盐旱交叉胁迫对柽柳幼苗渗透调节物质含量的影响

以2年生柽柳幼苗为试验材料,采用盆栽模拟试验研究不同盐分和干旱胁迫对其叶片中渗透调节物质的影响,以探讨柽柳幼苗对盐旱交叉胁迫的适应性.结果表明:(1)随盐旱胁迫的不断加剧,幼苗叶片中可溶性糖含量呈先升高后降低的趋势,且中度和重度盐旱胁迫下均显著高于对照(CK).(2)幼苗叶片中脯氨酸含量在不同盐旱胁迫下均呈逐渐上升趋势,但在重度盐分和中度、重度干旱交叉胁迫下显著高于CK.(3)幼苗叶片中Na+、Cl含量在不同干旱胁迫下,随盐胁迫的加剧呈不同的变化规律,盐旱胁迫的各个处理水平下均显著高于CK,而K+、Ca2+、SO42-含量在轻度和重度干旱胁迫下随盐胁迫增强不断降低.(4)在中度盐旱胁迫下,K+、Ca2+含量与CK无明显差异.研究表明,柽柳幼苗中渗透调节物质在其抗旱耐盐性方面具有积极的调节作用;柽柳幼苗在盐旱胁迫下表现出一定的交叉适应性,适度的干旱胁迫能增强柽柳幼苗对盐分胁迫的耐受能力.     

Chloride conductance and mitochondria-rich cell density in isolated skin of Rana catesbeiana acclimated to various environments

The Cl⁻ conductance in isolated skin of frogs (Rana catesbeiana) acclimated to 30 mM solutions of NaCl, Na₂SO₄, MgCl₂ and distilled water (DW) was studied. Transepithelial potential difference (PD_trans), short-circuit current (I_SC) and total conductance (G_t) were measured under conditions such that there was Cl⁻ flux in the presence and absence of Na⁺ transport. The Cl⁻ content of the mucosal solution was acutely replaced with SO₄²⁻ or gluconate to evaluate the effect of removal of Cl⁻ conductance on electrophysiological parameters. Mitochondria-rich cell density (D_MRC) was also measured. Skins from frogs acclimated to NaCl and Na₂SO₄ showed the lowest and the highest D_MRC, respectively, but no difference could be found between the skins from frogs acclimated to DW and MgCl₂ indicating that D_MRC is not unconditionally dependent on environmental Cl⁻ in this species. Frogs acclimated to NaCl showed marked differences when compared to the other groups: the highest G_t, probably represented by a higher paracellular conductance; the lowest transepithelial electrical potential difference which remained invariant after replacement of mucosal Cl⁻ with SO₄²⁻ or replacement of mucosal Cl⁻ with gluconate and an inwardly oriented positive current in the absence of bilateral Na⁺.     

Expression of dehydration-stress-related genes in the crowns of wheatgrass species [Lophopyrum elongatum (Host) A. Love and Agropyron desertorum (Fisch. ex Link.) Schult.] having contrasting acclimation to salt, cold and drought

Agropyron desertorum and Lophopyrum elongatum were grown in a control environment or acclimated in high‐salt (daily exposure to 75 or 150 m M NaCl for 6 d), cold (6/2 °C for 14 d) or drought environments (watering withheld for 6 d). Lophopyrum elongatum was constitutively tolerant to salt and also acclimated more to salt than did A. desertorum whereas A. desertorum acclimated more to cold and drought. Dehydrin and non‐specific lipid transfer protein (nsLTP) mRNA sequences and polypeptides increased more, during acclimation to cold and drought, in A. desertorum than in L. elongatum crowns. Expression of immunologically identified dehydrin polypeptides was much higher in drought‐acclimated A. desertorum than in any other species/treatment combination. The most strongly expressed were 42 and 20 kDa. No change in dehydrin or nsLTP polypeptides were detected in the crowns during acclimation to salt. Overall, there was stronger acclimation to dehydrative stresses, at the molecular level, in A. desertorum than in L. elongatum crowns. Differences in dehydrin and nsLTP mRNA and polypeptide expression during acclimation to different stresses indicated that plants sense the differences between different primary potential causes of cellular dehydration.     

