Phytochelatin synthesis plays a similar role in shoots of the cadmium hyperaccumulator Sedum alfredii as in non‐resistant plants

Phytochelatin (PC) synthesis is considered necessary for Cd tolerance in non‐resistant plants, but roles for PCs in hyper‐accumulating species are currently unknown. In the present study, the relationship between PC synthesis and Cd accumulation was investigated in the Cd hyperaccumulator Sedum alfredii Hance. PCs were most abundant in leaves followed by stems, but hardly detected by the reversed‐phase high‐performance liquid chromatography (HPLC) in roots. Both PC synthesis and Cd accumulation were time‐dependent and a linear correlation between the two was established with about 1:15 PCs : Cd stoichiometry in leaves. PCs were found in the elution fractions, which were responsible for Cd peaks in the anion exchange chromatograph assay. About 5% of the total Cd was detected in these elution fractions as PCs were found. Most Cd was observed in the cell wall and intercellular space of leaf vascular cells. These results suggest that PCs do not detoxify Cd in roots of S. alfredii. However, like in non‐resistant plants, PCs might act as the major intracellular Cd detoxification mechanism in shoots of S. alfredii.     

水稻幼苗根细胞质膜和液泡膜微囊Ca2+-ATP酶的特性

水稻幼苗根质膜和液泡膜Ca2 -ATP酶对ATP的Km值分别为7.1和4.5 μ mol·L-1;反应的最适pH分别为8.0和7.0.两者活性均受Na3VO4和曙红B(EB)抑制;CPZ抑制质膜Ca2 -ATP酶活性,但促进液泡膜Ca2 -ATP酶活性.30mmol·L-1CaCl2浸种和CaCl2浸种结合低温锻炼预处理,均可提高此酶的活性和冷稳定性.     

植物水通道蛋白及其活性调节

水通道蛋白是对水专一的通道蛋白,普遍存在于动、植物及微生物中。研究表明高等植物的质膜和液泡膜上存在着丰富的水通道蛋白,其种类繁多,分布广泛,并具有一定的组织特异性。植物水通道蛋白的活性受到严格的调控,其调节方式主要有两种,分别为基因水平的表达调控和翻译后的修饰作用。     

The hexose transporters at the plasma membrane and the tonoplast of higher plants

The uptake of hexoses in higher plant cells is thought to be catalyzed by an H⁺/hexose contrasporter in the plasma membrane. Transport studies with isolated plant vacuoles indicate that, at the tonoplast, a second hexose transporter is located with properties different from the plasma membrane transporter. Recently membrane vesicles of high purity and defined orientation have been used for a more rigorous individual characterization of these two carriers. Concomitantly, a cDNA for the inducible H⁺/hexose cotransporter of the green alga Chlorella has been sequenced and shown to exhibit homology to a group of hexose transporters (for facilitated diffusion) of other eukaryotic and prokaryotic organisms. With a probe derived from the Chlorella sequence, the first plant gene for an H⁺/hexose contransporter ( Arabidopsis thaliana ) has been isolated, opening the route to molecular studies of structure, function and evolution of the hexose transporters of higher plants. The present review discusses recent work on the kinetic characterization and identification of the higher plant plasma membrane and tonoplast hexose transporters as well as their respective cellular functions. Furthermore, perspectives for future research on the plant hexose transporters are outlined.     

Meloidogyne incognita-Induced Changes in Cell Permeability of Galled Roots

Electrolyte leakage of Meloidogyne incognita-infected and healthy tomato roots was compared by conductivity measurements, and by compartmental analysis using ⁸⁶Rb. Conductivity measurements suggested difference in electrolyte loss from healthy and galled roots. On a percentage basis, a greater rate of efflux occurred for healthy plants, but galled roots contain more electrolytes and may show a larger net loss. Compartmental analysis indicated that: (i) the longer half-time for ⁸⁶Rb loss from vacuoles of galled root cells could indicate either a greater vacuolar content or decreased tonoplast permeability, (ii) the shorter half-time for loss ⁸⁶Rb from the cytoplasm of galled root cells could reflect either a reduced cytoplasmic content or an increased plasma membrane permeability, and (iii) in split-root plants, the permeability of the tonoplast and the plasma membrane of cells in nongalled roots is increased by nematode infection on the other half of the root system. Thus, a mechanism for mobilizing minerals to the infection site is proposed.     

盐胁迫对大麦幼苗质膜,液泡膜上共价和非共价结合多胺含量的影响

用不同浓度ＮａＣｌ处理７ｄ龄大麦（Ｈｏｒｄｅｕｍ ｖｕｌｇａｒｅＬ．）幼苗３ｄ。以非共价键和共价键形式分别与质膜和液泡膜微囊及膜蛋白结合的多胺含量受低 度盐的促进而被高浓度盐所抑制。以非共价键形式与膜微囊结合的各种多胺中亚精胺（Ｓｐｄ）含量最高,占膜上多胺总量的４０％－７０％,与膜蛋白共价结合的各种多胺中腐胺（Ｐｕｔ）含量占主导地位,占膜蛋白上多胺总量的３５％－６０％。在根系液泡膜上发现一种含量丰     

Centaurin-like protein Cnt5 contributes to arsenic and cadmium resistance in fission yeast

