General Mechanisms for Solute Transport Across the Tonoplast of Plant Vacuoles: a Patch-Clamp Survey of Ion Channels and Proton Pumps

The electrical properties of the tonoplast from a large variety of plant materials such as mesophyll cells, storage cells, tumor cells, suspension cultured cells, guard cells, coleoptile cells, and liverwort cells have been investigated using the patch-clamp technique. Whole-vacuole recordings were employed to study the dynamics of an ATP-dependent proton pump by directly measuring the electrogenic currents. The addition of Mg-ATP induced an inwardly directed current which depolarized the tonoplast (the vacuole becoming positive inside). Furthermore, voltage-dependent passive ion fluxes were analyzed using whole vacuoles and isolated membrane patches. Whole-vacuolar currents and single-channel currents were induced at hyperpolarizing potentials, whereas currents decreased at positive trans-tonoplast potentials. The electrical properties of the tonoplast of vacuoles from various plant tissues were similar and it was concluded that ion fluxes across the tonoplast follow the same general mechanisms.     

Recent Advances in Polymer Electrolytes for Zinc Ion Batteries: Mechanisms,Properties, and Perspectives

Aqueous rechargeable zinc ion batteries (ZIBs) have been deemed to be possible candidates for large‐scale energy storage due to their ecoefficiency, substantial reserve, safety, and low cost. However, the challenges inherent in aqueous electrolytes, such as water splitting reactions, water evaporation, and liquid leakage, have greatly hindered their development in energy storage. Fortunately, polymer electrolytes would be able to overcome the abovementioned challenges. Moreover, the flexible properties of polymer electrolytes can facilitate their future application in wearable electronics. Recently, increasing attention has been attracted to the polymer electrolyte‐based zinc ion batteries. However, the development of polymer electrolytes for ZIBs is still in the early stages due to numerous challenges. Therefore, substantial research effort is required to overcome the challenges of polymer electrolyte‐based ZIBs. In this review, the current progress in developing polymer electrolytes, including solid polymer electrolytes, gel polymer electrolytes, and hybrid polymer electrolytes, as well as the interactions between electrodes and polymer electrolytes for ZIBs is comprehensively reviewed, analyzed, and discussed in terms of their synthesis, characterization, and performance validation. To facilitate further research and development of polymer electrolytes for ZIBs, the relevant challenges are summarized and analyzed, and some underlying approaches to overcome these challenges are also proposed.     

Possible Molecular Mechanisms Involved in Nickel,Zinc and Selenium Hyperaccumulation in Plants

Abstract

The recent financial meltdown has muted the patent reform debate in the United States. But given that President Obama, as well as many members of Congress, support patent reform, we expect the debate to resurface. In this essay, we look carefully at reports from three prestigious organizations which have been enormously influential in the debate. We examine the empirical basis contained in these reports upon which proposed legislative changes are based. We conclude that the empirical data being used to justify the need for reform either has serious methodological limitations or is non-existent. Moreover, we review recent court decisions which have already altered the patent environment calling into further question whether the limited data that exists is still applicable. The effect of these recent decisions has not been adequately evaluated or assessed. Thus, we recommend other empirical studies are needed to inform public policy as to whether patent reform is necessary.     

植物对重金属锌耐性机理的研究进展

Zn是植物必需的营养元素,同时也是一种常见的有毒重金属元素.由于长期的环境选择和适应进化,植物相应对Zn~(2+)产生了耐性,可减轻或避免Zn~(2+)的毒害.植物对锌耐性机制有:菌根和细胞膜对Zn~(2+)吸收的阻止和控制,其中控制Zn~(2+)的细胞膜跨膜转运器主要有(ZIP)类、阳离子扩散促进器(CDF)类和B-type ATPase (HMA)类;金属硫蛋白(MTs)、植物螯合素(PCs)和有机酸等Zn~(2+)螯合物质的体内螯合解毒;体内区室化分隔以及通过抗氧化系统和渗透调节物质的代谢调节等.本文从生理和分子水平上综述了植物对Zn~(2+)耐性机理的研究进展,并在此基础上提出目前存在的问题和今后研究的重点领域,为该领域的相关研究提供资料和借鉴.     

