Subcellular localisation of Cd and Zn in the leaves of a Cd-hyperaccumulating ecotype of Thlaspi caerulescens (original) (raw)
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New Phytologist, 2009
• Differential sorption and transport characteristics of the leaf mesophyll layer of the Prayon and Ganges ecotypes of the hyperaccumulator Thlaspi caerulescens were examined.• 109Cd influx and efflux experiments were conducted with leaf sections, and X-ray absorption near edge structure (XANES) data were collected from leaves as a general comparison of in vivo cadmium (Cd) coordination.• There were modest differences in cell wall sorption of Cd between ecotypes. There were obvious differences in time- and concentration-dependent Cd influx, including a greater VMAX for Prayon but a lower KM for Ganges for concentration-dependent Cd uptake and a notably greater Cd uptake by Ganges leaf sections at 1000 µm Cd. Leaf sections of Prayon had a greater Cd efflux than Ganges. The XANES spectra from the two ecotypes suggested differences in Cd coordination.• The fundamental differences observed between the two ecotypes may reflect differential activity and/or expression of plasma membrane and tonoplast transporters. More detailed study of these transporters and the in vivo coordination of Cd are needed to determine the contribution of these processes to metal homeostasis and tolerance.Differential sorption and transport characteristics of the leaf mesophyll layer of the Prayon and Ganges ecotypes of the hyperaccumulator Thlaspi caerulescens were examined.109Cd influx and efflux experiments were conducted with leaf sections, and X-ray absorption near edge structure (XANES) data were collected from leaves as a general comparison of in vivo cadmium (Cd) coordination.There were modest differences in cell wall sorption of Cd between ecotypes. There were obvious differences in time- and concentration-dependent Cd influx, including a greater VMAX for Prayon but a lower KM for Ganges for concentration-dependent Cd uptake and a notably greater Cd uptake by Ganges leaf sections at 1000 µm Cd. Leaf sections of Prayon had a greater Cd efflux than Ganges. The XANES spectra from the two ecotypes suggested differences in Cd coordination.The fundamental differences observed between the two ecotypes may reflect differential activity and/or expression of plasma membrane and tonoplast transporters. More detailed study of these transporters and the in vivo coordination of Cd are needed to determine the contribution of these processes to metal homeostasis and tolerance.
Distribution of cadmium in leaves of Thlaspi caerulescens
Journal of Experimental Botany, 2005
Knowledge of the intracellular distribution of Cd in leaves is necessary in order to understand the mechanisms of hyperaccumulation in Thlaspi caerulescens. Ganges and Prayon, two ecotypes accumulating Cd to different levels, were grown in nutrient medium containing varying concentrations (0, 5, 10, 50, and 100 lM) of Cd. Several different approaches were combined in this study to (i) validate the results obtained by a specific method and (ii) establish the link between observations and measurements performed at different scales. In both ecotypes, Cd, localized by autoradiography, was found mainly at the edges of the leaves, but also in points of higher concentration spread over the whole limb surface. This localization was clearly correlated with the necrotic spots observed on Prayon leaves. Scanning electron microscopy coupled with energy dispersive X-ray microanalysis (cryo-SEM-EDXMA) and tissue fractionation (apoplasm, cell walls, mesophyll protoplasts, and lower epidermis) showed that Cd had similar patterns of distribution in leaf cells of both ecotypes. Cadmium was found both inside the cells and in the cell walls, mainly in the large epidermal cells but also in small epidermal cells. All the methods used agreed well and the results indicated that metal storage in the plants studied involves more than one compartment and that Cd is stored principally in the less metabolically active parts of leaf cells.