Arsenic (As) and cadmium (Cd) are two of the most hazardous substances in the environment and have been implicated in a number of human diseases including cancer. Their mechanisms of toxicity and subsequent carcinogenesis are not understood. To identify the genes involved in As/Cd detoxification, we screened a random insertional mutagenesis library of Schizosaccharomyces pombe for mutants that are hypersensitive to As/Cd. Mutations were mapped to spc1 ⁺ ( sty1 ⁺) and SPBC17G9.08c . Spc1 is a stress-activated protein kinase orthologous to human p38. A fragment of SPBC17G9.08c was previously identified as csx2 , a high-copy suppressor of cut6 that encodes an acetyl-CoA carboxylase involved in fatty acid biosynthesis. SPBC17G9.08c is a member of the centaurin ADP ribosylation factor GTPase activating protein family found in a variety of fungi, plants and metazoans, but not in Saccharomyces cerevisiae . Cnt5, so named because its closest human homolog is centaurin β-5, binds to phosphatidic acid and phosphatidyl serine in vitro . Microscopic localization of Cnt5-GFP indicates significant redistribution of Cnt5 from the cytoplasm to the cell membranes in response to As stress. These data suggest a model in which Cnt5 contributes to As/Cd resistance by maintaining membrane integrity or by modulating membrane trafficking.     

Enhanced K+-stimulated pyrophosphatase activity in NaCl-adapted cells of Acer pseudoplatanus

Cell suspension cultures of Acer pseudoplatanus L. (Bligny cell line) adapted to growth in the presence of NaCl, are a useful tool for investigating mechanisms for cellular salt tolerance. We compared the activities of vanadate-sensitive (plasma membrane) and nitrate-sensitive (tonoplast) ATPases, and tonoplast K⁺-stimulated PPase in microsomal fractions (8000–108 000 g) from unadapted and NaCl-adapted (80 m M ) cells of A. pseudoplatanus . Since NaCl reduces the growth rate of the culture, the two cell lines were harvested and compared at both the same cellular density and at the same growth phase (middle exponential phase or beginning of the stationary phase). The ATPase activity of the plasma membrane (expressed both on the basis of protoplast number and in relation to protein content) was not affected by the adaptation to salinity. The two enzyme activities of the tonoplast (mainly as expressed on a protein basis) were higher in adapted than in unadapted cells. However, a preferential increase in PPase activity took place, although the pH dependence, ionic requirements, and apparent K_m of the PPase activity were the same in the two cell lines. The three enzyme activities showed different sensitivities to detergents such as Triton X-100, Brij 58 and lysophosphatidylcholine (LPC). The stimulation of K⁺-stimulated PPase activity by detergents was higher in adapted than in unadapted cells. This suggests that the salt-induced enhancement of the PPase activity might partially depend on a modification of the lipid component of the tonoplast.     

质膜钙离子ATP酶

钙离子(Ca2+)是重要的第二信使,通过与效应蛋白的结合和解离,以及在不同细胞器之间的穿梭运动而精确调控细胞活动,参与多种重要生命过程。细胞内具有精确调节Ca2+时空分布的调控系统。在静息状态下,细胞内的游离Ca2+浓度约为100 nmol/L;而当细胞受到信号刺激后,胞内的Ca2+浓度可上升至1000 nmol/L甚至更高。细胞中存在多种跨膜运送Ca2+的膜蛋白,以精确调节Ca2+浓度的时空动态变化,其中,细胞质膜上的多种Ca2+通道(包括电压门控通道、受体门控通道、储存控制通道等),以及内质网/肌质网和线粒体等胞内"钙库"膜上的雷诺丁受体、三磷酸肌醇受体等膜蛋白复合物,均可提升胞内Ca2+浓度,而细胞质膜上的钠钙交换体、质膜Ca2+-ATP酶、"钙库"膜上的内质网Ca2+-ATP酶、线粒体Ca2+单向转运体等,可将Ca2+浓度降低至静息态水平。质膜钙ATP酶是向细胞外运送Ca2+的关键膜蛋白,本文将对其结构、功能及其酶活性的调控机制做一简要综述。     

Identification and characterization of Cr-, Cd-, and Ni-tolerant bacteria isolated from mine tailings

Eleven bacterial strains were isolated from soil samples collected from mine tailings. Bacterial strains were checked for tolerance against heavy metals (Cr, Cd, Ni), using the agar dilution method. All the strains showed multiple tolerances against heavy metals, but the most promising results appeared in strains BCr3, BCd33, and BNi11: they were tolerant to 15 mM of Cr⁶⁺, 7.5 mM of Cd²⁺, and 10 mM of Ni²⁺, respectively. The effect of heavy metals on bacterial growth was tested together with their ability to grow in different pH, NaCl, and temperature values. Bacterial isolates grew well between pH 7.5 and 8.5. The optimum temperature for maximum growth was between 35 and 37°C, and no significant change in bacterial growth was observed in the presence of 2% NaCl. In addition, the bioaccumulation potential of bacterial strains was investigated. Bacterial strains BCr3, BCd33, and BNi11 showed high bioaccumulation ability of Cr (68.7%), Cd (72.4%), and Ni (69.8%), respectively. All bacterial isolates were identified by 16S rRNA gene sequencing. Analysis of plasmid content revealed that all bacterial isolates contained a single plasmid. Further, polymerase chain reaction together with DNA sequence analysis was used to screen all bacterial strains for the presence metal tolerance genes (czcD, chrA, chrB, czcB, czcC, nccA, and cadA) on both plasmid and chromosomal genomes.