微生物耐铝机制的研究进展

铝毒是酸性土壤中限制作物生产最主要的因素。微生物与铝作用逐渐受到关注,一些微生物特别是模式微生物的耐铝机制已被提出。主要综述了酵母,假单胞菌及其它微生物耐铝机制的研究进展,并展望了微生物耐铝机制研究发展的方向。     

微生物铝毒和耐铝机制的研究现状

铝是地球上含量最为丰富的金属元素 ,在酸性条件下 ,主要以Al3 存在。Al3 作为一种严重的环境毒剂 ,已经在众多模式生物中所证明。近年来 ,许多生物学家已日益注意到铝毒和耐铝性在环境科学与生命科学领域的重要性。结合研究工作 ,综述了微生物铝毒害和耐铝的机制。微生物通过①增强分泌有机酸与Al3 螯合 ,②超表达Mg2 通道蛋白 ,增强细胞转运吸收Mg2 ,③通过线粒体ATPase和液泡ATPase协同作用将Al3 隔离于液泡内 ,以及④通过氧化胁迫改变、调节Al3 毒害和耐铝性 ,减缓Al3 对细胞的毒害。     

植物铝毒害及遗传育种研究进展

本文简单概述了目前植物铝毒害及遗传育方面的研究进展,Al^3 可以通过与细胞骨架的作用,影响根的正常生理功能和形态建成,植物可以通过根尖分泌有机酸或磷酸等将离子态的为成螯合态的铝,通过吸收H^ 提高根尖周围的pH,将Al^3 变成难溶性的Al(OH)3或磷酸铝从而解 除铝毒害,也可以通过在细胞内与Ａl^3 形成无毒害的复合结构从而解除铝毒害,国外通过基因工程和突变体筛选已经获得了一批耐铝的植物材料,国内一些研究者通过变体筛选也获得了一些耐铝的植物材料,对植物耐铝性的遗传研究表明,植物的耐铝性既可以是受单基因控制的,也可以是受多基因控制的。     

植物耐铝的生理机制

就植物本身的解除铝毒生理机制、铝毒与膜整合阴离子通道、铝毒与有机酸代谢相关酶、转基因与植物耐铝性的提高、耐铝基因的QTL以及参与铝毒响应的信号转导机制的研究进展作介绍。     

植物铝毒害及遗传育种研究进展

本文简单概述了目前植物铝毒害及遗传育种方面的研究进展。Al3+可以通过与细胞骨架的作用,影响根的正常生理功能和形态建成。 植物可以通过根尖分泌有机酸或磷酸等将离子态的铝变成螯合态的铝,通过吸收H+提高根尖周围的pH,将Al3+变成难溶性的 Al(OH)3或磷酸铝从而解除铝毒害, 也可以通过在细胞内与Al3+形成无毒害的复合结构从而解除铝毒害。国外通过基因工程和突变体筛选已经获得了一批耐铝的植物材料,国内一些研究者通过突变体筛选也获得了一些耐铝的植物材料。 对植物耐铝性的遗传研究表明, 植物的耐铝性既可以是受单基因控制的,也可以是受多基因控制的。     

口腔微生物耐氟机制的研究进展

氟化物一直被当作一种有效的抗龋药物广泛应用,但长期使用氟化物可能会导致耐氟菌株的出现,使其通过表型适应或基因型改变对氟产生抗性,降低氟化物防龋效果,且长期氟干扰可能引起口腔微生态失衡,从而诱发疾病。鉴于氟与口腔疾病防治的密切关系,以及口腔微生物稳态对于口腔乃至全身健康的重要作用,本文就口腔微生物耐氟机制的研究进展作一综述。     

植物地上部对铝毒的生理响应及其耐性

全世界50％以上潜在的可耕地属于酸性土壤,铝毒害是酸性土壤上植物生长最有害因素之一。近年来,为了阐明植物铝毒害及其耐性,前人已进行了大量的研究,并有一些综述性文章发表。然而,大多数文章主要综述铝对植物根系的影响及其耐性,因为根生长受抑是最早的铝毒害症状之一和溶液培养时最容易辨认的铝毒害症状。为此,本文综述了铝对植物地上部光合作用、光保护系统、水分利用效率、含水量、碳水化合物含量、矿质营养、有机酸和氮代谢的影响,并对富铝植物的解铝毒机制（铝与小分子有机酸螯合和把铝隔离在对铝不敏感的表皮细胞和液泡内）进行了综述。本文还对植物耐铝遗传学和分子生物学及今后需要研究的问题进行了讨论。     