Salt stress and fluctuating light have separate effects on photosynthetic acclimation,but interactively affect biomass

In nature, soil salinity and fluctuating light (FL) often occur concomitantly. However, it is unknown whether salt stress interacts with FL on leaf photosynthesis, architecture, biochemistry, pigmentation, mineral concentrations, as well as whole-plant biomass. To elucidate this, tomato (Solanum lycopersicum) seedlings were grown under constant light (C, 200 μmol m⁻² s⁻¹) or FL (5–650 μmol m⁻² s⁻¹), in combination with no (0 mM NaCl) or moderate (80 mM NaCl) salinity, for 14 days, at identical photoperiods and daily light integrals. FL and salt stress had separate effects on leaf anatomy, biochemistry and photosynthetic capacity: FL reduced leaf thickness as well as nitrogen, chlorophyll and carotenoid contents per unit leaf area, but rarely affected steady-state and dynamic photosynthetic properties along with abundance of key proteins in the electron transport chain. Salt stress, meanwhile, mainly disorganized chloroplast grana stacking, reduced stomatal density, size and aperture as well as photosynthetic capacity. Plant biomass was affected interactively by light regime and salt stress: FL reduced biomass in salt stressed plants by 17%, but it did not affect biomass of non-stressed plants. Our results stress the importance of considering FL when inferring effects of salt-stress on photosynthesis and productivity under fluctuating light intensities.     

The Effect of Salt Stress on the Production of Canthaxanthin and Astaxanthin by Chlorella zofingiensis Grown Under Limited Light Intensity

The fresh water green microalga Chlorella zofingiensisis known to accumulate ketocarotenoids – primarily astaxanthin but also canthaxanthin – when grown under stress conditions of high light irradiance and low nitrogen. We found that salt stress can replace light stress with respect to inducing carotenoid production: cells of C. zofingiensis grown under low light irradiance and subjected to salt and low nitrogen stress accumulated higher amounts of total secondary carotenoids than those growing under high light and low nitrogen stress. Furthermore, C. zofingiensis growing under conditions of salt stress and low light accumulated higher amounts of canthaxanthin than astaxanthin. It is suggested that for canthaxanthin accumulation under salt stress, light is not a limiting factor, but for astaxanthin accumulation high light irradiance is mandatory. These results may be applied in the future for the commercial production of canthaxanthin by C. zofingiensis in systems in which light availability is poor.     

Biodegradation of lindane by a native bacterial consortium isolated from contaminated river sediment

The aerobic biodegradation of lindane (γ-hexachlorocyclohexane) by a consortium of acclimated bacteria from sediment at a polluted site on the Suquia River, Cordoba, Argentina, is reported. The bacteria were acclimated for 30 days under aerobic conditions, using a minimal culture medium containing lindane (0.034 mM) as sole carbon source. Growth of the bacterial consortium decreased at a lindane concentration of 1.03 mM and was totally inhibited at 2.41 mM. The consortium showed initial lindane degradation rates of 4.92×10⁻³, 11.0×10⁻³ and 34.8×10⁻³ mM h⁻¹ when exposed to lindane concentrations of 0.069, 0.137 and 0.412 mM, respectively. Chloride concentration increased during aerobic biodegradation, indicating lindane mineralization. A metabolite identified as γ-2,3,4,5,6-pentachlorocyclohexene appeared during the first 24 h of biodegradation. Four different bacteria, identified as Sphingobacterium spiritivorum, Ochrobactrum anthropi, Bosea thiooxidans and Sphingomonas paucimobilis, were isolated. Pure strains of B. thiooxidans and S. paucimobilis degraded lindane after 3 days of aerobic incubation. This is the first report of lindane biodegradation by B. thiooxidans.     

