Effects of Exogenous Auxin on the Regulation of Elongation Growth of Excised Segments of Vigna Hypocotyls under Osmotic Stress

IAA applied simultaneously with osmotica greatly enhanced theadaptive recovery of the elongation growth of segments of Vignahypocotyls during osmotic stress irrespective of whether ornot absorbable solutes were present. IAA stimulated both thesurface pump and the xylem pump, which have been shown to bestimulated by osmotic stress and to control the yielding ofthe cell wall and the absorption of solutes. Thus, wall extensibilityand the effective turgor were further enhanced under osmoticstress in the presence of IAA. These results indicate that thesimultaneous presence of IAA can reduce the inhibition of growthby osmotic stress, and they support numerical predictions basedon the apoplast canal model. The mechanism involved in the rapidrecovery of growth is discussed. ¹ Present address: Research Centre, Guangxi Agricultural University,Xiu Ling Rd., Nanning, Guangxi 530005 China. ² Present address: Biology Institute, Department of GeneralEducation, Nagoya University, 1 Furo-cho, Chikusa-ku, Nagoya,464 Japan. ³ Present address: Graduate School of Integrated Science, YokohamaCity University, 22-2, Seto, Kanazawa-ku, Yokohama, 236 Japan.     

水分胁迫下高粱叶片的渗透调节与延伸生长的关系

高粱抗旱品种3197B比不抗旱品种三尺三在水分胁迫条件下ψ_S下降低。在相同ψ_S时,3197B相对含水量高于三尺三。水分胁迫期间,3197B能始终维持比三尺三较高的ψ_P。在中度和严重水分胁迫时,3197B几种渗透物质积累均高于三尺三,其中可溶性糖和K~ 对渗透调节贡献最大。水分胁迫下,3197B正展开叶渗透调节能力较强,ψ_P维持较高,临界膨压低,叶片扩张性能小、故生长速率随ψ_W下降较慢。     

Inhibition of Gibberellic Acid-induced Elongation in Avena Stem Segments by a Substituted Pyrimidine

Avena stem segments, which respond with high amplitude, specificity, and sensitivity to gibberellic acid, were used to study the inhibition of gibberellin-induced elongation by the growth retardant alpha-cyclopropyl-alpha-(4-methoxyphenyl)-5-pyrimidine methanol (EL-531). It was found that EL-531 strongly inhibits gibberellic acid-induced elongation in this system at a concentration of 1 mm. From a double-reciprocal plot of elongation and gibberellic acid concentration, it seems that EL-531 and gibberellic acid do not compete reversibly for the same site of action. Also, because EL-531 effectively inhibits elongation in internodal tissue dissected away from the node and leaf sheath, it cannot be acting primarily by inhibiting the synthesis or transport of the leaf sheath factor(s). Because EL-531 causes lateral expansion of the stem segments as well as increased diameters of epidermal cells, in a manner very similar to the effects of colchicine, it is suggested that EL-531 inhibits gibberellic acid-induced elongation by somehow interfering with the orientation of the products of cell wall synthesis.     

Regulation of Growth in Avena Stem Segments by Gibberellic Acid and Kinetin

Kinetin at physiological concentrations causes significant reduction of GA₃-promoted growth in excised Avena stem segments. Kinetin is therefore considered to be a gibberellin-antagonist in this system. A Lineweaver-Burke plot reveals that kinetin acts non-competitively with GA₃. The kinetin inhibition of GA₃-promoted growth can be seen within 6 hours. It was found that soluble protein is markedly increased by kinetin in the tissue during the first 3 hours, thus preceding the inhibition of GA₃-promoted growth by several hours. At the cellular level, kinetin negated the blocking effect of GA₃ on cell division in the intercalary meristem portions of these segments. In fact, kinetin promotes both lateral and longitudinal cell divisions in intercalary meristem cells.     

Role of Indole-3-acetic Acid and Gibberellin in the Control of Internodal Elongation in Avena Stem Segments: Long Term Growth Kinetics

Exogenous application of indoleacetic acid results in a significant suppression of the linear growth that is promoted by exogenous gibberellic acid in Avena stem segments in a fashion similar to that previously noted in Avena leaf base segments (van Overbeek and Dowding, 1961, Fourth International Conference Plant Growth Regulation). Treatment with the auxin transport inhibitors, methyl-2-chloro-9-hydroxyfluorene-(9)-carboxylate (CFM) or 2,3,5-triiodobenzoic acid (TIBA), alone promotes elongation growth of the stem segments over that of control growth. This effect is interpreted as being due to the interference in the transport of native indoleacetic acid by CFM and TIBA, thus removing the inhibitory effect of native indoleacetic acid on gibberellin-promoted growth in the internodal intercalary meristem. This results in a greater promotion of internodal growth by native gibberellins. In the presence of (2-chloroethyl) trimethylammonium chloride (CCC), the growth-promoting effects of CFM and TIBA are decreased, and the antiauxin, PCIB (4-chloro-phenoxyisobutyric acid), has no growth-promoting effects whatsoever. These results indicate that the CFM and TIBA-promoted growth require the continuous presence of gibberellins. They further support the view that native indoleacetic acid acts as a growth suppressor hormone in its regulation of gibberellin-promoted internodal extension in Avena shoots.     

