Complexation of cadmium in seeds and vegetative tissues of the cadmium hyperaccumulator Thlaspi praecox as studied by X-ray absorption spectroscopy

Abstract

The cadmium hyperaccumulator Thlaspi praecox Wulfen (Brassicaceae) can accumulate unusually high amounts of Cd (>1,000 μg g −1 dry weight) in its seeds without drastically affecting seed viability. As embryonic tissues are the most sensitive to Cd toxicity, the aim of this study was to investigate the Cd coordination and ligand environment in seeds of field collected T. praecox using extended X-ray absorption fine structure (EXAFS), and to compare the Cd ligand environment to that in the vegetative tissues of the plant. In intact seeds and isolated embryos, almost two thirds of the Cd ligands were thiol groups (Cd-S-C-).In addition, there was coordination to phosphate groups via bridging oxygens (Cd-O-P-), as for phytate, although this ligand was not observed in the vegetative organs and tissues. In roots and shoots up to 80% of the Cd ligands were oxygen ligands that are provided by the cell walls and by organic acids stored in vacuoles. In leaf epidermis only a slightly higher percentage of oxygen ligands was detected, as compared to the mesophyll, making vacuolar compartmentation and binding to the cell walls the main detoxification mechanisms in both of these leaf tissues.

A Transcriptomic Network Underlies Microstructural and Physiological Responses to Cadmium in Populus × canescens

“…The induction of these antioxidants in cadmium-treated P. 3 canescens implies that these antioxidants play a pivotal role in scavenging excess ROS. The induction of these antioxidants, particularly thiols, and their role in cadmium detoxification have been documented in other plants (Vogel-Mikus et al, 2010;Gaudet et al, 2011;Seth et al, 2012). Overall, these data indicate that changes in internal nutrients, carbohydrates, and antioxidants play a role in physiological regulation of cadmium-exposed P. 3 canescens.…”

Histidine promotes the loading of nickel and zinc, but not of cadmium, into the xylem inNoccaea caerulescens

“…21 In accordance with this, the stability of the Cd-histidine complex is much lower than those of the Zn-histidine or Ni-histidine complexes. 22 In agreement with this, at least in hyperaccumulators, but probably also in most other plants, both Ni 6,8-10 and Zn 23 are predominantly coordinated with O and N, whereas Cd is largely coordinated with O and S, but barely or not with N. 24,25 Because hyperaccumulators barely accumulate phytochelatins upon Cd exposure, 26,27 it seems likely that glutathione (GSH) is their predominant low-molecular-weight, non-vacuolar Cd chelator. Since GSH has high affinity toward Cd, and is present at a high concentration in the cytoplasm, it is unlikely that exogenous histidine supply would lead to the formation of a Cd-histidine complex, which would in turn explain the absence of histidine-promoted Cd xylem loading.…”

Elemental distribution by cryo-micro-PIXE in the zinc and cadmium hyperaccumulator Sedum plumbizincicola grown naturally

“…Moreover, the complexation of Cl with heavy metals for example Cd, was reported to reduce the positive charge of the metal ions (Ozkutlu et al 2007). On the other hand, while it is known that in hyperaccumulators metals are predominantly bound by weak oxygen/nitrogen ligands, sulphur ligands represent approximately 30 % Cd in mature leaves of N. caerulescens and 20 % in the epidermis of mature leaves of N. praecox (Küpper et al 2004;Vogel-Mikuš et al 2010). Cd was more evenly distributed among the epidermis and mesophyll in the leaves of S. plumbizincicola, and thus differed from the Zn distribution.…”