Distribution of cadmium in leaves of Thlaspi caerulescens

Abstract

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 microM) 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.

The changes of contents of selected free amino acids associated with cadmium stress in Noccaea caerulescens and Arabidopsis halleri

“…This finding corresponded with the results of Rascio and Navari-Izzo (2011). In comparison to NC, Cd contents in aboveground biomass of AH were lower at all Cd treatments (Table 3), but they were above the 100 mg/kg Cd threshold that defined Cd hyperaccumulation in the natural environment (Cosio et al 2005). The opposite effects were observed in control variants -higher Cd contents in AH in contrast to NC were determined.…”

Tolerance and prospection of phytoremediator woody species of Cd, Pb, Cu and Cr

“…Their genotoxic effects depend on the oxidation state of the metal, their concentration and the duration of exposition, and these are more pronounced at high concentrations and after a long exposition time (Cosio et al, 2005). Cytological analyses demonstrate numerous aberrations of chromosomes in meristematic root tissue of seedlings developed from seeds collected from trees in the polluted area, including chromosome bridges and stickiness, laggards, retarded and forward chromosomes, and their fragments (Prus-Glowacki et al, 2006).…”

“…Plant tolerance and/or resistance to metallic stress can be associated with one or more mechanisms, such as: (i) the excretion of chelating compounds that reduce the availability of the metal in the soil or water; (ii) the exclusion of the metal through selective absorption of elements; (iii) the retention of the metal in roots, preventing its translocation to the aerial part; (iv) the chelation or sequestration of heavy metals by ligands, compartmentalization, biotransformation and mechanisms of cellular repair; (v) the development of enzymes tolerant to the metal (Hall, 2002;Cobbett and Goldsbrough, 2002;Patra et al, 2004); (vi) the increase of production of intracellular compounds linked to the metal (Sharma and Dietz, 2006); (vii) the immobilization of the metal in the cellular wall (Cosio et al, 2005); (viii) homeostatic cellular mechanisms to regulate the concentration of metal ions inside the cell (Benavides et al, 2005); (ix) induction of heat-shock proteins (Heckathorn et al, 2004); (x) release of phenols from roots (Jung et al, 2003); (xi) the increase of tolerance to mineral deficiency or the decrease of nutritional requirements; (xii) the increase in absorption of certain macronutrients; and (xiii) the development of the capacity to absorb and to use minerals in the presence of heavy metals (Meda et al, 2007). As a result of these tolerance and/or resistance mechanisms (alone or in combination), some plants can grow in environments contaminated with metals where other species do not survive (Hall, 2002).…”

Nitrate facilitates cadmium uptake, transport and accumulation in the hyperaccumulator Sedum plumbizincicola

“…109 Cd has also been widely used to visualise Cd distribution within plant tissues by autoradiography (Cosio et al 2005). However, only the static distribution of Cd at a given moment can be obtained by autoradiography.…”