Subcellular localization of chromium and nickel in root cells of Allium cepa by EELS and ESI

The significance of ion-exchange properties of plant root cell walls for nutrient and water uptake by plants

This review examines the key aspects of ion exchange and diffusion in plant root cell walls and the implications of these processes for the uptake of mineral nutrients and water under both normal and adverse environmental conditions. The data available to date shows that the ion-exchange properties of plant root cell walls are influenced by the plant age and growth conditions, and also vary between species. The cell wall volume and its ability to swell, which regulate the hydraulic conductivity of the cell wall, are determined by the pH and ionic strength of the external solution. It is concluded that the analysis of physico-chemical properties of plant cell wall is an important step in the understanding of the complex processes of water and nutrient uptake.

Effects of biochar and foliar application of selenium on the uptake and subcellular distribution of chromium in Ipomoea aquatica in chromium-polluted soils

The potential toxicity of Cr to plants poses a severe threat to human health. Biochar and Se can reduce the absorption of Cr and its phytotoxicity in plants, but the associated mechanisms at subcellular levels have not been addressed in depth. A study was designed to investigate the effects of biochar, foliar application of Se, and their combination on the physicochemical and biological properties of the soil, Cr availability, Cr absorption, and Cr subcellular distribution in each part of the plant, and biomass and quality of two water spinach (Ipomoea aquatica) genotypes. The results showed that biochar, Se, and their combination increased the organic matter content and available NPK nutrients in the soil and improved the urease, phosphatase, catalase, and sucrase activities in the soil. Furthermore, they also increased the number of bacteria, actinomycetes, and fungi in the soil, were conducive to dry matter accumulation in I. aquatica, and increased the contents of soluble sugar and soluble protein in its leaves. The Cr contents in the roots and shoots of I. aquatica under different treatments were reduced compared with those in the control group. The content of Cr(VI) in the root-soil of I. aquatica with low Cr accumulation and the contents of Cr in various parts of I. aquatica were lower than those in I. aquatica with high Cr accumulation, and the absorbed Cr was mainly accumulated in the roots. Cr was mainly distributed in the cell walls and soluble fractions of the roots, stems, and leaves of I. aquatica and was less distributed in the organelles. Biochar and Se helped to increase the proportion of Cr in the cell walls of the roots and soluble fractions of the leaves of I. aquatica. The effects of improving the soil properties, passivating and inhibiting Cr absorption by I. aquatica, and reducing the Cr proportion in the organelles of biochar were superior to those of Se application. The foliar application of Se and biochar had no synergistic effect on inhibiting Cr absorption by I. aquatica. Based on these findings, the application of biochar in Cr-contaminated soil or foliar application of Se with low Cr-accumulating plants may be effective means of reducing the Cr absorption by plants and its toxicity to ensure the safe production of agricultural products in Cr-contaminated regions.

How Plants Handle Trivalent (+3) Elements

Plant development and fitness largely depend on the adequate availability of mineral elements in the soil. Most essential nutrients are available and can be membrane transported either as mono or divalent cations or as mono- or divalent anions. Trivalent cations are highly toxic to membranes, and plants have evolved different mechanisms to handle +3 elements in a safe way. The essential functional role of a few metal ions, with the possibility to gain a trivalent state, mainly resides in the ion's redox activity; examples are iron (Fe) and manganese. Among the required nutrients, the only element with +3 as a unique oxidation state is the non-metal, boron. However, plants also can take up non-essential trivalent elements that occur in biologically relevant concentrations in soils. Examples are, among others, aluminum (Al), chromium (Cr), arsenic (As), and antimony (Sb). Plants have evolved different mechanisms to take up and tolerate these potentially toxic elements. This review considers recent studies describing the transporters, and specific and unspecific channels in different cell compartments and tissues, thereby providing a global vision of trivalent element homeostasis in plants.