酸性土壤中耐铝细菌的筛选鉴定及其耐铝能力分析

以含有1mmol／LAl3＋的s—LB培养基作为筛选培养基,从酸性土壤中分离到13株耐铝的细菌菌株,选取其中6株进行形态学分析,结果观察到这些菌株的菌体均呈杆状,其中1株为革兰阳性反应,其余5株为革兰阴性反应。以细菌通用引物扩增这些菌株的16SrDNA并测序,将得到的序列与GenBank中的序列进行BLAST比对,利用MEGA4．0软件,按照Neighbor-joining法构建系统进化树,这6个菌株分别与Enterobacter endosymbiont,Serratia marcescens ,Pantoea agglomerans ,Enterobacter aerogenes .Bacillus subtilis 和 Enterobacter asburiae的亲缘关系最近。将这些菌株接种到加有2mmol／LAl3＋、pH4．5的s—LB固体培养基上培养时,它们都能生长,说明这些菌株具有较好的耐铝能力,这些菌株为进一步研究细菌的耐铝机制提供了极好的材料。     

铁对缺磷和铝毒耦合胁迫下杉木耐铝性的影响

为探究酸性土壤中铁与缺磷和铝毒耦合胁迫的互作关系及其对杉木耐铝性的影响,以杉木优良基因型YX11实生苗为材料,采用控制条件下沙培试验方法,设置对照(CK)、铝胁迫(Al)、缺磷和铝毒耦合胁迫(-P+Al)、缺磷和铝毒耦合胁迫下缺铁处理(-P+Al-Fe),研究缺磷和铝毒耦合胁迫下,外源供铁对杉木幼苗生长、光合生理、植株铝和铁含量、叶片抗性生理的影响。结果表明:(1)Al胁迫处理能显著抑制杉木幼苗生长,-P+Al处理进一步加剧Al诱导的生长受抑,而-P+Al-Fe处理则能显著缓解-P+Al处理引起的生长受抑程度。(2)杉木叶片光合色素含量,叶绿素荧光参数最大荧光(F_(m))、可变荧光(F_(v))、PSⅡ潜在光化学活性(F_(v)/F_(o))、PSⅡ最大光化学效率(F_(v)/F_(m))、光化学淬灭系数(qP)和实际最大量子产额(QY)以及叶片净光合速率在不同胁迫处理下均较CK出现不同程度下降,但-P+Al处理的降幅显著大于-P+Al-Fe处理。(3)杉木叶片SOD、POD、CAT和APX等抗氧化酶活性在不同胁迫处理下均比CK显著增加,但-P+Al处理各抗氧化酶活性增幅显著低于-P+Al-Fe处理,从而导致-P+Al处理叶片形成更多过氧化氢,积累大量丙二醛。(4)杉木根和叶片铝含量在不同胁迫处理下均比CK显著增加,但根和叶片中铝含量在-P+Al-Fe和-P+Al处理间无显著差异,而-P+Al处理根和叶片中铁含量显著高于-P+Al-Fe处理。研究发现,在缺磷和铝毒耦合胁迫下,与缺铁相比,正常供铁能显著促进铁在杉木植株体内的积累,抑制其抗氧化酶活性的增强,促进过氧化氢大量积累,造成光合色素降解,同时对质膜和光合反应中心造成不可逆损伤,显著降低光合效率,加剧铝毒诱导的杉木生长受抑程度。     

分离和收集耐铝植物细胞的方法

日本Ｙａｍａｇａｔａ大学的科学家Ｔ．Ｗｎｇａｔｓｕｍａ及其同事描述了一种从铝－耐受和铝－敏感植物细胞混合物中收集耐铝植物细胞的新技术。基于以前发现耐铝品种的原生质体比铝－敏感品种的原生质体质膜表面的负电荷少,Ｗａｇａｔｓｕｔｍａ小组用新准备的带正电的二氧化硅小珠与来源于水稻（Ａｌ－耐受）,玉米（中等Ａｌ－耐受）或豌豆（Ａｌ－敏感）根细胞的纯化原生质体混合,然后以一个Ｆｉｃｏｌｌ不连续梯度高心混合物。他们从离心管底部级分得到来自铝－耐受植物（水稻）的原生质体,从上部级分得到来自铝－敏感植物（豌豆）…     

Continuous flow rhizostat for the study of aluminum toxicity

Abstract. Wide variations in total aluminum (AL) concentration reported to have a toxic effect on plants arc attributed to imprecise definition of the chemical environment at the root interface. Because AL can complex with natural ligands and form time-dependent metastable species in water, the requirements of a fixed AL speciation in the nutrient medium can only be met by simultaneously holding constant the pH, the AL/OH ratio and the renewal time of the solution. It is also important that the root be constantly perfused by a fresh solution so that the root interface is as chemically close to the bulk solution as possible. The rhizostat presented here uses a process controller to constantly replenish four tanks containing different combinations of nutrients and AL. The solution is pumped from each tank to a tray where it is continuously delivered to seedlings growing on artificial medium. This rhizostat provides an accurate control for AL speciation. Preliminary experiments on white spruce seedlings show that levels of 10 micromolal or less total AL are sufficient to cause toxic effects at pH of 4.5 and without the formation of AL complexes.     

