Biosynthetic Pathways of Glycerol Accumulation under Salt Stress in Aspergillus nidulans

Redkar, R. J., Locy. R. D., and Singh, N. K. 1995. Biosynthetic pathways of glycerol accumulation under salt stress in Aspergillus nidulans. Experimental Mycology 19, 241-246. A culture of Aspergillus nidulans (FGSC 359) was gradually adapted for growth in media containing up to 2 M NaCl or was exposed to a salt shock with 2 M NaCl. The intracellular glycerol level increased by about 7.9-fold in salt-adapted and 2.4-fold in salt-shocked cultures when compared to the unadapted culture. The biosynthetic pathway involved in the accumulation of glycerol was investigated under long-term salt adaptation and short-term salt shock. Glycerol 3-phosphate dehydrogenase (EC 1.1.1.8) was induced 1.4-fold in salt-shocked but not in salt-adapted cultures. An alternate enzymatic pathway involving glycerol dehydrogenase (NADP⁺-dependent) utilizing dihydroxyacetone (DHA) and/or DL-glyceraldehyde (DL-GAD) was induced by NaCl. DHA-dependent glycerol dehydrogenase activity was induced about 6.3-fold in salt adapted and 1.35-fold in salt-shocked cultures, while DL-GAD-dependent activity was induced about 6.1-fold in salt-adapted and 1.2-fold in salt shocked cultures. However, the level of glycerol dehydrogenase activity with DL-GAD as substrate was 7% of the DHA-dependent activity. We conclude that a salt-inducible NADP⁺-dependent glycerol dehydrogenase activity electrophoretically indistinguishable from previously described glycerol dehydrogenase I results in glycerol accumulation in salt-stressed A. nidulans.     

Effect of Osmotic Stress on Carbon Metabolism in Chlamydomonas reinhardtii: Accumulation of Glycerol as an Osmoregulatory Solute

NaCl, KCl, and sucrose at equiosmolar concentrations had similar inhibitory effects on photosynthetic carbon metabolism by the freshwater green alga, Chlamydomonas reinhardtii. Inhibitory concentrations of these solutes altered the products of photosynthetic ¹⁴CO₂ incorporation, resulting in reduced incorporation into starch, sugar phosphates, lactate, and glycolate, but caused an accumulation of glycerol both intracellularly and in the medium.     

渗透胁迫对山黧豆幼苗H2O2及毒素积累的影响

用PEG经根部处理15d龄的山黧豆幼苗,取幼苗叶片为实验材料,测定过氧化氢酶(CAT)、过氧化物酶(POD)活性、过氧化氢(H     

Callus Growth and Proline Accumulation in Response to Sorbitol and Sucrose-Induced Osmotic Stress in Rice

This study investigated the influence of osmotic stress, induced by sorbitol and sucrose combinations, on growth and proline accumulation in callus cultures of rice (Oryza sativa L.). Dehusked mature seeds, cv. Hassawi, were induced to callus on MS medium supplemented with 4.52 µM 2,4-dichlorophenoxyacetic acid (2,4-D) and 2.32 µM 6-furfurylaminopurine (kinetin). The medium also contained 29.2, 58.4, 87.6, and 116.8 mM sucrose combined with 0, 54.9, 109.8, and 164.7 mM sorbitol. Callus formation was observed in about 35 % of the cultured seeds irrespective of the sugar treatment. An increase in callus mass was observed as sucrose concentration increased reaching a maximum growth at 87.6 mM. Callus growth was enhanced in response to 54.9 mM sorbitol but at higher concentration it was inhibitory. Best callus growth was obtained on a medium containing 54.9 mM sorbitol combined with 87.6 mM sucrose. Increasing osmotic stress, as a consequence of increasing sucrose and sorbitol concentrations, induced proline accumulation and the highest concentration of proline, 5.8 µmol g^–1(f.m.), was obtained on 164.7 mM sorbitol combined with 116.8 mM sucrose.     

Enhanced Trehalose Production Improves Growth of Escherichia coli under Osmotic Stress

The biosynthesis of trehalose has been previously shown to serve as an important osmoprotectant and stress protectant in Escherichia coli. Our results indicate that overproduction of trehalose (integrated lacI-P_tac-otsBA) above the level produced by the native regulatory system can be used to increase the growth of E. coli in M9-2% glucose medium at 37°C to 41°C and to increase growth at 37°C in the presence of a variety of osmotic-stress agents (hexose sugars, inorganic salts, and pyruvate). Smaller improvements were noted with xylose and some fermentation products (ethanol and pyruvate). Based on these results, overproduction of trehalose may be a useful trait to include in biocatalysts engineered for commodity chemicals.     