Selenium alleviated chromium stress in Chinese cabbage (Brassica campestris L. ssp. Pekinensis) by regulating root morphology and metal element uptake

Excessive chromium (Cr) causes toxicity to plants, while the beneficial effects of selenium (Se) have been verified in plants under various adverse conditions. Under Cr stress, the impacts of exogenous Se on root morphology and metal element uptake were investigated in root of Chinese cabbage by cellular and biochemical approaches. Exogenous Se alleviated Cr-induced irreversible damage to root morphology, plasma membrane integrity and ultrastructure of root tip cells. Compared with Cr treatment alone, exogenous Se reduced root Cr content by 17%. Se supply changed the subcellular distribution of Cr in root, and the concentration of Cr was reduced in the fractions of plastids and mitochondria, while increased in soluble fraction. Besides, exogenous Se counteracted the nutrient elements (Na, Ca, Fe, Mn, Cu and Zn) loss induced by Cr. For plant with Se pretreatment, the increase rate of Cr influx was lower than that of plant without Se pretreatment, particularly in solution containing high concentration (100-400 μmol L^-1) of Cr. In addition, higher K_m value was observed in plant with Se pretreatment, which indicated a lower Cr affinity than that of plant without Se pretreatment. The results suggest that Se modified root morphology and regulated nutrient elements uptake by root, which might play a combined role in reducing Cr uptake by root, consequently alleviating Cr stress and maintaining plant growth.

The role of the cell walls in Ni binding by plant roots

The role of the cell wall in short-term Ni uptake at different solution Ni levels was investigated in mung bean (Vigna radiata (L.) R. Wilczek) and wheat (Triticum aestivum L., cv. Inna). Both Ni-binding capacity of the CWs and roots are lower for wheat than for mung bean at all Ni levels in the solution. For both plants amounts of Ni associated with roots and root cell walls increased with Ni concentration. The contribution of CWs to Ni absorption by roots depends on Ni level in the medium and plant species. The Ni accumulated in CWs could account for total Ni content of roots (except for wheat in highest Ni treatment). Besides, mung bean plants employ the strategy of reducing Ni accumulation in the root CWs during exposure to excess but not toxic solution Ni level. According to the results, predominant Ni binding in the apoplast of mung bean and wheat roots is observed at both high and low external Ni, which suggests that apoplastic pathway is the main means of Ni transport in the root cortex of these species.

Chromium tolerance, bioaccumulation and localization in plants: An overview

In the current industrial scenario, chromium (Cr) as a metal is of great importance, but poses a major threat to the environment. Phytoremediation provides an environmentally sustainable, ecofriendly, cost effective approach for environmental cleanup of Cr. This review presents the current status of phytoremediation research with particular emphasis on cleanup of Cr contaminated soil and water systems. It gives a detailed account of the work done by different authors on the Cr bioavailability, uptake pathway, toxicity and storage in plants following the phytoextraction mechanism. This paper also describes recent findings related to Cr localization in hyperaccumulator plants. It gives an insight into the processes and mechanisms that allow plants to remove Cr from contaminated sites under varying conditions. These detailed knowledge of changes in plant metabolic pool in response to Cr stress would immensely help understand and improve the phytoextraction process. Further, this review provides a detailed understanding of Cr uptake and detoxification mechanism by plants that can be applied in developing a suitable approach for a better applicability of the process.

Vacuolar compartmentalization as indispensable component of heavy metal detoxification in plants

Plant cells orchestrate an array of molecular mechanisms for maintaining plasmatic concentrations of essential heavy metal (HM) ions, for example, iron, zinc and copper, within the optimal functional range. In parallel, concentrations of non-essential HMs and metalloids, for example, cadmium, mercury and arsenic, should be kept below their toxicity threshold levels. Vacuolar compartmentalization is central to HM homeostasis. It depends on two vacuolar pumps (V-ATPase and V-PPase) and a set of tonoplast transporters, which are directly driven by proton motive force, and primary ATP-dependent pumps. While HM non-hyperaccumulator plants largely sequester toxic HMs in root vacuoles, HM hyperaccumulators usually sequester them in leaf cell vacuoles following efficient long-distance translocation. The distinct strategies evolved as a consequence of organ-specific differences particularly in vacuolar transporters and in addition to distinct features in long-distance transport. Recent molecular and functional characterization of tonoplast HM transporters has advanced our understanding of their contribution to HM homeostasis, tolerance and hyperaccumulation. Another important part of the dynamic vacuolar sequestration syndrome involves enhanced vacuolation. It involves vesicular trafficking in HM detoxification. The present review provides an updated account of molecular aspects that contribute to the vacuolar compartmentalization of HMs.

