Characterization of ascorbate peroxidase in soybean under flooding and drought stresses

Flooding and drought are the two different forms of water stress that adversely affect the growth and development of soybean plant in particular at early stage. Ascorbate peroxidase (APX) is a known antioxidant enzyme that plays key role in abiotic stresses. To investigate the changes in APX in soybean under drought and flooding stresses, western blotting, enzyme activity assay and biophoton emission techniques were used. Flooding stress was imposed by adding excess amount of water in the sand and drought by withholding water supply. Under flooding stress, a decrease in APX was detected with time. Completely opposite trend was evident in hypocotyl and root of plants exposed to drought. Western blotting and APX activity results are complementary to each other. Biophoton emissions further confirmed the increasing and decreasing trend of APX under drought and flooding stress, respectively.     

大豆GolS基因家族鉴定及盐旱胁迫下的表达分析

肌醇半乳糖苷合成酶（galactinol synthase,GolS）是棉子糖家族寡糖（raffinose family oligosaccharides,RFOs）生物合成途径中的关键酶,在植物对非生物胁迫的反应中发挥重要作用。然而,关于大豆（Glycine max）GolS基因家族成员的分子结构特征还未见研究报道。本研究在全基因组水平上鉴定了6个大豆GolS基因家族成员,并对其理化性质、染色体定位、进化关系、基因结构、保守基序、二级结构、三级结构、组织特异性表达模式以及盐和干旱胁迫下的表达量进行了分析。结果表明：6个大豆GolS基因不均匀地分布在4条染色体上,6个大豆GolS蛋白的等电点为5.45-6.08,分子量变化范围为37 567.07-38 817.59 Da,氨基酸数量为324-339 aa;亚细胞定位预测结果发现4个蛋白定位在叶绿体上,2个蛋白定位在细胞质。系统进化树分析表明,大豆GolS基因家族成员在进化树中呈现出两两紧邻的现象,在进化上较为保守。6个基因成员含有的外显子数目为3或4。二级结构和三级结构预测表明,该家族所有成员蛋白质的空间结构主要由α螺旋和无规则卷曲结构组成,有较少的β转角结构和延伸链结构。组织特异性表达分析表明,6个GmGolS家族成员在种子、根、根毛、花、茎、豆荚、根瘤和叶中均有不同程度表达。基于qRT-PCR的表达分析显示,盐旱处理后所有GmGolS基因成员表现出不同程度的上调表达,表明这些基因可能与植物的耐盐抗旱响应有关。本研究结果为后续开展大豆GolS基因的功能解析奠定了基础。     

Characterization of a novel flooding stress-responsive alcohol dehydrogenase expressed in soybean roots

Alcohol dehydrogenase (Adh) is the key enzyme in alcohol fermentation. We analyzed Adh expression in order to clarify the role of Adh of soybeans (Glycine max) to flooding stress. Proteome analysis confirmed that expression of Adh is significantly upregulated in 4-day-old soybean seedlings subjected to 2 days of flooding. Southern hybridization analysis and soybean genome database search revealed that soybean has at least 6 Adh genes. The GmAdh2 gene that responded to flooding was isolated from soybean cultivar Enrei. Adh2 expression was markedly increased 6 h after flooding and decreased 24 h after floodwater drainage. In situ hybridization and Western blot indicated that flooding strongly induces Adh2 expression in RNA and protein levels in the root apical meristem. Osmotic, cold, or drought stress did not induce expression of Adh2. These results indicate that Adh2 is a flooding-response specific soybean gene expressed in root tissue.     

Genetic manipulation of proline levels affects antioxidants in soybean subjected to simultaneous drought and heat stresses

It was assumed that the genetic manipulation of the proline (Pro) level would also affect the (homo)glutathione content as both compounds have a common precursor, glutamate. To test this hypothesis, the levels of Pro, reduced and oxidized (homo)glutathione [(h)GSH and (h)GSSG] and other antioxidants were compared under simultaneous drought and heat stress conditions and in a control treatment in a time course experiment on wild-type soybean ( Glycine max cv. Ibis) and on transgenic plants containing the cDNA coding for l -Δ¹-pyrroline-5-carboxylate reductase (EC 1.5.1.2), the last enzyme involved in Pro synthesis, in the sense and antisense directions. At the end of the recovery period, the highest H₂O₂ and lipid hydroperoxide concentrations were observed in the antisense transformants, which exhibited the greatest injury, while the lowest H₂O₂ content was detected in the sense transformants, which exhibited the lowest injury percentage. During stress treatment, the highest Pro and ascorbate (AA) levels were detected in the sense transformants, while the highest GSH and hGSH contents, AA/dehydroascorbate (DHA) and (h)GSH/(h)GSSG ratios and ascorbate peroxidase (APX) activity were found in the antisense transformants. The greatest APX (EC 1.11.1.11) activity was observed in the first part of the stress treatment in the antisense transformants, and the greatest glutathione reductase (EC 1.6.4.2) activity was observed in the second part of the treatment in the same genotype. The present experiments indicate that the manipulation of Pro synthesis affects not only the (h)GSH concentrations, but also the levels of other antioxidants.     

