的抑制作用较小（约30%）,但两者在离体喂饲处理中对AsA合成表现出相似的抑制效果;活体注射处理时,吖啶黄素在处理后期对AsA合成表现出较明显的抑制作用,石蒜碱则无此效应。【结论】外源增Ca2+可促进刺梨果实AsA合成和积累,而Cu2+和吖啶黄素则有抑制作用。     

Salicylic acid induced alleviation of oxidative stress caused by clethodim in maize (Zea mays L.) leaves

Salicylic acid is used for regulation of oxidative stress in plants subjected to unfavorable environmental conditions. Application of herbicides for the purpose of weed killing can affect not only the weeds but also the main crop as well. Many herbicides have the ability to cause oxidative stress and further degradation of cell components. In this work, SA was used to alleviate the oxidative stress caused in response to clethodim herbicide in maize leaves. The results demonstrated that, spraying of clethodim caused yellowing of leaves and sometimes browning or drying of leaf tips with high clethodim doses. Contrary, leaves showed no injuries when treated with 1 mM SA 3 days prior clethodim application. Elevated amounts of H₂O₂ and MDA were detected in clethodim treated leaves compared with control indicating ROS formation and lipid peroxidation. Excessive ROS formation led to oxidative stress which followed by degradation of membranous structures. In SA treated leaves, the contents of H₂O₂ and MDA were more or less similar to the corresponding controls. A change in the antioxidant enzymes activities due to clethodim and SA treatment was noticed. For example, the activities of POD and APX were induced while SOD and CAT were more or less reduced in response to clethodim. SA treatment prior clethodim application could induce POD but inhibit CAT. Moreover, SOD and APX activities were adjusted to be similar to those of the control. Another mechanism of SA regulation of the oxidative stress occurred through the formation of antioxidants in the form of phenolic compounds. For that, spraying SA with or without clethodim could accumulate phenolic compounds greatly. The DPPH free radical scavenging assay for leaf extracts had confirmed a change in antioxidant status. Furthermore, SA could enhance accumulation of total proteins and free amino acids in clethodim and SA treated leaves compared with the control. This work was to provide evidence for the ability of SA to regulate clethodim herbicide detoxification through regulation of the antioxidant status of maize leaf cells.     

苹果果实GalDH和GalLDH基因的表达与AsA的关系

 【目的】进一步探明苹果果实是否具有抗坏血酸（AsA）合成的能力。【方法】从‘嘎拉’苹果果实中克隆AsA合成关键酶L-半乳糖脱氢酶（L-galactose dehydrogenase, GalDH）全长cDNA序列,检测它与另一合成酶L-半乳糖-1,4-内酯脱氢酶（L-galactono-1,4-lactone dehydrogenase, GalLDH）在苹果不同组织中的表达及酶活性与AsA含量的关系。【结果】克隆获得的苹果GalDH cDNA含有975 bp的完整开放阅读框,编码一条分子量为34.97kD、含324个氨基酸残基的蛋白质,登录号为GQ131419。在叶片和苹果果实不同组织中,均能检测到GalDH和GalLDH基因mRNA表达和活性,叶片高于果实,幼果高于成熟果,果皮高于果肉。同时,苹果果皮中的AsA含量受光的调控,二者在阳面果皮的表达和活性明显高于阴面果皮,而阳、阴面果肉间无明显差异。不同组织中的AsA含量与GalDH和GalLDH活性均呈显著正相关性。【结论】进一步证明了苹果果实自身具有经L-半乳糖途径合成AsA的能力,且合成可能是苹果果实AsA形成的主要决定因子。     

Differential Responses of Antioxidative Defence System to Long‐Term Field Drought in Wheat (Triticum aestivum L.) Genotypes Differing in Drought Tolerance

Drought is a severe abiotic stress and the major constraint on wheat (Triticum aestivum L.) productivity world wide. Deciphering the mechanisms of drought tolerance is a challenging task because of the complexity of drought responses, environmental factors and their interactions. The objective of this study was to evaluate the ability of the antioxidative defence system in imparting tolerance against drought‐induced oxidative stress and yield loss in two wheat genotypes, when subjected to long‐term field drought. Drought resulted in an increase in H₂O₂ accumulation and lipid peroxidation and decrease in ascorbate level in roots and leaves at different plant developmental stages. Drought‐tolerant genotype having higher antioxidative enzymes activities, and ascorbate level was superior to that of sensitive genotype in maintaining lower H₂O₂ content and lipid peroxidation and higher growth, yield and yield components under water deficit. Various antioxidative enzymes showed positive correlation with ascorbate and negative with H₂O₂ content. In developing grains, antioxidative defence response was nearly similar among both the genotypes under control condition; however, sensitive genotype failed to modulate the activities of antioxidative enzymes according to the ROS rush under field drought. Poor capacity of the antioxidative defence system in vegetative and reproductive tissues of sensitive genotype seems to be responsible, at least partly, for reduced yield potential under water deficit.     