Increasing NaCl and CaCl<Subscript>2</Subscript> concentrations in the growth medium of quince leaves: I. Effects on somatic embryo and root regeneration

Summary The effects of increasing concentrations of NaCl and CaCl₂ on quince (Cydonia oblonga Mill. BA 29 clone) somatic embryogenesis and adventitious root regeneration were investigated. Leaves collected from in vitro-grown shoots were used as explants and induced for 2d in liquid Murashige and Skoog medium containing 11.3 μM 2,4-dichlorophenoxyacetic acid. Explants were then cultured on semisolid Murashige and Skoog medium enriched with 4.7 μM kinetin and 0.5 μM naphthaleneacetic acid under red light for 25 d and under white light for another 25 d. Two experiments were performed: in the first, NaCl was used at 0,25, 50, 100, and 200 mM in factorial combination with CaCl₂ at 3, 9, and 27 mM; in the second, NaCl was applied at 0, 5, 10, 20, 40, and 80 mM in combination with CaCl₂ at 0.3, 1.0, and 3.0 mM. Quince leaves revealed the capacity to regenerate somatic embryos and/or adventitious roots. Quantitative and qualitative regeneration from leaves was affected by NaCl treatments: increasing NaCl concentrations, in combination with CaCl₂ at 1 mM, led to an increase in the proportion of leaves producing somatic embryos only, and to a decrease of both leaves regenerating roots only and leaves simultaneously producing somatic embryos and adventitious roots. This suggests a beneficial effect of salt stress on the embryogenic process. The regeneration response decreased with increasing salt concentrations and was almost totally inhibited above 50 mM NaCl and 9 mM CaCl₂. The presence of CaCl₂ in the culture medium apparently mitigated the effects of salt stress, but only when NaCl was applied at 40 mM. NaCl at 5 mM, in the presence of 0.3 or 1 mM CaCl₂, was favorable both to somatic embryo and root production. No value of the ratio Na⁺/Ca²⁺ was found to be optimal for the regeneration processes.     

Adaptation of the obligate CAM plant Clusia alata to light stress: Metabolic responses

In the Crassulacean acid metabolism (CAM) plants Clusia alata Triana and Planch., decarboxylation of citrate during phase III of CAM took place later than malate decarboxylation. The interdependence of these two CO₂ and NADPH sources is discussed. High light accelerated malate decarboxylation during the day and lowered citrate levels. Strong light stress also activated mechanisms that can protect the plant against oxidative stress. Upon transfer from low light (200 μmol m⁻² s⁻¹) to high light (650–740 μmol m⁻² s⁻¹), after 2 days, there was a transient increase of non-photochemical quenching (NPQ) of fluorescence of chlorophyll a of photosystem II. This indicated acute photoinhibition, which declined again after 7 days of exposure. Conversely, after 1 week exposure to high light, the mechanisms of interconversion of violaxanthin (V), antheraxanthin (A), zeaxanthin (Z) (epoxydation/de-epoxydation) were activated. This was accompanied by an increase in pigment levels at dawn and dusk.     

Incorporation of 14C in the cyanobacterium Synechococcus PCC 6301 following salt stress

Synechococcus PCC 6301 synthesized sucrose as a compatible solute following hyperosmotic shock induced by NaCl. Initial rates of photosynthetic ¹⁴C incorporation were reduced following salt shock. Photosynthetic rates were comparable in cells enriched for glycogen (by growth in NO ₃ ^- -deficient medium) and cells grown in NO ₃ ^- -sufficient medium in the absence of osmotic shock. Incorporation of ¹⁴C was predominantly into the NaOH fraction and the residual acidic fraction in cells grown in NO ₃ ^- -sufficient medium, whereas incorporation was predominantly into the residual acidic fraction in cells grown in NO ₃ ^- -deficient medium. Following salt stress, ¹⁴C incorporation was initially into the ethanol-soluble fraction and the majority of tracer was recovered in sucrose. Carbon-14 was detected in sucrose in cells which had been enriched for [¹⁴C]glycogen prior to salt stress, inferring that glycogen can act as a carbon source for sucrose synthesis following salt stress. Changes in the specific activity of sucrose are consistent with an initial synthesis of sucrose from glycogen followed by synthesis of sucrose using newly fixed carbon, in response to salt stress.This work was supported by the Agricultural and Food Research Council.     

