Cadmium sorption, influx, and efflux at the mesophyll layer of leaves from ecotypes of the Zn/Cd hyperaccumulator Thlaspi caerulescens

Abstract

Summary• Differential sorption and transport characteristics of the leaf mesophyll layer of the Prayon and Ganges ecotypes of the hyperaccumulator Thlaspi caerulescens were examined.• 109 Cd 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 V MAX for Prayon but a lower K M 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.

Advances in Phytoremediation Research: A Case Study of Gynura Pseudochina (L.) DC.

“…The net Zn-uptake rate increased as the Zn-concentration in the growth solution increased, because the greater the external concentration of Zn, the higher were both Zn-influx and Zn-efflux (Santa-Maria & Cogliatti, 1998). In addition, the enhancement of Cd uptake under dually Zn and Cd treatment might be attributed to an altered and specialized transporter of metal ions in the plasma membrane system induced by the addition of Zn (Ebbs et al, 2009). …”

Influence of CdCl2 and CdSO4 supplementation on Cd distribution and ligand environment in leaves of the Cd hyperaccumulator Noccaea (Thlaspi) praecox

“…This mainly involves the TcZNT5 metal transporter, which is more abundant in the plasma membrane of epidermal storage cells than in other cell types (Leitenmaier and Küpper 2011). Although epidermal storage cells can have higher metal concentrations than mesophyll cells, it is the mesophyll tissue layer that harbours the greater total mass of metal Vogel-Mikuš et al 2008;Ebbs et al 2009). The involvement of the leaf mesophyll in metal hyperaccumulation and tolerance is reasonable, as mesophyll cells are much more abundant and are positioned between the vascular bundles (representing a source of metals in the leaves after xylem loading) and the epidermal cells (Ebbs et al 2009).…”

“…Although epidermal storage cells can have higher metal concentrations than mesophyll cells, it is the mesophyll tissue layer that harbours the greater total mass of metal Vogel-Mikuš et al 2008;Ebbs et al 2009). The involvement of the leaf mesophyll in metal hyperaccumulation and tolerance is reasonable, as mesophyll cells are much more abundant and are positioned between the vascular bundles (representing a source of metals in the leaves after xylem loading) and the epidermal cells (Ebbs et al 2009). In a study that compared Cd sorption and transport characteristics in the leaf mesophyll layer of the N. caerulescens ecotypes of Prayon (Zn/Cd hyperaccumulator) and Ganges (Cd/Zn hyperaccumulator) (Ebbs et al 2009), a clear difference in Cd efflux between these two ecotypes was shown, with Prayon showing higher efflux rates.…”

“…The involvement of the leaf mesophyll in metal hyperaccumulation and tolerance is reasonable, as mesophyll cells are much more abundant and are positioned between the vascular bundles (representing a source of metals in the leaves after xylem loading) and the epidermal cells (Ebbs et al 2009). In a study that compared Cd sorption and transport characteristics in the leaf mesophyll layer of the N. caerulescens ecotypes of Prayon (Zn/Cd hyperaccumulator) and Ganges (Cd/Zn hyperaccumulator) (Ebbs et al 2009), a clear difference in Cd efflux between these two ecotypes was shown, with Prayon showing higher efflux rates. This suggests that the Cd taken up by Ganges mesophyll cells might be more effectively sequestered into the vacuoles, which decreases the need for efflux to achieve homeostasis in mesophyll cells (Ebbs et al 2009).…”

“…In a study that compared Cd sorption and transport characteristics in the leaf mesophyll layer of the N. caerulescens ecotypes of Prayon (Zn/Cd hyperaccumulator) and Ganges (Cd/Zn hyperaccumulator) (Ebbs et al 2009), a clear difference in Cd efflux between these two ecotypes was shown, with Prayon showing higher efflux rates. This suggests that the Cd taken up by Ganges mesophyll cells might be more effectively sequestered into the vacuoles, which decreases the need for efflux to achieve homeostasis in mesophyll cells (Ebbs et al 2009). The Prayon and Ganges ecotypes differ also according to the Cd ligand environment in mesophyll cells, where Ganges showed a significantly higher portion of sulphur-based Cd ligands (S-ligands), while Prayon showed a larger portion of oxygen-based Cd ligands (O-ligands), which was attributed to the cell-wall components (Ebbs et al 2009).…”