PLANT PHYSIOLOGY, 2004
Extended x-ray absorption fine structure measurements were performed on frozen hydrated samples of the cadmium (Cd)/zinc (Zn) hyperaccumulator Thlaspi caerulescens (Ganges ecotype) after 6 months of Zn 2ϩ treatment with and without addition of Cd 2ϩ . Ligands depended on the metal and the function and age of the plant tissue. In mature and senescent leaves, oxygen ligands dominated. This result combined with earlier knowledge about metal compartmentation indicates that the plants prefer to detoxify hyperaccumulated metals by pumping them into vacuoles rather than to synthesize metal specific ligands. In young and mature tissues (leaves, petioles, and stems), a higher percentage of Cd was bound by sulfur (S) ligands (e.g. phytochelatins) than in senescent tissues. This may indicate that young tissues require strong ligands for metal detoxification in addition to the detoxification by sequestration in the epidermal vacuoles. Alternatively, it may reflect the known smaller proportion of epidermal metal sequestration in younger tissues, combined with a constant and high proportion of S ligands in the mesophyll. In stems, a higher proportion of Cd was coordinated by S ligands and of Zn by histidine, compared with leaves of the same age. This may suggest that metals are transported as stable complexes or that the vacuolar oxygen coordination of the metals is, like in leaves, mainly found in the epidermis. The epidermis constitutes a larger percentage of the total volume in leaves than in stems and petioles. Zn-S interaction was never observed, confirming earlier results that S ligands are not involved in Zn resistance of hyperaccumulator plants. fax 607-255-2459. Article, publication date, and citation information can be found at http://www.plantphysiol.org/cgi/
New Phytologist, 2008
Localization of cadmium (Cd) and other elements was studied in the leaves of the field-collected cadmium/zinc (Cd/Zn) hyperaccumulator Thlaspi praecox from an area polluted with heavy metals near a lead mine and smelter in Slovenia, using micro-PIXE (proton-induced X-ray emission). • The samples were prepared using cryofixation. Quantitative elemental maps and average concentrations in whole-leaf cross-sections and selected tissues were obtained.
New Phytologist, 2007
• In this study we address the impact of changes in plant heavy metal, (i.e. zinc (Zn) and cadmium (Cd)) status on metal accumulation in the Zn/Cd hyperaccumulator, Thlaspi caerulescens.• Thlaspi caerulescens plants were grown hydroponically on both high and low Zn and Cd regimes and whole-shoot and -root metal accumulation, and root 109Cd2+ influx were determined.• High-Zn-grown (500 µm Zn) plants were found to be more Cd-tolerant than plants grown in standard Zn conditions (1 µm Zn). Furthermore, shoot Cd accumulation was significantly greater in the high-Zn-grown plants. A positive correlation was also found between shoot Zn accumulation and increased plant Cd status. Radiotracer 109Cd root flux experiments demonstrated that high-Zn-grown plants maintained significantly higher root Cd2+ influx than plants grown on 1 µm Zn. It was also found that both nickel (Ni) and copper (Cu) shoot accumulation were stimulated by high plant Zn status, while manganese (Mn) accumulation was not affected.• A speculative model is presented to explain these findings, suggesting that xylem loading may be one of the key sites responsible for the hyperaccumulation of Zn and Cd accumulation in Thlaspi caerulescens.In this study we address the impact of changes in plant heavy metal, (i.e. zinc (Zn) and cadmium (Cd)) status on metal accumulation in the Zn/Cd hyperaccumulator, Thlaspi caerulescens.Thlaspi caerulescens plants were grown hydroponically on both high and low Zn and Cd regimes and whole-shoot and -root metal accumulation, and root 109Cd2+ influx were determined.High-Zn-grown (500 µm Zn) plants were found to be more Cd-tolerant than plants grown in standard Zn conditions (1 µm Zn). Furthermore, shoot Cd accumulation was significantly greater in the high-Zn-grown plants. A positive correlation was also found between shoot Zn accumulation and increased plant Cd status. Radiotracer 109Cd root flux experiments demonstrated that high-Zn-grown plants maintained significantly higher root Cd2+ influx than plants grown on 1 µm Zn. It was also found that both nickel (Ni) and copper (Cu) shoot accumulation were stimulated by high plant Zn status, while manganese (Mn) accumulation was not affected.A speculative model is presented to explain these findings, suggesting that xylem loading may be one of the key sites responsible for the hyperaccumulation of Zn and Cd accumulation in Thlaspi caerulescens.