Ca2+-Calmodulin Modulates Ion Channel Activity in Storage Protein Vacuoles of Barley Aleurone Cells

Many plant ion channels have been identified, but little is known about how these transporters are regulated. We have investigated the regulation of a slow vacuolar (SV) ion channel in the tonoplast of barley aleurone storage protein vacuoles (SPV) using the patch-clamp technique. SPV were isolated from barley aleurone protoplasts incubated with CaCl2 in the presence or absence of gibberellic acid (GA) or abscisic acid (ABA). A slowly activating, voltage-dependent ion channel was identified in the SPV membrane. Mean channel conductance was 26 pS when 100 mM KCl was on both sides of the membrane, and reversal potential measurements indicated that most of the current was carried by K+. Treatment of protoplasts with GA3 increased whole-vacuole current density compared to SPV isolated from ABA- or CaCl2-treated cells. The opening of the SV channel was sensitive to cytosolic free Ca2+ concentration ([Ca2+]i) between 600 nM and 100 [mu]M, with higher [Ca2+]i resulting in a greater probability of channel opening. SV channel activity was reduced greater than 90% by the calmodulin (CaM) inhibitors W7 and trifluoperazine, suggesting that Ca2+ activates endogenous CaM tightly associated with the membrane. Exogenous CaM partially reversed the inhibitory effects of W7 on SV channel opening. CaM also sensitized the SV channel to Ca2+. In the presence of ~3.5 [mu]M CaM, specific current increased by approximately threefold at 2.5 [mu]M Ca2+ and by more than 13-fold at 10 [mu]M Ca2+. Since [Ca2+]i and the level of CaM increase in barley aleurone cells following exposure to GA, we suggest that Ca2+ and CaM act as signal transduction elements mediating hormone-induced changes in ion channel activity.     

Integral Membrane Protein Sorting to Vacuoles in Plant Cells: Evidence for Two Pathways

Plant cells may contain two functionally distinct vacuolar compartments. Membranes of protein storage vacuoles (PSV) are marked by the presence of α-tonoplast intrinsic protein (TIP), whereas lytic vacuoles (LV) are marked by the presence of γ-TIP. Mechanisms for sorting integral membrane proteins to the different vacuoles have not been elucidated. Here we study a chimeric integral membrane reporter protein expressed in tobacco suspension culture protoplasts whose traffic was assessed biochemically by following acquisition of complex Asn-linked glycan modifications and proteolytic processing, and whose intracellular localization was determined with confocal immunofluorescence. We show that the transmembrane domain of the plant vacuolar sorting receptor BP-80 directs the reporter protein via the Golgi to the LV prevacuolar compartment, and attaching the cytoplasmic tail (CT) of γ-TIP did not alter this traffic. In contrast, the α-TIP CT prevented traffic of the reporter protein through the Golgi and caused it to be localized in organelles separate from ER and from Golgi and LV prevacuolar compartment markers. These organelles had a buoyant density consistent with vacuoles, and α-TIP protein colocalized in them with the α-TIP CT reporter protein when the two were expressed together in protoplasts. These results are consistent with two separate pathways to vacuoles for membrane proteins: a direct ER to PSV pathway, and a separate pathway via the Golgi to the LV.     

Post-Anoxia in Plants: Reasons,Consequences, and Possible Mechanisms

Russian Journal of Plant Physiology - One of the adverse factors affecting plants is oxygen deficiency, which develops as a result of excessive waterlogging and flooding. In a natural habitat,...     

Cytoplasmic pH Regulation in Acer pseudoplatanus Cells: II. Possible Mechanisms Involved in pH Regulation during Acid-Load

Qualitative and quantitative aspects of the mechanisms involved in the regulation of cytoplasmic pH during an acid-load have been studied in Acer pseudoplatanus cells. Two main processes, with about the same relative importance, account for the removal of H⁺ from the cytoplasm, namely a `metabolic consumption' of protons and the excretion of protons or proton-equivalents out of the cells. The metabolic component corresponds to a change in the equilibrium between malate synthesis and degradation leading to a 30% decrease of the malate content of the cells during the period of cytoplasmic pH regulation. Various conditions which severely inhibit the activity of the plasmalemma proton pump ATPase reduce, at most by 50%, the excretion of H⁺. This suggests that, besides the plasmalemma proton-pump, other systems are involved in the excretion of proton-equivalents. Indirect information on qualitative and quantitative features of these systems is described, which suggests the involvement of Na⁺ and HCO₃⁻ exchanges in the regulation of cytoplasmic pH of acid-loaded cells.     