Carotenoids and Antioxidant Enzymes as Biomarkers of the Impact of Heavy Metals in food Chain

Antioxidant enzymes (catalase and peroxidase) and carotenoids lutein and β-carotene are often used as biomarkers of metal contamination of water and agricultural soils. In this study, the effects of heavy metals present in irrigation water on the aforementioned carotenoids of potatoes Solanum tuberosum L. and carrots Daucus carota L., cultivated in a greenhouse and irrigated with a water solution including different levels of Cr(VI) and Ni(II) were investigated. These results were compared to the levels of the same metabolites that had been assessed in market-available potato and carrot samples. The findings indicated that the levels of the examined metabolites on the treated with Cr and Ni samples, resemble the levels of the same parameters in the market samples, originating from polluted areas. Therefore, the antioxidant enzymes, catalase and peroxidase, and the carotenoids, lutein and β-carotene, could be handled as indicators of heavy metal pollution.

Subcellular Sequestration and Impact of Heavy Metals on the Ultrastructure and Physiology of the Multicellular Freshwater Alga Desmidium swartzii

Due to modern life with increasing traffic, industrial production and agricultural practices, high amounts of heavy metals enter ecosystems and pollute soil and water. As a result, metals can be accumulated in plants and particularly in algae inhabiting peat bogs of low pH and high air humidity. In the present study, we investigated the impact and intracellular targets of aluminum, copper, cadmium, chromium VI and zinc on the filamentous green alga Desmidium swartzii, which is an important biomass producer in acid peat bogs. By means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) it is shown that all metals examined are taken up into Desmidium readily, where they are sequestered in cell walls and/or intracellular compartments. They cause effects on cell ultrastructure to different degrees and additionally disturb photosynthetic activity and biomass production. Our study shows a clear correlation between toxicity of a metal and the ability of the algae to compartmentalize it intracellularly. Cadmium and chromium, which are not compartmentalized, exert the most toxic effects. In addition, this study shows that the filamentous alga Desmidium reacts more sensitively to aluminum and zinc when compared to its unicellular relative Micrasterias, indicating a severe threat to the ecosystem.

An in ovo investigation into the hepatotoxicity of cadmium and chromium evaluated with light- and transmission electron microscopy and electron energy-loss spectroscopy

Excessive agriculture, transport and mining often lead to the contamination of valuable water resources. Communities using this water for drinking, washing, bathing and the irrigation of crops are continuously being exposed to these heavy metals. The most vulnerable is the developing fetus. Cadmium (Cd) and chrome (Cr) were identified as two of the most prevalent heavy metal water contaminants in South Africa. In this study, chicken embryos at the stage of early organogenesis were exposed to a single dosage of 0.430 μM physiological dosage (PD) and 430 μM (×1000 PD) CdCl2, as well as 0.476 μM (PD) and 746 μM (×1000 PD) K2Cr2O7. At day 14, when all organ systems were completely developed, the embryos were terminated and the effect of these metals on liver tissue and cellular morphology was determined with light- and transmission electron microscopy (TEM). The intracellular localization of these metals was determined using electron energy-loss spectroscopy (EELS). With light microscopy, the PD of both Cd and Cr had no effect on liver tissue or cellular morphology. At ×1000 PD both Cd and Cr caused sinusoid dilation and tissue necrosis. With TEM analysis, Cd exposed hepatocytes presented with irregular chromatin condensation, ruptured cellular membranes and damaged or absent organelles. In contrast Cr caused only slight mitochondrial damage. EELS revealed the bio-accumulation of Cd and Cr along the cristae of the mitochondria and chromatin of the nuclei.