Regulation of Elongation Growth of Excised segments of Vigna Hypocotyl under Osmotic Stress in the Absence or Presence of Absorbable Solute

The regulation of elongation growth in excised segments of Vignahypocotyl under osmotic stress was investigated by means ofthe xylem perfusion and pressure-jump method. When subjectedto osmotic stress in the absence of absorbable solutes (100mM sorbitol only) or in the presence of absorbable solutes (70mM sorbitol plus 30 mM sucrose, or 70 mM sorbitol plus 15 mMKC1), the hypocotyl segments immediately began to shrink. Thehyper-polarizations of the transmembrane potentials (V_px andV_ps) took place at once. Within 40–60 minutes, the segmentsresumed growth. In the presence of absorbable solute, therewas an obvious increase in the effective turgor (Pⁱ–Y'),but the physiological wall extensibility () increased only slightly.Conversely, in the absence of absorbable solute, increasedsignificantly but (Pⁱ–Y') decreased. The results suggestthat the recovery of growth of an excised segment under osmoticstress is mainly due to the change in in the absence of absorbablesolute, and to the change in (P¹–Y') in the presence ofabsorbable solute, and that the two respiration-dependent protonpumps play important roles in these recovery processes. (Received April 28, 1989; Accepted August 24, 1989)     

IAA-Dependent Adjustment of the in vivo Wall-Yielding Properties of Hypocotyl Segments of Vigna unguiculata during Adaptive Growth Recovery from Osmotic Stress

Regulation of the in vivo yielding properties of the cell wall,namely cell wall extensibility     

Kinetics of Adaptation to Osmotic Stress in Lentil (Lens culinaris Med.) Roots

When intact roots of lentil (Lens culinaris Med.) are subjected to severe osmotic stress by treatment with a solution of low water potential, they immediately begin to shrink. Within 10 to 15 minutes, shrinkage ceases, and within 20 minutes, the roots resume growth. The time lag between application of osmoticum and resumption of growth varies from about 10 to 30 minutes over the range of external water potentials of −2 to −12.4 bars. For external water potentials as low as −8.7 bars the new steady rate of growth in the presence of osmoticum is approximately equal to that prevailing before application of osmoticum. For external water potentials between −8.7 and −13 bars growth resumes, but the new rate is less than that prior to addition of osmoticum. Measurements of changes in the internal solute content during adaptation show that the solute content of the root increases but that the magnitude of the increase is, by itself, insufficient to account for the resumption of rapid growth.     

冬青卫矛叶片质外体适应冬季胁迫的蛋白质组学分析

植物的质外体在感知外界信号和胁迫应答中起重要作用。该研究采用生理生化和蛋白质组学方法,对秋季和冬季冬青卫矛叶片的理化指标、微观结构以及叶片质外体液体中的蛋白变化进行比较分析,探索冬青卫矛叶片质外体响应冻胁迫的分子机制,以期为植物抗冻分子机制研究提供依据。结果表明:(1)冬季冬青卫矛叶片中MDA、可溶性糖含量以及SOD、POD活性均显著升高,气孔张开度减小,叶片厚度变小。(2)冬季冬青卫矛质外体液体中的蛋白质种类和含量显著高于秋季。(3)冬青卫矛叶片质外体液体中共鉴定到838个肽段和194个蛋白质;与秋季相比,冬季冬青卫矛叶片质外体液体中共筛选到43种差异积累蛋白(DAPs),其中26个蛋白质显著上调,17个蛋白质显著下调;蛋白表达模式显示,胚胎发育晚期丰富蛋白质、铁超氧化物歧化酶、过氧化物酶、丝氨酸羧肽酶等在冬季表达量较高,推测它们可能是冬季胁迫响应敏感的蛋白质。(4)KEGG富集分析显示,差异蛋白主要与应激防御、细胞壁修饰、抗病、自由基清除、甘油脂类代谢、淀粉和蔗糖代谢、次生代谢物的生物合成等生物学过程相关。(5)验证实验结果表明,冬季冬青卫矛8个差异积累蛋白与其对应的基因的表达趋势一致。研究认为,冬季冬青卫矛质外体液体中积累的蛋白可通过清除活性氧、促进单糖、寡糖和游离氨基酸等渗透调节物的生成而增强对环境的适应;推测冬青卫矛质外体中积累的单糖和寡糖可能通过增加质外体液体的浓度从而降低冰点,进而提高冬青卫矛对冬季胁迫的耐受性。     