根尖分生组织细胞核大小:一个可能用于植物入侵性评估的新指标(英文)

植物的入侵性与DNA C-值之间存在统计学上的负相关关系。在这种关系中,细胞和细胞核大小可能起关键作用,因此我们推测分生组织细胞核大小在评估植物或至少某些分类群的入侵性方面有潜在的应用价值。本研究以豌豆属(Vicia)5种入侵能力不同的植物为材料,观察了它们的分生组织染色体、细胞核和细胞大小以及有丝分裂速率,同时测定了种子产量、单位种子干重产生的幼苗生物量(近似于幼苗相对生长速率)和生活史的长短。结果显示根尖分生区细胞核较小的植物细胞较小,细胞分裂速率快,单位种子干重产生的幼苗生物量高,种子小而数量多,生活史短。这些结果表明5种豌豆属植物中分生组织细胞核较小的倾向于具有较高的入侵性,其原因主要是:(1)能够产生小而多的种子;(2)具有较高的有丝分裂速率、相对较快的幼苗生长速率和短的生活史。分生组织细胞核大小影响植物入侵性与DNA C-值的作用是一致的,在植物入侵性评估模型中,分生组织细胞核大小在评估植物入侵性方面可能具有潜在的应用价值,而且其测定方便、费用低廉。但是,这一指标的应用范围和条件需要进一步筛选。     

Ionic Balance during Malic Acid Accumulation in Vacuoles of a CAM Plant, Graptopetalum paraguayense

We studied the ionic balance during diurnal changes in the levelsof accumulated malic acid and hydrogen ion in the vacuoles ofGraptopetalum paraguayense, a crassulacean acid metabolism (CAM)plant. There was a clear diurnal rhythm of the pH and the totalmalic acid content, but the amount of negative charges due tothe unprotonated carboxyl groups of malic acid remained approximatelyconstant. The negative charges were balanced by the positivecharges of cations, which were also constant throughout thediurnal CAM rhythm. The results gave evidence for the electroneutralityof the translocation of the malic acid and protons across thetonoplast membrane. (Received July 30, 1987; Accepted March 17, 1988)     

Regulation of Vacuolar pH of Plant Cells: I. Isolation and Properties of Vacuoles Suitable for P NMR Studies

For the first time, the ³¹P nuclear magnetic resonance technique has been used to study the properties of isolated vacuoles of plant cells, namely the vacuolar pH and the inorganic phosphate content. Catharanthus roseus cells incubated for 15 hours on a culture medium enriched with 10 millimolar inorganic phosphate accumulated large amounts of inorganic phosphate in their vacuoles. Vacuolar phosphate ions were largely retained in the vacuoles when protoplasts were prepared from the cells and vacuoles isolated from the protoplasts. Vacuolar inorganic phosphate concentrations up to 150 millimolar were routinely obtained. Suspensions prepared with 2 to 3 × 10⁶ vacuoles per milliliter from the enriched C. roseus cells have an internal pH value of 5.50 ± 0.06 and a mean trans-tonoplast ΔpH of 1.56 ± 0.07. Reliable determinations of vacuolar and external pH could be made by using accumulation times as low as 2 minutes. These conditions are suitable to follow the kinetics of H⁺ exchanges at the tonoplast. The ³¹P nuclear magnetic resonance technique also offered the possibility of monitoring simultaneously the stability of the trans-tonoplast pH and phosphate gradients. Both appeared to be reasonably stable over several hours. The buffering capacity of the vacuolar sap around pH 5.5 has been estimated by several procedures to be 36 ± 2 microequivalents per milliliter per pH unit. The increase of the buffering capacity due to the accumulation of phosphate in the vacuoles is, in large part, compensated by a decrease of the intravacuolar malate content.     

Glutathione in Intact Vacuoles: Comparison of Glutathione Pools in Isolated Vacuoles,Plastids, and Mitochondria from Roots of Red Beet