Role of Bacillus licheniformis in phytoremediation of nickel contaminated soil cultivated with rice

Heavy metal contamination in soil is an important environmental problem and it has negative effect on agriculture. Bacteria play a major role in phytoremediation of heavy metals contaminated soil. In this study, the effect of Bacillus licheniformis NCCP-59, a halophilic bacterium isolated from salt mines near Karak, Pakistan, were determined on a three week old greenhouse grown seedling and germinating seeds of two rice varieties (Basmati-385 (B-385) and KSK-282) in soil contaminated with different concentrations (0, 100, 250, 500, and 1000 ppm) of Nickel. Nickel significantly reduced the germination rate and germination percentage mainly at 500 and 1000 ppm. Significant decrease in ion contents (Na, K, and Ca) was observed while Ni ion concentration in the plant tissues increases as the concentration of Ni applied increases. The photosynthetic pigments (chlorophyll a (chl a), chlorophyll b (chl b), and carotenoids) were also decreased by the application of different concentrations of Ni. Total protein and organic nitrogen were found to be reduced at higher concentrations of Nickel. Inoculation of Bacillus licheniformis NCCP-59 improved seed germination and biochemical attribute of the plant under Ni stress. It is clear from the results that the Bacillus Licheniformis NCCP-59 strain has the ability to protect the plants from the toxic effects of nickel and can be used for the phytoremediation of Ni contaminated soil.

Bioadsorption and bioaccumulation of chromium trivalent in Cr(III)-tolerant microalgae: a mechanisms for chromium resistance

Anthropogenic activity constantly releases heavy metals into the environment. The heavy metal chromium has a wide industrial use and exists in two stable oxidation states: trivalent and hexavalent. While hexavalent chromium uptake in plant cells has been reported that an active process by carrying essential anions, the cation Cr(III) appears to be taken up inactively. Dictyosphaerium chlorelloides (Dc1M), an unicellular green alga is a well-studied cell biological model organism. The present study was carried out to investigate the toxic effect of chromium exposures on wild-type Cr(III)-sensitive (Dc1M(wt)) and Cr(III)-tolerant (Dc1M(Cr(III)R30)) strains of these green algae, and to determine the potential mechanism of chromium resistance. Using cell growth as endpoint to determine Cr(III)-sensitivity, the IC₅₀(₇₂) values obtained show significant differences of sensitivity between wild type and Cr(III)-tolerant cells. Scanning electron microscopy (SEM) showed significant morphological differences between both strains, such as decrease in cell size or reducing the coefficient of form; and transmission electron microscopy (TEM) revealed ultrastructural changes such as increased vacuolization and cell wall thickening in the Cr(III)-tolerant strain with respect to the wild-type strain. Energy dispersive X-ray analysis (SEM/XEDS) revealed that Cr(III)-tolerant D. chlorelloides cells are able to accumulate considerable amounts of chromium distributed in cell wall (bioadsorption) as well as in cytoplasm, vacuoles, and chloroplast (bio-accumulation). Morphological changes of Cr(III)-tolerant D. chlorelloides cells and the presence of these electron-dense bodies in their cell structures can be understood as a Cr(III) detoxification mechanism.

Intracellular chromium localization and cell physiological response in the unicellular alga Micrasterias

Various contaminants like metals and heavy metals are constantly released into the environment by anthropogenic activities. The heavy metal chromium has a wide industrial use and exists in two stable oxidation states: trivalent and hexavalent. Chromium can cause harm to cell metabolism and development, when it is taken up by plants instead of necessary micronutrients such as for example iron. The uptake of Cr VI into plant cells has been reported to be an active process via carriers of essential anions, while the cation Cr III seems to be taken up inactively. Micrasterias denticulata, an unicellular green alga of the family Desmidiaceae is a well-studied cell biological model organism. Cr III and VI had inhibiting effects on its cell development, while cell division rates were only impaired by Cr VI. Transmission electron microscopy (TEM) revealed ultrastructural changes such as increased vacuolization, condensed cytoplasm and dark precipitations in the cell wall after 3 weeks of Cr VI treatment. Electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) were applied to measure intracellular chromium distribution. Chromium was only detected after 3 weeks of 10 μM Cr VI treatment in electron dense precipitations found in bag-like structures along the inner side of the cell walls together with iron and elevated levels of oxygen, pointing toward an accumulation respectively extrusion of chromium in form of an iron-oxygen compound. Atomic emission spectroscopy (EMS) revealed that Micrasterias cells are able to accumulate considerable amounts of chromium and iron. During chromium treatment the Cr:Fe ratio shifted in favor of chromium, which implied that chromium may be taken up instead of iron. Significant and rapid increase of ROS production within the first 5 min of treatment confirms an active Cr VI uptake. SOD and CAT activity after Cr VI treatment did not show a response, while the glutathione pool determined by immuno-TEM decreased significantly in chromium treated cells, showing that glutathione is playing a major role in intracellular ROS and chromium detoxification.