高盐生境中乌拉尔甘草盐离子分泌与积存格局的研究

采用植物水培方法,以乌拉尔甘草为研究材料,用不同浓度(0、80、160、320mmol·L~(-1))NaCl溶液胁迫处理乌拉尔甘草幼苗3周后,分析其叶片表面盐离子(K~+、Ca~(2+)、Na+)分泌速率的差异,并采集盐化低地草甸重盐土生境中2年生乌拉尔甘草植株,应用ICP-AES测定其不同部位(根、根状茎、茎、老叶和幼叶)中的盐离子(K~+、Na~+、Ga~(2+)、Mg~(2+))含量,探究盐离子在乌拉尔甘草叶片上的分泌格局以及盐离子在植株体内的积存格局,为完善甘草耐盐机理的研究提供依据。结果显示:(1)随着盐胁迫浓度的升高,乌拉尔甘草叶片上K~+、Ca~(2+)、Na+的分泌速率均呈增加趋势,且Na~+的分泌速率远远大于Ca~(2+)和K+的分泌速率。(2)在乌拉尔甘草各部位中,K+的积存量从大到小依次为:幼叶根根状茎茎老叶;Na~+在各个部位的积存量都十分有限,且无论地下部分还是地上部分,差异均不大;Ca~(2+)积存量由大到小依次为:老叶幼叶茎根状茎根,且老叶中Ca~(2+)的积存量显著高于其它部位。研究认为,在重盐碱地生境中,K+主要积存在幼叶中,Ga~(2+)主要积存在老叶中,植株体内各个部位Na~+的积存量很低,乌拉尔甘草表现出明显的拒Na现象;叶片分泌的主要盐离子为Na~+;乌拉尔甘草通过泌盐的方式将Na+排出体外,从而有效降低Na~+在体内的积存,这是其能够在重盐碱地生存生长的重要原因。     

盐碱胁迫对枸杞幼苗生物量积累和光合作用的影响

以内陆高寒区盐碱地重要的经济树种枸杞2年生幼苗为研究对象,采用盆栽控制试验方法,设置50、100、200、300mmol·L~(-1)共4个盐和碱(NaCl和NaHCO3)胁迫浓度,研究盐、碱胁迫对枸杞苗木生长和光合的影响,以明确枸杞幼苗生长的耐盐、碱浓度范围,探讨土壤盐碱含量与土壤水分含量的关系,为不同类型盐碱条件下枸杞的种植和水分管理提供理论依据。结果表明:(1)随着盐碱胁迫浓度的增大,枸杞幼苗根茎叶生物量及叶绿素含量(SPAD)、净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)和胞间二氧化碳浓度(Ci)等光合作用参数逐渐受到显著抑制,且碱胁迫的抑制作用更强烈;但低浓度(50mmol/L)NaCl胁迫下,枸杞幼苗叶绿素含量和净光合速率并未受到显著影响。(2)在盐碱胁迫条件下,枸杞幼苗的最大净光合速率(Pnmax)、暗呼吸速率(RD)、初始量子效率(AQY)、光饱和点(LSP)均低于对照,而光补偿点(LCP)高于对照,且随着胁迫浓度的增加,碱胁迫处理下的变幅大于盐胁迫。(3)随着胁迫浓度的增大,影响净光合速率的因素由气孔限制转向非气孔限制的临界值,在盐胁迫下的临界浓度约为200mmol/L,在碱胁迫下的临界浓度约为100mmol/L。(4)按照指标值超过对照组50%标准,经回归分析确定,枸杞耐盐和耐碱阈值分别为(246.3±2.1)mmol/L和(126.7±2.7)mmol/L;在此阈值的基础上,得到土壤含水量与土壤含盐量回归曲线方程。研究认为,枸杞幼苗具有一定的耐盐能力,但过高浓度的盐碱胁迫会损坏其光合结构,降低光环境适应能力和光合作用效率,从而影响其正常生长。     