Interactive regulation of nitrogen and aluminum in rice

Despite many studies on the high aluminum (Al) tolerance of rice (Oryza sativa), its exact mechanisms remain largely unknown. It is also unclear why Al improves growth of some plants. Our research on interactions between nitrogen (N) and Al may help to understand these phenomena. Previously, we found that ammonium-supplemented rice was more Al tolerant than nitrate-supplemented rice. Furthermore, Al-tolerant rice varieties preferred ammonium, while Al-sensitive ones preferred nitrate; in fact, Al tolerance was significantly correlated with the ammonium/nitrate preference among rice varieties. Al even enhanced growth of ammonium-supplemented rice, while it inhibited growth of nitrate-supplemented rice. Based on our own and other reports on N-Al interactions, we propose that intermediate products of N metabolism may play a role in rice Al tolerance. Al-enhanced ammonium utilization may explain why Al promotes growth of some plants, since Al often coexists with higher levels of ammonium than nitrate in acid soils.     

Buffered,phosphate-containing media suitable for aluminum toxicity studies

Studies of Al rhizotoxicity sometimes require the use of well-defined rooting media. For that reason, buffers and phosphate are often omitted from Al solutions for which species composition must be determined precisely. Homopipes and succinate appear to be suitable buffers for short-term studies with seedlings of an Al-sensitive wheat (Triticum aestivum L. cv. Scout 66) and white clover (Trifoliau repens L. cv. Huia). In the case of homopipes (homopiperazine-N,N-bis-2-[ethane-sulfonic acid]), a slight inhibition of root elongation must be taken into account, but no binding of Al³⁺ was observed. In the case of succinate, no inhibition of root elongation was observed, but Al³⁺ binding must be considered. Phosphate-containing media remain free of solid-phase or polynuclear species whenever {Al³⁺}²{HPO₄ ^2-}{OH^–}³ < 10^–47.0 (or {Al³⁺}{HPO₄ ^2-}{OH^–}< 10^–22.7) and when {Al³⁺}³ / {H⁺}³ < 10^8.8. These ion activity products, that define stable Al solutions in the laboratory, appear to apply in soils also, according to an analysis of published data. The published equilibrium values {AlH₂PO₄ ²⁺} / ({Al³⁺}{H₂PO₄ ^–}) = 10^3.0, {AlHPO₄ ⁺} / ({Al³⁺}{HPO₄ ^2-}) = 10^7.0, and {Alsuccinate⁺} / ({Al³⁺}{succinate ^2-}) = 10^4.62 appear to be suitable, because solution toxicity could be accounted for entirely on the basis of computed Al³⁺ even in solutions containing high levels of Alsuccinate⁺ and AlHPO₄ ⁺ (in every case {AlHPO₄ ⁺}>> {AlH₂PO₄ ²⁺}). Thus, AlHPO₄ ⁺ and Alsuccinate⁺ were not toxic at achieved concentrations.     

Study of aluminum toxicity by means of vital staining profiles in four cultivars of Phaseolus vulgaris L

Aluminum toxicity is a very important factor limiting crop productivity on acid soils. Early effects of aluminum toxicity comprise inhibition of cell division and effects on root elongation. The plasma membrane can be the primary target of aluminum toxicity and thus, vital staining techniques could be a powerful tool in determining effects of metal stress on the plasma membrane.

In this paper, we discuss the effects of Al on growth and membrane integrity by staining root tips with a mixture of fluorescein diacetate and propidium iodide.

The results show a good correlation between results from growth measurement and the vital staining. From the comparison of the luminosity patterns generated by vital staining it is easy to determine Al-resistant varieties, revealing this technique as a powerful and fast method for determining tolerance to Al in different varieties.     

Inexpensive biological tests for soil calcium deficiency and aluminum toxicity

Two relatively simple procedures based on 4-day seedling growth were developed for identifying soil calcium (Ca) deficiency and/or aluminum (Al) toxicity. Test A uses any large-seeded cultivar that a farmer might consider planting and reveals whether the cultivar will suffer from Ca deficiency by comparing root growth in untreated soil to that in soil receiving a minimal Ca addition (0.1 meq.100mL⁻¹ soil), sufficient to eliminate possible deficiency. Al toxicity is detected by comparing root growth in a sample receiving the minimal Ca treatment with growth in the soil treated with enough lime to neutralize exchangeable Al. In test B, potential Al toxicity problems are detected for any widely-grown standard crop by comparing its growth with that of a different, Al-tolerant variety on soil samples receiving 0.1 meq.100mL⁻¹ Ca. With this test Ca deficiency in the untreated sample is detected by an increase in root growth of the Al-tolerant variety resulting from a small addition of Ca. The tests agreed with diagnoses made by standard chemical methods in about 84% of the cases examined. The proposed tests can be carried out using simple, easily-available materials without the necessity of sending soils to an analytical laboratory.     