Identification of a highly diverged class of S-adenosylmethionine synthetases in the archaea

S-adenosylmethionine is the primary alkylating agent in all known organisms. ATP:L-methionine S-adenosyltransferase (MAT) catalyzes the only known biosynthetic route to this central metabolite. Although the amino acid sequence of MAT is strongly conserved among bacteria and eukarya, no homologs have been recognized in the completed genome sequences of any archaea. In this study, MAT has been purified to homogeneity from the archaeon Methanococcus jannaschii, and the gene encoding it has been identified by mass spectrometry. The peptide mass map identifies the gene encoding MAT as MJ1208, a hypothetical open reading frame. The gene was cloned in Escherichia coli, and expressed enzyme has been purified and characterized. This protein has only 22 and 23% sequence identity to the E. coli and human enzymes, respectively, whereas those are 59% identical to each other. The few identical residues include the majority of those constituting the polar active site residues. Each complete archaeal genome sequence contains a homolog of this archaeal-type MAT. Surprisingly, three bacterial genomes encode both the archaeal and eukaryal/bacterial types of MAT. This identification of a second major class of MAT emphasizes the long evolutionary history of the archaeal lineage and the structural diversity found even in crucial metabolic enzymes.     

SMXLs regulate seed germination under salinity and drought stress in soybean

Plant Growth Regulation - Soybeans are one of the most important crops worldwide, but yield and quality can be severely affected by abiotic stresses. Genes in the Suppressor of MAX2 1-Like (SMXL)...     

Expression of soybean plant hemoglobin gene family under abiotic stresses

Many abiotic stresses induce the generation of nitric oxide (NO) in plant tissues, where it functions as a signal molecule in stress responses. Plants modulate NO by oxidizing it to NO₃⁻ with plant hemoglobin (GLB), because excess NO is toxic to cells. At least eight genes encoding GLB have been identified in soybean, in three clades: GLB1, GLB2, and GLB3. However, it is still unclear which GLB genes are responsible for NO regulation under abiotic stress in soybean. We exposed soybean roots to flooding, salt, and two NO donors—sodium pentacyanonitrosylferrate (III) dihydrate (SNP) and S-nitroso-N-acetyl-d,l-penicillamine (SNAP)—and analyzed expression of GLB genes. GmGLB1, one of two GLB1 genes of soybean, significantly responded to both SNP and SNAP, and its induction was almost completely repressed by a NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. GmGLB1 responded to flooding but not to salt, suggesting that it is responsible for NO regulation under NO-inducing abiotic stresses such as flooding. GmGLB3, one of two GLB3 genes of soybean, did not respond to NO donors at all but did respond to flooding, at a lower level than GmGLB1. These results suggest that flooding induces not only NO but also unknown factor(s) that induce GmGLB3 gene in soybean.     

盐胁迫对大豆根系木质部压力和Na+吸收的影响

取栽培大豆的水培幼苗为材料,用木质部压力探针和原子吸收分光光度计测定了盐胁迫条件下其根木质部压力和伤流液中Na~+含量的变化,以分析大豆抗盐吸水的机制.结果表明:在25～150 mmol/L NaCl的浓度范围内,随着盐胁迫强度的增加,大豆根木质部负压力的绝对值逐渐增大,但相对负压力和根的径向反射系数则逐渐减小;木质部伤流液中Na~+含量逐渐增加,但Na~+的相对含量则逐渐降低.同时,虽然根系吸水所需的木质部负压力(压力势)及根木质部伤流液的渗透势随着盐胁迫强度的增加都有所下降,但两者共同作用使木质部水势下降的幅度远远小于根外溶液水势(渗透势)下降的幅度,即随着根外溶液盐浓度的升高,根木质部溶液的总水势逐渐高出根外溶液的水势.上述结果说明,在盐胁迫下大豆可以利用相对小的木质部负压力逆水势梯度吸水,且通过避免对Na~+的过量吸收来适应盐胁迫环境.     