Physiological acclimation to light in Chara intermedia nodes

In this study we investigated the ability of Chara intermedia to acclimate to different irradiances (i.e. “low-light” (LL): 20–30 μmol photons m⁻² s⁻¹ and “high-light” (HL): 180–200 μmol photons m⁻² s⁻¹) and light qualities (white, yellow and green), using morphological, photosynthesis, chlorophyll fluorescence and pigment analysis.Relative growth rates increased with increasing irradiance from 0.016 ± 0.003 (LL) to 0.024 ± 0.005 (HL) g g⁻¹ d⁻¹ fresh weight and were independent of light quality. A growth-based branch orientation towards high-light functioning as a mechanism to protect the plant from excessive light was confirmed. It was shown that the receptor responsible for the morphological reaction is sensitive to blue-light.C. intermedia showed higher oxygen evolution (up to 10.5 (HL) vs. 4.5 (LL) nmol O₂ mg Chl⁻¹ s⁻¹), photochemical and energy-dependent Chl fluorescence quenching and a lower Fv/Fm after acclimation to HL. With respect to qP, the acclimation of the photosynthetic apparatus depended on light quality and needed the blue part of the spectrum for full development. In addition, pigment composition was influenced by light and the Chl a/Car and Antheraxanthin (A) + Zeaxanthin (Z)/Violaxanthin (V) + A + Z (DES) ratios revealed the expected acclimation behaviour in favour of carotenoid protection under HL (i.e. decrease of Chl a/Car from 3.41 ± 0.48 to 2.30 ± 0.35 and increase of DES from 0.39 ± 0.05 to 0.87 ± 0.03), while the Chl a/Chl b ratios were not significantly affected. Furthermore it was shown that morphological light acclimation mechanisms influence the extent of the physiological modifications.     

Light-induced expression of ipt from Agrobacterium tumefaciens results in cytokinin accumulation and osmotic stress symptoms in transgenic tobacco

Cytokinins are plant growth regulators that induce shoot formation, inhibit senescence and root growth. Experiments with hydroponically grown tobacco plants, however, indicated that exogenously applied cytokinin led to the accumulation of proline and osmotin. These responses were also associated with environmental stress reactions, such as salt stress, in many plant species. To test whether increased endogenous cytokinin accumulation led to NaCl stress symptoms, the gene ipt from Agrobacterium tumefaciens, encoding isopentenyl transferase, was transformed into Nicotiana tabacum cv. SR-1 under the control of the light-inducible rbcS-3A promoter from pea. In high light (300 mol PPFD m^-2 s^-1), ipt mRNA was detected and zeatin/zeatin glucoside levels were 10-fold higher than in control plants or when transformants were grown in low light (30 mol PPFD m^-2 s^-1). High light treatment was accompanied by increased levels of proline and osmotin when compared to low light grown transformed and untransformed control plants. Elevated in planta cytokinin levels induced responses also stimulated by salt stress, suggesting either common or overlapping signaling pathways are initiated independently by cytokinin and NaCl, setting in motion gene expression normally elicited by developmental processes such as flowering or environmental stress.Abbreviations IPT isopentenyl, transferase - rbcS-3A gene encoding a small subunit protein (SSU) of Rubisco from Pisum sativum - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase     

盐分和干旱对沙枣幼苗生理特性的影响

以沙枣(Elaeagnus angustifolia L.)幼苗为实验材料,分别对其进行轻度干旱(土壤含水量7%—9%)、重度干旱(土壤含水量3%—5%)、100 mmol/L NaCl以及100 mmol/L NaCl处理下不同程度的盐旱共胁迫处理,处理2周后测其生理指标,包括生长指标、光合指标、渗透调节指标以及复水后生长指标,研究盐旱共胁迫对沙枣幼苗生理特性的影响。结果表明:和对照相比,轻度干旱对沙枣幼苗的生物量没有显著影响,重度干旱处理明显降低了沙枣的生物量,无论是轻度干旱还是重度干旱,都显著降低了沙枣幼苗的净光合速率、K~+含量,显著增加了Na~+含量、脯氨酸含量、可溶性糖含量、有机酸含量、总酚和类黄酮含量;和对照相比,100 mmol/L NaCl处理显著降低了沙枣幼苗的生物量、净光合速率和K~+含量,显著增加了Na~+含量、脯氨酸含量、可溶性糖含量、有机酸含量、总酚和类黄酮含量;和盐处理相比,轻度干旱和盐分共胁迫对沙枣幼苗的各项指标没有显著差异,而重度干旱和盐分共胁迫明显降低了沙枣幼苗的生物量、净光合速率;复水一周后,只有轻度干旱可以回复到对照水平。以上结果表明,盐分和干旱处理明显抑制了沙枣幼苗的生长,轻度干旱和盐分共胁迫条件下,沙枣幼苗表现出一定的交叉适应现象,而重度干旱却加重了盐害。     

Can elevated CO(2) improve salt tolerance in olive trees?