The evolution of glutathione metabolism in phototrophic microorganisms

Summary Of the many roles ascribed to glutathione (GSH) the one most clearly established is its role in the protection of higher eucaryotes against oxygen toxicity through destruction of thiol-reactive oxygen byproducts. If this is the primary function of GSH then GSH metabolism should have evolved during or after the evolution of oxygenic photosynthesis. That many bacteria do not produce GSH is consistent with this view. In the present study we have examined the low-molecular-weight thiol composition of a variety of phototrophic microorganisms to ascertain how evolution of GSH production is related to evolution of oxygenic photosynthesis. Cells were extracted in the presence of monobromobimane (mBBr) to convert thiols to fluorescent derivatives, which were analyzed by highpressure liquid chromatography. Significant levels of GSH were not found in the green bacteria (Chlorobium thiosulfatophilum andChloroflexus aurantiacus). Substantial levels of GSH were present in the purple bacteria (Chromatium vinosum, Rhodospirillum rubrum, Rhodobacter sphaeroides, andRhodocyclus gelatinosa), the cyanobacteria [Anacystis nidulans, Microcoleus chthonoplastes S.G., Nostoc muscorum, Oscillatoria amphigranulata, Oscillatoria limnetica, Oscillatoria sp. (Stinky Spring, Utah),Oscillatoria terebriformis, Plectonema boryanum, andSynechococcus lividus], and eucaryotic algae (Chlorella pyrenoidsa, Chlorella vulgaris, Euglena gracilis, Scenedesmus obliquus, andChlamydomonas reinhardtii). Other thiols measured included cysteine, -glutamylcysteine, thiosulfate, coenzyme A, and sulfide; several unidentified thiols were also detected. Many of the organisms examined also exhibited a marked ability to reduce mBBr to syn-(methyl,methyl)bimane, an ability that was quenched by treatment with 2-pyridyl disulfide or 5,5-bisdithio-(2-nitrobenzoic acid) prior to reaction with mBBR. These observations indicate the presence of a reducing system capable of electron transfer to mBBr and reduction of reactive disulfides. The distribution of GSH in phototrophic eubacteria indicates that GSH synthesis evolved at or around the time that oxygenic photosynthesis evolved.     

Recent trends in ionic liquid (IL) tolerant enzymes and microorganisms for biomass conversion

Second generation biofuel production depends on lignocellulosic (LC) biomass transformation into simple sugars and their subsequent fermentation into alcohols. However, the main obstacle in this process is the efficient breakdown of the recalcitrant cellulose to sugar monomers. Hence, efficient feedstock pretreatment and hydrolysis are necessary to produce a cost effective biofuel. Recently, ionic liquids (ILs) have been recognized as a promising solvent able to dissolve different biomass feedstocks, providing higher sugar yields. However, most of the hydrolytic enzymes and microorganisms are inactivated, completely or partially, in the presence of even low concentrations of IL, making necessary the discovery of novel hydrolytic enzymes and fermentative microorganisms that are tolerant to ILs. In this review, the current state and the challenges of using ILs as a pretreatment of LC biomass was evaluated, underlining the advances in the discovery and identification of new IL-tolerant enzymes and microorganisms that could improve the bioprocessing of biomass to fuels and chemicals.     

Genetic influences on tissue deposition of aluminum in mice

Aluminum is a known neurotoxin and has been suggested to play a role in the development of Senile Dementia of the Alzheimer's Type. The relationship between aluminum exposure and senile dementia cannot be a simple one, however, as not all exposure results in neurotoxic manifestations. To determine if there are genetic differences in susceptibility to moderate aluminum exposure, 16 mice of five inbred strains were divided into two groups. The control group was fed a purified diet containing all known requirements for mice; the experimental group was fed the same diet supplemented with 260 mg Al/kg diet for 28 d. Analysis of brains, livers, and tibias for aluminum concentrations revealed strain differences in response to dietary treatment. The most notable results occurred in the DBA/2 and C3H/2 strains, with brain aluminum levels higher in the experimental groups. In contrast, A/J, BALB/c, and C57BL/6 strains showed no differences in brain aluminum in response to dietary treatment. These findings suggest that there are genetic differences in the permeability of the blood brain barrier and lend support to the hypothesis that variability in aluminum toxicity may be, in part, genetically determined.