干旱胁迫下杨树嫩茎质外体内源激素的响应

质外体与植物细胞有着不可分割的联系,其内发生的干旱胁迫响应鲜见报道,因此本文采用MD HPLC联用技术对3种杨树嫩茎质外体内源激素在干旱胁迫胁迫下的变化进行研究。结果表明: 随着干旱胁迫程度的加剧和时间的延长,3种杨树质外体GA₃、6-BA和3-IAA含量明显减少,而ABA含量极显著增加且GA₃、6-BA、3-IAA和ABA含量的变化品种间差异显著。该研究为植物干旱胁迫生理响应机制研究提供新依据,为活体、动态地定量分析质外体内源激素提供了新方法。     

The Role of Membrane Potential for the Control of Elongation Growth of Vigna Hypocotyl: Response of a Hollow Cylinder to Osmotic and Ionic Stress

We have devised an experimental system of perfusion througha hollow cylinder of a Vigna hypocotyl to examine the controlmechanism of plant stem elongation. When the cylinder was subjectedto osmotic stress, it began to shrink and then spontaneouslyresumed elongation. Not only the membrane potential differencebetween the parenchyma symplast and the central bore (V_px),but also that between the parenchyma symplast and the organsurface (V_ps), showed hyperpolarization a few minutes afterthe cylinder began to shrink. Removal of the stress caused animmediate increase in elongation rate followed by depolarizationof both membrane potentials a few minutes later. When the cylinderwas subjected to KCl stress, V_px showed transient depolarizationand recovery, while V_ps showed only immediate hyperpolarization.Increasing the KCl concentration caused V_px to depolarize, andthe cylinder simultaneously to cease to elongate for about 5min,even when the osmotic concentration of the perfusion solutionwas kept almost constant. An inverse reaction was observed whenthe KCl concentration was decreased. These two reversible responses suggest that control of V_px mayregulate the elongation of hollow cylinders, and that the xylempump plays an important role in the regulation of intact stemelongation. (Received January 7, 1987; Accepted April 30, 1987)     

Transfer RNAs Mediate the Rapid Adaptation of Escherichia coli to Oxidative Stress

Translational systems can respond promptly to sudden environmental changes to provide rapid adaptations to environmental stress. Unlike the well-studied translational responses to oxidative stress in eukaryotic systems, little is known regarding how prokaryotes respond rapidly to oxidative stress in terms of translation. In this study, we measured protein synthesis from the entire Escherichia coli proteome and found that protein synthesis was severely slowed down under oxidative stress. With unchanged translation initiation, this slowdown was caused by decreased translation elongation speed. We further confirmed by tRNA sequencing and qRT-PCR that this deceleration was caused by a global, enzymatic downregulation of almost all tRNA species shortly after exposure to oxidative agents. Elevation in tRNA levels accelerated translation and protected E. coli against oxidative stress caused by hydrogen peroxide and the antibiotic ciprofloxacin. Our results showed that the global regulation of tRNAs mediates the rapid adjustment of the E. coli translation system for prompt adaptation to oxidative stress.     

Regulation of Growth in Avena (Oat) Stem Segments by Gibberellic Acid and Abscisic Acid

The purpose of this study was to analyze the nature of the interaction between gibberellic acid (GA₃) and abscisic acid (ABA) in the regulation of growth in excised Avena (oat) stem segments. Growth, compared to sucrose controls, was inhibited by ABA in the range of 10^?4 to 10^?6M. GA₃-promoted growth was also inhibited by ABA in the same concentration range. A Lineweaver-Burk analysis of the interaction between GA₃ and ABA indicated that ABA acts in a non-competitive fashion with GA₃. This same result was obtained previously with GA₃-indoleacetic acid (IAA) and GA₃-kinetin interactions with Avena stem sections. Our results indicate that ABA can inhibit GA₃-promoted growth within physiological concentrations, and that it is probably acting at a different physiological site from that for GA₃.     