Effect of silicon on antioxidant and stomatal response of two grapevine (Vitis vinifera L.) rootstocks grown in boron toxic,saline and boron toxic-saline soil

We investigated individual and combined effects of B toxicity and salinity in the presence or absence of silicon on the shoot growth, concentrations of sodium (Na), chloride (Cl), boron (B) and silicon (Si), and stomatal resistance (SR), lipid peroxidation (MDA), proline accumulation, H₂O₂ accumulation and the activities of major antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT and ascorbate peroxidase, APX) activity grapevine rootstocks of 41B (V. Vinifera × V. Berlandieri) and 1103P (V. Berlandieri × V. Rupestris). Applied Si counteracted the deleterious effects of salinity and boron toxicity on shoot growth by lowering the accumulation of Na in 1103P, and B and Cl in the both rootstocks. Stomatal resistance, MDA, and the concentrations of H₂O₂ and proline were higher in the plants grown in conditions of B toxicity, salinity and their combination while applied Si lowered these parameters. Lowering SOD and CAT but increasing APX, Si treatment significantly affected the enzyme activities of both rootstocks. Based on the present work, it can be concluded that Si alleviates the adverse effects of salinity, B toxicity and combined salinity-B toxicity on grapevine rootstocks by preventing both oxidative membrane damage and translocation of Na and B from root to shoots and/or soil to plant, and also lowering the phytotoxic effects of Na and B within plant tissues. When considering the antioxidative response and membrane systems, it was concluded that the rootstock 1103P was responsive to Si under stress conditions. To our knowledge, this is the first report that Si improves the combined salt and B tolerance of grapevine grown under saline, B toxic, and B toxic and saline conditions which describes membrane related parameters and antioxidant responses.     

Identification of potential molecular markers for flower sex determination in Vernicia fordii

Vernicia fordii is cultivated as an important woody oil tree, with a long history in China. It is a monoecious and diclinous species. Altering the sex ratio to increase the number of female flowers would lead to better yields. The mechanism of flower development is, however, not yet clear. In this study, the proteins that are differentially expressed between male and female flowers were isolated using a combination of two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF MS). A proteomic analysis led to the identification of 14 proteins, of which two were expressed specifically in male flowers and 10 in female flowers. Among the 10 female-specific proteins, aspartic proteinase, ascorbate peroxidase, and cyclophilin were thought to be involved in stamen abortion and gynoecium formation during the development of female flowers. Further results suggested that these proteins might be the sex-related proteins that are the potential molecular markers for flower sex determination in V. fordii.     

Effects of salt stress on ion accumulation and antioxidative enzyme activities of Oryza sativa L. and Echinochloa oryzicola Vasing

The effects of salt stress on physiological factors, such as inorganic ion absorption and antioxidative enzyme activities, of rice ( Oryza sativa L. cv. Anapurna) and Echinochloa oryzicola Vasing were investigated. Although having similar morphology, rice and E. oryzicola possessed considerably different salt-tolerance mechanisms. Echinochloa oryzicola was more salt-tolerant than rice. When exposed to salt stress (100 mmol L⁻¹ sodium chloride, NaCl; six days), E. oryzicola had the ability to limit the accumulation of sodium ions (Na⁺), maintained high potassium ion (K⁺) content and had a constantly higher K⁺/Na⁺ ratio than rice. Rice was not effective in limiting Na⁺ absorption but had a higher antioxidative capacity than E. oryzicola . The constitutive activities of superoxide dismutase (SOD) and catalase of rice were three and five times higher than that of E. oryzicola, respectively. Induced activities of SOD, ascorbate peroxidase and glutathione reductase were also higher in rice than in E. oryzicola . The high antioxidative capacity was one of the tolerance mechanisms used by rice to cope with salt stress. Therefore, the salt tolerant-mechanisms are different between the two plants.     

香蕉抗坏血酸过氧化物酶基因的克隆及表达分析

抗坏血酸过氧化物酶(Ascorbate peroxidase, APX)是植物重要的过氧化氢(Hydrogen peroxide, H2O2)清除酶之一。通过RACE(Rapid-amplification of cDNA ends)方法从香蕉根系cDNA均一化全长文库中获得一个抗坏血酸过氧化物酶基因,命名为MaAPX2基因。MaAPX2基因是香蕉APX基因编码框全长cDNA,包含一个750 bp的最大开放阅读框(Open Reading Frame, ORF),编码249个氨基酸的蛋白质。蛋白质序列结构域比对发现,在MaAPX2 N端具有典型的APX活性位点(APLMLPLAWHSA)和过氧化物酶近端血红素配体序列(DIVALSGGHTL)的保守结构域,属于典型的APX蛋白。系统进化树比对分析表明,MaAPX2与马蹄莲ZaAPX(AAC08576.1)的亲缘关系较近。组织特异性研究表明,MaAPX2基因组成型表达于香蕉各个组织,在叶片中表达量最大。在耐病和感病品种中,MaAPX2基因均上调表达,但在耐病品种中MaAPX2基因在所有时间点相对于对照增加的倍数均高于感病品种,表明该基因在香蕉的抗病性中起着重要作用。MaAPX2基因可以作为一个新的响应枯萎病侵染的标记基因。