渗透压对产甘油假丝酵母甘油合成与胞内磷积累的影响

研究了不同磷浓度时渗透压对产甘油假丝酵母甘油合成与胞内磷积累的影响。结果表明,不同磷含量时,产甘油假丝酵母甘油合成越多,分泌至胞外和积累于胞内的甘油也越多,其最大甘油合成量存在一个最适渗透压。同样;在相同渗透压下,其最大甘油合成量也存在一个最适磷浓度。在相同磷含量时,渗透压增高能够促进胞内聚磷酸盐积累;当渗透压相同时,培养基中磷含量增加,胞内游离磷和聚磷酸盐均增加。在生长稳定期后期,富磷可以促进胞内游离磷和聚磷酸盐积累显著增加。经分析发现,产甘油假丝酵母胞内积累甘油与聚磷酸盐,可能对克服对数生长期细胞数量少而渗透压胁迫大的困境发挥了极其重要的作用,从而能维持其生长稳定期较高的生物量、细胞存活率和甘油产量。     

Accumulation of Trehalose as a Compatible Solute under Osmotic Stress in Euglena gracilis Z

ABSTRACT. The photosynthetic protozoon Euglena gracilis, accumulated a large amount of trehalose in the cells under salt or osmotic stresses. Radioactivity of [14C] paramylon, a β-1,3-polyglucan which was stored in the cells of E. gracilis. was degraded rapidly and this radioactivity was almost stoichiometrically incorporated into trehalose. The interconversion of trehalose from paramylon by salt or osmotic stresses was dependent on the concentrations or osmotic pressures, suggesting that E. gracilis accumulate trehalose as an osmoprotectant. After the removal of salt or osmotic stresses, trehalose was gradually degraded, however, it was not converted into paramylon.     

干旱胁迫对甘草幼苗生长和渗透调节物质含量的影响

采用人工控制水分模拟干旱的处理方法,研究了干旱胁迫对甘草幼苗生长状况、水分状况和主要渗透调节物质含量的影响.结果显示:轻度干旱胁迫有利于甘草幼苗根系生长,植株根冠比加大.干旱胁迫下甘草根叶组织中相对含水量下降,束缚水/自由水升高.甘草幼苗组织中渗透调节物质可溶性蛋白、游离脯氨酸、可溶性糖含量在干旱胁迫下也均显著增加;且...     

Casein Micelle Dispersions under Osmotic Stress

Casein micelles dispersions have been concentrated and equilibrated at different osmotic pressures using equilibrium dialysis. This technique measured an equation of state of the dispersions over a wide range of pressures and concentrations and at different ionic strengths. Three regimes were found. i), A dilute regime in which the osmotic pressure is proportional to the casein concentration. In this regime, the casein micelles are well separated and rarely interact, whereas the osmotic pressure is dominated by the contribution from small residual peptides that are dissolved in the aqueous phase. ii), A transition range that starts when the casein micelles begin to interact through their κ-casein brushes and ends when the micelles are forced to get into contact with each other. At the end of this regime, the dispersions behave as coherent solids that do not fully redisperse when osmotic stress is released. iii), A concentrated regime in which compression removes water from within the micelles, and increases the fraction of micelles that are irreversibly linked to each other. In this regime the osmotic pressure profile is a power law of the residual free volume. It is well described by a simple model that considers the micelle to be made of dense regions separated by a continuous phase. The amount of water in the dense regions matches the usual hydration of proteins.     

NaCl胁迫对流苏幼苗生长、钠钾离子分布及渗透调节物质的影响

以2年生的流苏播种苗为材料,采用不同浓度(50、100、200、300 mmol·L^-1)NaCl溶液进行胁迫处理,研究盐胁迫对流苏的生长、Na^+和K^+分布格局、渗透调节物质的影响,以明确其耐盐阈值。结果表明:(1)随着NaCl胁迫浓度的增加,流苏幼苗生长量逐渐降低,盐害指数升高、存活率下降;幼苗耐盐阈值为98.693 mmol·L^-1(0.577%W/V)。(2)随着NaCl胁迫浓度的增加,流苏幼苗各器官中的Na^+含量持续增加,并在浓度为50 mmol·L^-1时表现为根>叶>茎,在其余各处理组表现为叶>根>茎;幼苗根、叶中的K^+含量表现为先增后减的变化趋势,茎中K^+含量总体表现为下降趋势,且器官中K^+含量表现为根>叶>茎;幼苗根部到茎部和茎部到叶部的离子选择性运输能力、各器官中的K^+/Na^+比值均呈下降趋势。(3)随着NaCl浓度的增加,流苏幼苗叶片可溶性糖、可溶性蛋白含量总体呈上升趋势,其脯氨酸含量呈先上升后下降的趋势。研究发现,流苏幼苗根系可通过对Na^+的吸收和累积来阻止其向地上部运输进而避免盐害发生;叶片和茎中通过提高对K^+的选择性吸收和累积,从而增大K^+/Na^+比值以减缓盐分对其生理代谢的伤害。     