Ultrastructure and subcellular distribution of Cr in Iris pseudacorus L. using TEM and X-ray microanalysis

Chromium pollution of freshwater is hazardous for humans and other organisms, and places a limitation on the use of polluted water sources. Phytoremediation, the use of plants to remove pollutants from the environment, is a cost-effective, environmentally friendly approach for water decontamination. To improve the efficiency of the process, it is essential to increase the current knowledge about Cr accumulation in macrophytes. Plants of Iris pseudacorus L. were treated with Cr(III) at 0.75 mM for 5 weeks to investigate Cr localization by means of transmission electron microscopy and energy dispersive X-ray analysis. Chromium induced severe ultrastructural alterations in the rhizodermis (cell wall disorganisation, thickening, plasmolysis, and electron-dense inclusions) and rhizome parenchyma (reduced cell size, cell wall detachment, vacuolation, and opaque granules). The highest Cr contents were found in the cell walls of the cortex in the roots and in the cytoplasm and intercellular spaces of the rhizome. The Cr concentration in root tissues was in the order cortex>rhizodermis>stele, whereas in the rhizome, Cr was evenly distributed. It is proposed that root and rhizome have distinct functions in the response of I. pseudacorus to Cr. The rhizodermis limits Cr uptake by means of Si deposition and cell wall thickening. The rhizome cortex generates vacuoles and granules where Cr co-occurs with S, indicating Cr sequestration by metal-binding proteins.

INTRACELLULAR METAL COMPARTMENTALIZATION IN THE GREEN ALGAL MODEL SYSTEM MICRASTERIAS DENTICULATA (STREPTOPHYTA) MEASURED BY TRANSMISSION ELECTRON MICROSCOPY-COUPLED ELECTRON ENERGY LOSS SPECTROSCOPY1

Entry of metals in form of aerosols into areas of high air humidity such as peat bogs represents a serious danger for inhabiting organisms such as the unicellular desmid Micrasterias denticulata Bréb. ex Ralfs (Desmidiaceae, Zynematophyceae, Streptophyta). To understand cellular detoxification and tolerance mechanisms, detailed intracellular localization of metal pollutants is required. This study localizes the metals aluminum (Al), zinc (Zn), copper (Cu), and cadmium (Cd) in the green algal model system Micrasterias after experimental exposure to sulfate solutions by highly sensitive TEM-coupled electron energy loss spectroscopy (EELS). Concentrations of the metals shown to induce inhibiting effects on cell development and cytomorphogenesis were chosen for these experiments. Long-term exposure to these metal concentrations led to a pronounced impact on cell physiology expressed by a general decrease in apparent photosynthesis. After long-term treatment, Zn, Al, and Cu were detected in the cell walls by EELS. Zn was additionally found in vacuoles and mucilage vesicles, and Cu in starch grains and also in mucilage vesicles. Elevated amounts of oxygen in areas where Zn, Al, and Cu were localized suggest sequestration of these metals as oxides. The study demonstrated that Micrasterias can cope differently with metal pollutants. In low doses and during a limited time period, the cells were able to compartmentalize Cu the best, followed by Zn and Al. Cu and Zn were taken up into intracellular compartments, whereas Al was only bound to the cell wall. Cd was not compartmentalized at all, which explains its strongest impact on growth, cell division rate, and photosynthesis in Micrasterias.