Proportions between oxidized and reduced glutathione forms were determined in vacuoles isolated from red beet (Beta vulgaris L.) taproots. The pool of vacuolar glutathione was compared with glutathione pools in isolated plastids and mitochondria. The ratio of glutathione forms was assessed by approved methods, such as fluorescence microscopy with the fluorescent probe monochlorobimane (MCB), high-performance liquid chromatography (HPLC), and spectrophotometry with 5,5′-dithiobis-2-nitrobenzoic acid (DTNB). The fluorescence microscopy revealed comparatively low concentrations of reduced glutathione (GSH) in vacuoles. The GSH content was 104 μM on average, which was lower than the GSH levels in mitochondria (448 μM) and plastids (379 μM). The content of reduced (GSH) and oxidized (GSSG) glutathione forms was quantified by means of HPLC and spectrophotometric assays with DTNB. The glutathione concentrations determined by HPLC in the vacuoles were 182 nmol GSH and 25 nmol GSSG per milligram protein. The respective concentrations of GSH and GSSG in the plastids were 112 and 6 nmol/mg protein and they were 228 and 10 nmol/mg protein in the mitochondria. The levels of GSH determined with DTNB were 1.5 times lower, whereas the amounts of GSSG were, by contrast, 1.5–2 times higher than in the HPLC assays. Although the glutathione redox ratios depended to some extent on the method used, the GSH/GSSG ratios were always lower for vacuoles than for plastids and mitochondria. In vacuoles, the pool of oxidized glutathione was higher than in other organelles.     

Effects of Clonidine Withdrawal: Possible Mechanisms and Suggestions for Management

A severe rebound rise in blood pressure with agitation and insomnia had been noted in five patients when they had previously ceased clonidine (Catapres) This has been shown to be reproducible in these patients and to be associated with a significant increase in urinary catecholamine excretion. The blood pressure can be controlled and the symptoms alleviated promptly by alpha and beta adrenergic receptor blockade using intravenous phentolamine and propranolol.     

Studies on Feeding and Digestion in Protozoa. III. Acid Phosphatase Activity in Food Vacuoles of Paramecium multimicronucleatum

SYNOPSIS. Acid phosphatase activity was studied in total mounts and sections of agnotobiotic Paramecium multimicronucleatum by the alpha-naphthyl phosphate-hexazotized rosanilin method. Timing was achieved by India ink marking of food vacuoles. Enzyme activity is present in small endoplasmic granules and in the greatest part of food vacuoles. Following an inactive stage (stage I) of an average length of 5 min the activity appears at the periphery of the vacuole, in most cases in the form of granules (stage II). A high activity level (stage III) is attained within 1 1/2 min and maintained for the most part of the vacuolar cycle. The activity disappears only in the latest vacuoles before egestion (stage IV). The appearance of activity is not concurrent with but succeeding to the maximum of vacuolar acidity as ascertained by feeding Congo red stained killed yeast cells. On the basis of these results the food vacuoles may be looked upon as belonging to the lysosomes sensu lato.     

Evaluation of Different Amendments to Stabilize Cadmium,Zinc, and Copper in a Contaminated Soil: Influence on Metal Leaching and Phytoavailability

The contamination of soils with heavy metals is a global disaster that is related to human activities. Phytostabilization basically refers to the use of metal-tolerant plants and inexpensive mineral or organic soil amendments to reduce the concentrations or toxic effects of contaminants in the environment. Here, we tested the effects of four cost-effective amendments (CaCO₃, phosphate rock, activated carbon, and exhausted olive cake ash) on Cd, Zn, and Cu leaching and uptake by ryegrass (Lolium perenne L.). The results showed that all amendments reduced Cd, Zn, and Cu leaching, mainly due to the alkalinity increase. Among all amendments tested, CaCO₃ was the most effective treatment in decreasing both the heavy-metal leaching and concentrations in ryegrass shoots. Results obtained suggest the efficacy of several amendments, but further work is needed to gain insight into their possible synergetic effects.     

Molecular Mechanisms of Hormonal Activity. II. Kinase Systems. Systems with Intracellular Receptors. Transactivation of STS

Hormone receptors and other components, functional mechanisms, and biological role of analyzed signal transduction systems (STS) are described. The recently revealed module principle of the structure and STS transactivation providing diversity and plasticity of regulation are highlighted. STS activities are significantly changed in many diseases. Novel promising pharmaceuticals targeted to certain components of STS increase in number from year to year. The data published by the beginning of January 2004 are summarized in this review.__________Translated from Biokhimiya, Vol. 70, No. 4, 2005, pp. 476–492.Original Russian Text Copyright © 2005 by Kulinsky, Kolesnichenko.Part I of this review, Molecular Mechanisms of Hormonal Activity. I. Receptors. Neuromediators. Systems with Second Messengers, was published in Biochemistry (Moscow), Vol. 70, No. 1.