渗透胁迫对杜氏盐藻胞内甘油含量及相关酶活性影响

杜氏盐藻（Dunaliella salina）是一种抗渗透能力强的单细胞绿藻,甘油在其渗透调节过程中发挥重要作用。本实验对5种不同NaCl浓度条件下,盐藻的生长、细胞内甘油含量及甘油代谢相关酶的活性变化进行了测定。结果表明,NaCl浓度过高或过低均影响盐藻的生长;高渗胁迫条件下甘油含量迅速增加,3-磷酸甘油磷酸酶的活性和二羟丙酮还原酶催化二羟丙酮转化为甘油的活性明显增加;而低渗胁迫条件下的甘油含量会迅速降低,3-磷酸甘油磷酸酶的活性丧失,二羟丙酮还原酶催化甘油转化为二羟丙酮的活性增加。基于此实验结果,我们对盐藻渗透胁迫条件下细胞内的甘油代谢过程与其抗渗透胁迫能力的相关性进行了探讨。     

Turgor, Growth and Rheological Gradients of Wheat Roots Following Osmotic Stress

The growth rate of hydroponically grown wheat roots was reducedby mannitol solutions of various osmotic pressures. For example,following 24 h exposure to 0·96 MPa mannitol root elongationwas reduced from 1· mm h^–1 to 0·1 mm h^–1 Mature cell length was reduced from 290 µm in unstressedroots to 100 µm in 0·96 MPa mannitol. This indicatesa reduction in cell production rate from about 4 per h in theunstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4·5 mm in unstressedroots but became shorter as growth ceased in the proximal regionsat higher levels of osmotic stress. The turgor pressure along the apical 5·0 mm of unstressedroots was between 0·5 and 0·6 MPa but declinedto 0·41 MPa over the next 50 mm. Following 24 h in 0·48(200 mol m^–3) or 0·72 MPa (300 mol m^–) mannitol,turgor along the apical 50 mm was indistinguishable from thatof unstressed roots but turgor declined more steeply in theregion 5·10 mm from the tip. At the highest level ofstress (0·96 MPa or 400 mol m^–3 mannitol) turgordeclined steeply within the apical 20 mm. Key words: Growth, turgor pressure, wall rheology, osmotic stress, osmotic adjustment     

渗透胁迫对杜氏盐藻胞内甘油含量及相关酶活性影响

杜氏盐藻(Dunaliella salina)是一种抗渗透能力强的单细胞绿藻, 甘油在其渗透调节过程中发挥重要作用。本实验对5种不同NaCl浓度条件下, 盐藻的生长、细胞内甘油含量及甘油代谢相关酶的活性变化进行了测定。结果表明, NaCl浓度过高或过低均影响盐藻的生长; 高渗胁迫条件下甘油含量迅速增加,3-磷酸甘油磷酸酶的活性和二羟丙酮还原酶催化二羟丙酮转化为甘油的活性明显增加; 而低渗胁迫条件下的甘油含量会迅速降低, 3-磷酸甘油磷酸酶的活性丧失, 二羟丙酮还原酶催化甘油转化为二羟丙酮的活性增加。基于此实验结果, 我们对盐藻渗透胁迫条件下细胞内的甘油代谢过程与其抗渗透胁迫能力的相关性进行了探讨。     

盐胁迫对药用蒲公英生长特性及有效成分积累与离子吸收分配效应的影响

以药用蒲公英(Taraxacum officinale)为试材,研究不同浓度盐胁迫对其生长特性、有效成分积累和离子吸收分配的影响。结果表明,低盐胁迫(0.1%NaCl)对药用蒲公英生长和菊苣酸含量无显著影响,叶中Na⁺含量与对照无显著差异,K⁺含量及K⁺/Na⁺显著升高;高盐胁迫(≥0.2%NaCl)下其生长受到显著抑制,菊苣酸含量显著降低,类囊体膜结构随着盐胁迫加剧趋于紊乱,光合能力减弱,叶片Na⁺含量显著上升,而K⁺、Ca²⁺和Mg²⁺含量下降,K⁺/Na⁺、Ca²⁺/Na⁺和Mg²⁺/Na⁺显著降低。离子运输选择性系数(S_Ca,Na、S_Mg,Na、S_K,Na)随着盐胁迫加剧呈先升后降趋势。相关性分析表明,盐胁迫下...     