We compared growth, leaf gas exchange characteristics, water relations, chlorophyll fluorescence, and Na⁺ and Cl⁻ concentration of two cultivars (‘Koroneiki’ and ‘Picual’) of olive (Olea europaea L.) trees in response to high salinity (NaCl 100 mM) and elevated CO₂ (eCO₂) concentration (700 μL L⁻¹). The cultivar ‘Koroneiki’ is considered to be more salt sensitive than the relatively salt-tolerant ‘Picual’. After 3 months of treatment, the 9-month-old cuttings of ‘Koroneiki’ had significantly greater shoot growth, and net CO₂ assimilation (A_CO2) at eCO₂ than at ambient CO₂, but this difference disappeared under salt stress. Growth and A_CO2 of ‘Picual’ did not respond to eCO₂ regardless of salinity treatment. Stomatal conductance (g_s) and leaf transpiration were decreased at eCO₂ such that leaf water use efficiency (WUE) increased in both cultivars regardless of saline treatment. Salt stress increased leaf Na⁺ and Cl⁻ concentration, reduced growth and leaf osmotic potential, but increased leaf turgor compared with non-salinized control plants of both cultivars. Salinity decreased A_CO2, g_s, and WUE, but internal CO₂ concentrations in the mesophyll were not affected. eCO₂ increased the sensitivity of PSII and chlorophyll concentration to salinity. eCO₂ did not affect leaf or root Na⁺ or Cl⁻ concentrations in salt-tolerant ‘Picual’, but eCO₂ decreased leaf and root Na⁺ concentration and root Cl⁻ concentration in the more salt-sensitive ‘Koroneiki’. Na⁺ and Cl⁻ accumulation was associated with the lower water use in ‘Koroneiki’ but not in ‘Picual’. Although eCO₂ increased WUE in salinized leaves and decreased salt ion uptake in the relatively salt-tolerant ‘Koroneiki’, growth of these young olive trees was not affected by eCO₂.     

蒭雷草对盐胁迫的生理响应

该文选择从西沙东岛采集蒭雷草,通过分株繁殖挑选健壮植株作为材料,模拟热带珊瑚岛生境设置不同浓度NaCl处理,研究不同程度的盐胁迫对其植株叶片丙二醛(MDA)、抗氧化酶以及渗透调节物质的影响.结果表明:(1)短期(28 d)盐胁迫下,NaCl浓度的增加并未加速蒭雷草叶片细胞发生膜脂过氧化作用,MDA含量增加幅度较小;随着...     

Physiological and growth changes in micropropagated Citrus macrophylla explants due to salinity

Salinity is one of the major abiotic stresses affecting arable crops worldwide, and is the most stringent factor limiting plant distribution and productivity. In the present study, the possible use of in vitro culture to evaluate the growth and physiological responses to salt-induced stress in cultivated explants of Citrus macrophylla was analyzed. For this purpose, micropropagated adult explants were grown in proliferation and rooting media supplemented with different concentrations of NaCl. All growth parameters were decreased significantly by these NaCl treatments; this was accompanied by visible symptoms of salt injury in the proliferated shoots from 60 mM NaCl and in the rooted shoots from 40 mM NaCl. Malondialdehyde (MDA) increased with increasing salinity in proliferated shoots, indicating a rising degree of membrane damage. The concentration of total chlorophyll significantly decreased in the presence of NaCl, and this effect was more pronounced in the rooted explants. The Na⁺ and Cl⁻ concentrations in the explants increased significantly with the salinity level, but Cl⁻ levels were higher in the proliferated explants than in the rooted explants. For osmotic adjustment, high concentrations of compatible solutes (proline and quaternary ammonium compounds—QAC) accumulated in salt-stressed plants in proliferation, but differences were not observed in rooted explants. In proliferation, proline and QAC were highly correlated with the sodium and chloride concentrations in the explants, indicating a possible role of these compounds in osmotic adjustment. The plant concentrations of NO₃⁻, K⁺, Mg²⁺, Ca⁺ and Fe were also affected by the NaCl concentration of the medium. We suggest that the important deleterious effects in the in vitro explants of Citrus macrophylla grown at increasing NaCl concentrations were due mainly to toxic effects of saline ions, particularly Cl⁻, at the cellular level.     