Purification of S-adenosylmethionine decarboxylase from soybean.

S-Adenosylmethionine decarboxylase (EC 4.1.1.19) was purified to homogeneity from the cytosol of soybean (Glycine max) axes by ammonium sulfate fractionation, DEAE-Sepharose and methylglyoxalbis(guanylhydrazone)-Sepharose 6B chromatographies. The enzyme was free from diamine oxidase activity. The molecular weight of the enzyme estimated by gel filtration and sodium dodecyl sulfate polyacrylamide gel electrophoresis was 66,000. The Km value for S-adenosylmethionine was 0.26 mM. The optimum pH and temperature were 7.5 and 40 degrees C. Neither putrescine nor Mg2+ affected the enzyme activity, but the enzyme was inhibited by spermidine, spermine, methylglyoxalbis(guanylhydrazone), sodium borohydride and phenylhydrazine. Agmatine was a novel inhibitor which inhibited S-adenosylmethionine decarboxylase and arginine decarboxylase, preventing the accumulation of decarboxylated S-adenosylmethionine and putrescine, respectively.     

Photosynthesis, respiration and antioxidant enzymes in pepper leaves under drought and heat stresses

Leaf gas exchange, chlorophyll fluorescence and activities of antioxidant enzymes were studied in two pepper (Capsicum annuum L.) cultivars grown under drought (D) and heat (H), as well as under drought and heat in combination (HD). The drought-tolerant cv. Zhengjiao 13 exhibited greater net photosynthetic rate (P_N) and cytochrome respiratory pathway activity (R_SHAM), and lower contents of superoxide radical and hydrogen peroxide, as compared to the drought-sensitive cv. Longkouzaojiao. The P_N and R_SHAM decreased and ROS production increased under D and HD in both cultivars. As compared to the Longkouzaojiao, Zhengjiao 13 retained higher non-photochemical quenching (NPQ), photorespiration rate (R_L), and alternative respiratory pathways (R_KCN) under D and HD. Drought increased the superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities in the cytosol, chloroplasts and mitochondria in the two cultivars. Although SOD and APX activities decreased in Longkouzaojiao under HD, SOD activity increased in Zhengjiao 13. There was no H-induced reactive oxygen species production due to increase of R_L, NPQ, R_SHAM, R_KCN and activities of SOD and APX. However, H slightly decreased the P_N. The results indicated that HD was more detrimental than either stress alone.     

Morphological and ecophysiological plasticity in dioecious plant Populus tomentosa under drought and alkaline stresses

Photosynthetica - Morphological and ecophysiological traits showed by male and female Populus tomentosa Carr. trees were studied under various degrees of water and alkaline stresses. The results...     

Increased adaptive phenotypic plasticity in the introduced range in alien weeds under drought and flooding

Biological Invasions - Phenotypic plasticity is an essential mechanism by which plants respond to changes in their environment, but our understanding of the evolution of plasticity is still...     

Morphological and biochemical changes in maize under drought and salinity stresses in a semi-arid environment

Abstract

This study investigated some morphological and biochemical responses of maize to drought and salinity in open field in Tunisia with the aim of gaining insights into tolerance mechanisms. After seedling emergence, five treatments were applied until maturity: optimal water supply (control, 100% of maximum evapotranspiration - ETM); irrigation at 70% ETM (moderate drought) and at 35% ETM (severe drought); optimal supply of water containing 3?g NaCl L^?1 (moderate salinity) and 6?g NaCl L^?1 (severe salinity). Here, we demonstrated that extreme drought and salinity severely decreased the leaf area (?74% and ?55%, respectively) and the above-ground biomass (?35% and ?31%, respectively) at silking stage, indicating that the photosynthetic leaf apparatus is highly sensitive and that drought has a greater effect than salinity. Grain yield losses were also exacerbated under extreme stress conditions, viz. severe drought (?85% versus controls) and severe salinity (?73%), while productivity under moderate salinity approximated that of moderate drought, possibly due to increases in leaf chlorophyll and carotenoid content and K/Na ratio. The leaf area and its relative water content were positively correlated with grain yield under both salinity and drought stresses, and may therefore be used as markers for effective screening of maize genotypes for better stress tolerance.