Roles of Sugar Alcohols in Osmotic Stress Adaptation. Replacement of Glycerol by Mannitol and Sorbitol in Yeast

For many organisms there is a correlation between increases of metabolites and osmotic stress tolerance, but the mechanisms that cause this protection are not clear. To understand the role of polyols, genes for bacterial mannitol-1-P dehydrogenase and apple sorbitol-6-P dehydrogenase were introduced into a Saccharomyces cerevisiae mutant deficient in glycerol synthesis. Sorbitol and mannitol provided some protection, but less than that generated by a similar concentration of glycerol generated by glycerol-3-P dehydrogenase (GPD1). Reduced protection by polyols suggested that glycerol had specific functions for which mannitol and sorbitol could not substitute, and that the absolute amount of the accumulating osmoticum might not be crucial. The retention of glycerol and mannitol/sorbitol, respectively, was a major difference. During salt stress, cells retained more of the six-carbon polyols than glycerol. We suggest that the loss of >98% of the glycerol synthesized could provide a safety valve that dissipates reducing power, while a similar high intracellular concentration of retained polyols would be less protective. To understand the role of glycerol in salt tolerance, salt-tolerant suppressor mutants were isolated from the glycerol-deficient strain. One mutant, sr13, partially suppressed the salt-sensitive phenotype of the glycerol-deficient line, probably due to a doubling of [K(+)] accumulating during stress. We compare these results to the "osmotic adjustment" concept typically applied to accumulating metabolites in plants. The accumulation of polyols may have dual functions: facilitating osmotic adjustment and supporting redox control.     

Growth Response to Ionic and Osmotic Stress of NaCl in Salt-tolerant and Salt-sensitive Maize

Salt-tolerant maize (STM) and salt-sensitive maize (SSM) were treated with 100 mM NaCI for 1,3 and 6 d and the contents of Na~+ and CI~- (cps) of different organelles of leaf cells determined by X-ray microanalysis.The results showed that Na+ and CI- entered the cytoplasm,vacuole,chloroplast and apoplast simultaneously.When STM and SSM were treated in 100 mM NaCI at atmospheric pressure (-P) and with pressure equivalent to the osmotic pressure of the NaCI (+P),the dry weights of STM (+P) and SSM (+P) plants were greater than that of STM (-P) and SSM (-P) plants,showing that the inhibitory effect of salt on plant growth was at least partially due to the osmotic effect of the NaCI.When STM and SSM were treated with NaCI and iso-osmotic polyethlene glycol,the dry weights of plants given the iso-osmotic polyethlene glycol treatment were lower for both maize lines than that of the NaCI-treated plants.Our data show that under NaCI stress,both STM and SSM seedlings simultaneously suffered from osmotic and ion stresses.     

蛋白质组学研究技术及其在植物抗渗透胁迫研究中的应用

蛋白质组学是功能基因组学研究的热点领域之一。该文介绍了蛋白质组学的基本的和新兴的研究技术方法如蛋白质组样品的制备、双向凝胶电泳、生物质谱技术、蛋白质芯片技术、酵母双杂交系统和生物信息学等,以及蛋白质组学技术在植物抗干旱、盐渍等渗透胁迫研究中的应用。     

聚乙二醇在植物渗透胁迫生理研究中的应用

介绍聚乙二醇(PEG)在调节培养液和固体培养基水势以及在水分胁迫和盐胁迫研究中的应用及应注意的问题,并介绍PEG溶液水势的测定方法和水势计算公式.     

Movement of Abscisic Acid into the Apoplast in Response to Water Stress in Xanthium strumarium L

The effect of water stress on the redistribution of abcisic acid (ABA) in mature leaves of Xanthium strumarium L. was investigated using a pressure dehydration technique. In both turgid and stressed leaves, the ABA in the xylem exudate, the `apoplastic' ABA, increased before `bulk leaf' stress-induced ABA accumulation began. In the initially turgid leaves, the ABA level remained constant in both the apoplast and the leaf as a whole until wilting symptoms appeared. Following turgor loss, sufficient quantities of ABA moved into the apoplast to stimulate stomatal closure. Thus, the initial increase of apoplastic ABA may be relevant to the rapid stomatal closure seen in stressed leaves before their bulk leaf ABA levels rise.

Following recovery from water stress, elevated levels of ABA remained in the apoplast after the bulk leaf contents had returned to their prestress values. This apoplastic ABA may retard stomatal reopening during the initial recovery period.

     

Resistance of Biofilms Formed by the Soil Bacterium Azospirillum brasilense to Osmotic Stress

Microbiology - Polyethylene glycol (PEG 6000) was used to establish osmotic stress conditions during growth of the type strain Azospirillum brasilense Sp7 and its spontaneous variants Sp7.4 and...