Characterization of the smallest dimeric bile salt hydrolase from a thermophile Brevibacillus sp.

A thermophilic microorganism producing bile salt hydrolase was isolated from hot water springs, Pali, Maharashtra, India. This microorganism was identified as Brevibacillus sp. by 16S rDNA sequencing. Bile salt hydrolase (BSH) was purified to homogeneity from this thermophilic source using Q-sepharose chromatography and its enzymatic properties were characterized. The subunit molecular mass of the purified enzyme was estimated to be 28 kDa by SDS-PAGE and, 28.2 kDa by MALDI-TOF analysis. The native molecular mass was estimated to be 56 kDa by gel filtration chromatography, indicating the protein to be a homodimer. The pH and temperature optimum for the enzyme catalysis were 9.0 and 60°C, respectively. Even though BSH from Brevibacillus sp. hydrolyzed all of the six major human bile salts, the enzyme preferred glycine conjugated substrates with apparent K _M and k _cat values of 3.08 μM and 6.32 × 10² s⁻¹, respectively, for glycodeoxycholic acid. The NH₂-terminal sequence of the purified enzyme was determined and it did not show any homology with other bacterial bile salt hydrolases. To our knowledge, this is the first report describing the purification of BSH to homogeneity from a thermophilic source. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Salt stress induced biometric and physiological changes in Solanum tuberosum L. cv. Bintje grown in vitro

Potato plants grown in vitro were subjected to different salt stresses by providing the salts NaCl, Na₂SO₄, MgCl₂ and MgSO₄ in different concentrations up to 300 mM. Salinity greatly affected the survival and the rooting of the plants. Shoot and root growth decreased with increasing salt concentrations. Under mild stress conditions, i.e. in conditions where the plant is able to adapt to the stress, the observed decrease was dependent upon the salt used. Under severe stress conditions, however, the decrease of the shoot and root growth was independent of the nature of the ions.     

红树植物秋茄类黄酮代谢及其抗氧化活性对高盐胁迫的响应

以红树植物秋茄为试验材料,设置不同浓度NaCl(0、200和500mmol·L-1)处理的砂培实验,应用qRTPCR分析秋茄叶片中类黄酮物质合成上游的4个关键酶基因——苯丙氨酸解氨酶基因(PAL)、肉桂酸羟化酶基因(C4 H)、4-香豆酰辅酶A连接酶基因(4CL)和查尔酮合成酶基因(CHS)的转录水平,并对关键酶活性进行了分析,同时测定了幼苗生物量、钾钠离子含量、类黄酮含量及其抗氧化活性,以探讨秋茄耐盐性与类黄酮物质的关系,为揭示木本植物耐盐机制奠定基础。结果显示:(1)在盐处理条件下,秋茄叶片中PAL、4CL、C4 H和CHS4个关键酶基因的转录水平显著上调,PAL、4CL、C4H酶活性和CHS含量随着盐浓度的增加而明显上升。(2)与对照相比,秋茄根、茎、叶干重在盐处理3d和15d后均无显著变化,而秋茄株高仅在200mmol·L-1盐处理15d后显著增加,其余浓度和时间均未发现有显著性变化。(3)随着盐浓度的升高,秋茄叶片类黄酮含量显著增加,K+/Na+明显下降,丙二醛含量显著降低,活性氧自由基清除率显著增加。研究表明,盐处理加强了秋茄叶片中类黄酮代谢过程中相关酶基因的表达,类黄酮物质的累积有助于其抗氧化能力的提高,进而提高秋茄的抗盐性,维持盐胁迫下秋茄的正常生长。