渗透胁迫对高粱根中K~+累积的刺激作用

本工作中发现,2,4—二硝基酚(DNP)可有效地洗去高粱根中的K~+,从而提高了测定和比较K~+累积量的显示度和准确性,渗透胁迫下,高粱根中K~+的累积量比对照增加高达6.7倍;同时,组织的H~+分泌明显受到促进,动力学研究表明,经PEG胁迫的高粱根对K~+的亲和力显著增强。对照:K_m=9.25mmol/L,V_m=23.6μmolg~(-1)DW min~(-1);PEG处理者:K_m=27.25μmol/L,V_m=14.71μmolg~(-1)DW min~(-1).地上部的存在有利于 K~+的吸收。渗透胁迫所促进的K~+吸收可被亚胺环己酮(CHM)完全抑制,这一结果暗示渗透胁迫诱导的K~+吸收的增加依赖于蛋白质的诱导合成,本文讨论了K~+吸收增强的可能机理。     

渗透胁迫下小麦根系渗透调节与根冠淀粉水解的研究

用不同浓度的PEG—600对抗旱性不同的小麦幼苗进行渗透胁迫处理,研究了小麦幼苗根系的淀粉酶活性、可溶性糖含量、渗透势、渗透调节能力和根冠淀粉的水解状况。结果表明,随着渗透胁迫程度的加重,抗旱性强的小麦品种昌乐5号和北农2号根系渗透势和饱和渗透势的降低程度大于抗旱性弱的小麦品种鲁麦5号和921842,并且抗旱性强的小麦品种根系的渗透调节能力大于抗旱性弱的小麦品种。随着渗透胁迫程度的加重．各品种小麦根冠淀粉粒均有不同程度的减少。而抗旱性强的品种根冠淀粉粒的减少程度小于抗旱性弱的品种;抗旱性强的小麦品种根系淀粉酶活性显著高于抗旱性弱的小麦品种,但是,随着渗透胁迫程度的加重,抗旱性弱的品种淀粉酶活性增加的幅度远高于抗旱性强的品种。可溶性糖含量的变化趋势与淀粉酶活性的变化趋势一致．即渗透胁迫下根冠淀粉水解程度大的小麦品种,可溶性糖的含量高。但根冠淀粉水解在根系的渗透调节以及在小麦适应水分胁迫中的作用还有待于进一步探讨。     

渗透胁迫和缺磷对小麦幼苗生长的影响

水培条件下缺磷小麦幼苗的叶片含水量和叶绿素含量显著降低,丙二醛含量增加,小麦幼苗生长受抑,地上部分生长受到的影响大于根系,上述指标的变化幅度还与缺磷程度呈正相关,且不耐低磷品种中国春大于耐低磷品种烟中144。在相同条件下,渗透胁迫和缺磷两者表现出胁迫加剧的现象。     

Preferential Osmolyte Accumulation: a Mechanism of Osmotic Stress Adaptation in Diazotrophic Bacteria

A common cellular mechanism of osmotic-stress adaptation is the intracellular accumulation of organic solutes (osmolytes). We investigated the mechanism of osmotic adaptation in the diazotrophic bacteria Azotobacter chroococcum, Azospirillum brasilense, and Klebsiella pneumoniae, which are adversely affected by high osmotic strength (i.e., soil salinity and/or drought). We used natural-abundance ¹³C nuclear magnetic resonance spectroscopy to identify all the osmolytes accumulating in these strains during osmotic stress generated by 0.5 M NaCl. Evidence is presented for the accumulation of trehalose and glutamate in Azotobacter chroococcum ZSM4, proline and glutamate in Azospirillum brasilense SHS6, and trehalose and proline in K. pneumoniae. Glycine betaine was accumulated in all strains grown in culture media containing yeast extract as the sole nitrogen source. Alternative nitrogen sources (e.g., NH₄Cl or casamino acids) in the culture medium did not result in measurable glycine betaine accumulation. We suggest that the mechanism of osmotic adaptation in these organisms entails the accumulation of osmolytes in hyperosmotically stressed cells resulting from either enhanced uptake from the medium (of glycine betaine, proline, and glutamate) or increased net biosynthesis (of trehalose, proline, and glutamate) or both. The preferred osmolyte in Azotobacter chroococcum ZSM4 shifted from glutamate to trehalose as a consequence of a prolonged osmotic stress. Also, the dominant osmolyte in Azospirillum brasilense SHS6 shifted from glutamate to proline accumulation as the osmotic strength of the medium increased.     

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.