Plant Cell and Environment, 2008
A detailed localization of elements in leaf tissues of the field-collected Cd/Zn hyperaccumulator Thlaspi praecox (Brassicaceae) growing at a highly metal-polluted site was determined by micro-proton-induced X-ray emission (micro-PIXE) in order to reveal and compare nutrient and non-essential element accumulation patterns in the case of multiple metal accumulation within particular leaf tissues, including the detailed distribution between apoplast and symplast regions. On the larger scans, the highest concentrations of metals were observed in the epidermis, S and Ca in the palisade mesophyll, Cl in the spongy mesophyll and vascular bundles, and P and K in the vascular bundles. On the more detailed scans, the highest Cd, Pb, Cl and K concentrations were observed in vascular bundle collenchyma. The relative element distribution (%) was calculated based on concentrations of elements in particular leaf tissues and their relative weight portions, indicating that most of the accumulated Zn was located in epidermises, while the majority of Cd and Pb was distributed within the mesophyll. Detailed scans of epidermal/mesophyll tissues revealed that Zn was mainly accumulated and detoxified in the symplast of large vacuolated epidermal cells, Cd in the mesophyll symplast, and Pb in the mesophyll symplast and apoplast.
Cadmium and zinc share many similar physiochemical properties, but their 4 compartmentation, complexation and impact on other mineral element distribution in plant 5 tissues may drastically differ. In this study, we address the impact of 10-µM Cd or 50-µM Zn 6 treatment on ion distribution in leaves of a metallicolous population of the non-7 hyperaccumulating species Zygophyllum fabago at tissue and cell level, and the consequences 8 on the plant response through a combined physiological, proteomic and metabolite approach. 9
Journal of Hazardous Materials, 2011
Potentilla griffithii Hook is a newly found hyperaccumulator plant capable of high tolerance and accumulation of Zn and Cd. We investigated the interactive effects between Cd and Zn on accumulation and vacuolar sequestration in P. griffithii. Stimulatory effect of growth was noted at 0.2 mM Cd and 1.25 and 2.5 mM Zn tested. Accumulation of Zn and Cd in roots, petioles and leaves were increased significantly with addition of these metals individually. However, the Zn supplement decreased root Cd accumulation but increased the concentration of Cd in petioles and leaves. The results from sub-cellular distribution showed that up to 94% and 70% of the total Zn and Cd in the leaves were present in the protoplasts, and more than 90% Cd and Zn in the protoplasts were localized in the vacuoles. Nearly, 88% and 85% of total Cd and Zn were extracted in the cell sap of the leaves suggesting that most of the Cd and Zn in the leaves were available in soluble form. The present results indicate that Zn supplement significantly enhanced the petiole accumulation of Cd and further vacuolar sequestration plays an important role in tolerance, detoxification and hyperaccumulation of these metals in P. griffithii.
Physiological responses to Cd and Zn in two Cd/Zn hyperaccumulating Thlaspi species
Environmental and Experimental Botany, 2009
In a model hyperaccumulation study a Cd/Zn hyperaccumulator Thlaspi caerulescens accession Ganges and a recently reported Cd/Zn hyperaccumulator Thlaspi praecox grown in increasing Cd and Zn concentrations in the substrate and in field collected polluted soil were compared. Plant biomass, concentrations of Cd and Zn, total chlorophylls and anthocyanins, antioxidative stress parameters and activities of selected antioxidative enzymes were compared. Increasing Cd, but not Zn in the substrate resulted in the increase of biomass of roots and shoots of T. praecox and T. caerulescens. The two species hyperaccumulated Cd in the shoots to a similar extent, whereas T. caerulescens accumulated more Zn in the shoots than T. praecox. Cadmium amendment decreased total chlorophyll concentration and glutathione reductase activity, and increased non-protein thiols concentration only in T. praecox, suggesting that it is less tolerant to Cd than T. caerulescens. In the field-contaminated soil, T. caerulescens accumulated higher Cd concentrations; but as T. praecox produced higher biomass, both species have similar ability to extract Cd.