Compartmentalization and ultrastructural alterations induced by chromium in aquatic macrophytes

The aim of the present study was to identify the sites of accumulation of Cr in the species of macrophytes that are abundant in the Cachoeira river, namely, Alternanthera philoxeroides, Borreria scabiosoides, Polygonum ferrugineum and Eichhornia crassipes. Plants were grown in nutritive solution supplemented with 0.25 and 50 mg l(-1) of CrCl(3)·6H(2)O. Samples of plant tissues were digested with HNO(3)/HCl in a closed-vessel microwave system and the concentrations of Cr determined using inductively-coupled plasma mass spectrometry (ICP-MS). The ultrastructure of root, stem and leaf tissue was examined using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) in order to determine the sites of accumulation of Cr and to detect possible alterations in cell organelles induced by the presence of the metal. Chromium accumulated principally in the roots of the four macrophytes (8.6-30 mg kg(-1) dw), with much lower concentrations present in the stems and leaves (3.8-8.6 and 0.01-9.0 mg kg(-1) dw, respectively). Within root tissue, Cr was present mainly in the vacuoles of parenchyma cells and cell walls of xylem and parenchyma. Alterations in the shape of the chloroplasts and nuclei were detected in A. philoxeroides and B. scabiosoides, suggesting a possible application of these aquatic plants as biomarkers from Cr contamination.

Nickel: an overview of uptake, essentiality and toxicity in plants

Nickel even though recognized as a trace element, its metabolism is very decisive for certain enzyme activities, maintaining proper cellular redox state and various other biochemical, physiological and growth responses. Study of the aspects related with uptake, transport and distributive localization of Ni is very important in various cellular metabolic processes particularly under increased nitrogen metabolism. This review article, in core, encompasses the dual behavior of Ni in plants emphasizing its systemic partitioning, essentiality and ill effects. However, the core mechanism of molecules involved and the successive physiological conditions required starting from the soil absorption, neutralization and toxicity generated is still elusive, and varies among the plants.

Use of plasma-based spectroscopy and infrared microspectroscopy techniques to determine the uptake and effects of chromium(III) and chromium(VI) on Parkinsonia aculeata

Chromium uptake and tolerance by Mexican Palo Verde (Parkinsonia aculeata) (MPV) was studied in a six-month experiment with Cr(III) and Cr(VI) at 60 and 10 mg kg(-1), respectively. Chromium and nutrient uptake were determined by ICP-OES and changes in macromolecules were studied by infrared microspectroscopy (IMS). In the Cr(VI)-treated plants, chromium concentration increased in the roots only through the third month, while translocation to stems increased constantly throughout the six months. Cr(III) applications decreased the amount of Zn in leaves and stems (p < or = 0.05). Cr(VI) increased P and S in all plant tissues and increased Ca in roots, but decreased Ca in stems and leaves, and Mg in roots and stems. Cr(III) decreased P in stems and leaves, while both Cr ions decreased K in all MPV tissues. Relative to untreated plant tissue, the IMS revealed significant changes at 1730 cm(-1) and 845 cm(-1). Changes at 1730 cm(-1) indicated that the cortex and xylem of Cr-treated plants were more proteinaceous. Changes at 845 cm(-1) revealed higher lignifications in cortex. However, at the stem level, Cr(VI) decreased lignin deposition in xylem. The data showed that MPV could be useful in the phytoremediation of Cr in moderately impacted soils.

Toxic effects and specific chromium acquired resistance in selected strains of Dyctiosphaerium chlorelloides

Due to its various uses, chromium contamination has become widespread in a diverse array of environments. The present study was carried out to investigate the toxic effect of chromium exposures on sensitive and resistant strains of the green algae Dyctiosphaerium chlorelloides, and to determine the nature and mechanism of chromium-resistant cells that arise. The toxic effect on the photosynthetic performance of chromium exposures in both cell populations, and the sensitive differences due to chromium oxidation state, were estimated, and the results indicate that although the photosynthetic performance in both strains were inhibited, there are not significant differences among IC(50(72)) values obtained in toxicity assays with both chromium oxidation states in wild-type cells, and however these differences are very significant when the assays were performed with Cr(VI) resistant cells. The 72-h 50% inhibitory concentration values obtained with Cr(III) exposures were similar for both strains. Additionally, by means of the SEM/EDX and TEM microscopic techniques, the occurrence of rapid morphological evolution in the microalgal cells and the possible detoxificant mechanisms was observed after exposure of the wild strain to chromium hexavalent. Moreover, the different response in photosynthetic activity observed between sensitive and resistant cells of D. chlorelloides in the presence of Cr(VI) and Cr(III) could be used to obtain a chromium-specific eukaryotic microalgal biosensor.

Use of energy filtering transmission electron microscopy for image generation and element analysis in plant organisms

Energy filtering TEM (EFTEM) with modern spectrometers and software offers new possibilities for element analysis and image generation in plant cells. In the present review, applications of EFTEM in plant physiology, such as identification of light elements and ion transport, analyses of natural cell incrustations, determination of element exchange between fungi and rootlets during mycorrhiza development, heavy metal storage and detoxification, and employment in plant physiological experiments are summarized. In addition, it is demonstrated that EFTEM can be successfully used in more practical approaches, for example, in phytoremediation, food and wood industry, and agriculture. Preparation methods for plant material as prerequisites for EFTEM analysis are compared with respect to their suitability and technical problems are discussed.

In vivo monitoring of the potassium channel KcsA in Streptomyces lividans hyphae using immuno-electron microscopy and energy-filtering transmission electron microscopy

The previous discovery of theStreptomyces lividans kcsAgene and its overexpression followed by the functional reconstitution of the purified gene product has resulted in new strategies to explore this channel proteinin vitro. KcsA has evolved as a general model to investigate the structure/function relationship of ion channel proteins. Using specific antibodies raised against a domain of KcsA lacking membrane-spanning regions, KcsA has now been localized within numerous separated clusters between the outer face of the cytoplasm and the cell envelope in substrate hyphae of theS. lividanswild-type strain but not in a designed chromosomal disruption mutant ΔK, lacking a functionalkcsAgene. Previous findings had revealed that caesium ions led to a block of KcsA channel activity withinS. lividansprotoplasts fused to giant vesicles. As caesium can be scored by electron energy loss spectroscopy better than potassium, this technique was applied to hyphae that had been briefly exposed to caesium instead of potassium ions. Caesium was found preferentially at the cell envelope. Compared to the ΔK mutant, the relative level of caesium was ≈30 % enhanced in the wild-type. This is attributed to the presence of KcsA channels. Additional visualization by electron spectroscopic imaging supported this conclusion. The data presented are believed to represent the first demonstration ofin vivomonitoring of KcsA in its original host.

Analysis of element accumulation in cell wall attached and intracellular particles of snow algae by EELS and ESI

Snow algae frequently occur in alpine and polar permanent snow ecosystems and have developed adaptations to their harsh environment, where extreme temperature regimes high irradiation and low nutrient levels prevail. They live in a unique microhabitat, namely the liquid water between snow crystals. The predominant form appears as 'red snow' and in polar environment also 'green snow' frequently occurs. Light microscopy showed that most cells are densely covered by non-biotic particles of so far unknown composition. As snow normally contains very low amounts of nutrients, introduced mainly airborne like dust and precipitation, the inorganic particles at the surface of the snow algae may be important for their survival. By using electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), we investigated element distribution in ultrathin sections of snow algae from different polar (Svalbard, 5 m a.s.l., 79 degrees N and maritime Antarctic, King George Island, 10 m a.s.l., 62 degrees S) and alpine habitats (2400-3100 m a.s.l. Tyrol) for the present study. It turned out that the main elements of the cell wall attached particles are Si, Al, Fe and O independently from the origin of the snow algae. Interestingly, the same elements were also found in vacuolar compartments inside the cells. These vacuoles contain electron dense granules or crystals and are frequently found to be connected to the cortical cytoplasm. This finding suggests an uptake mechanism of the respective elements by pinocytosis. Co-transport of toxic aluminium together with silicon may be unavoidable as the inorganic nutrient uptake of the snow algae is limited to the thin water layer between the ice crystals. However, formation of insoluble aluminium silicates may serve as detoxification mechanism.