Hyperaccumulation of cadmium and zinc in Thlaspi caerulescens and Arabidopsis halleri at the leaf cellular level.
Vacuolar compartmentalization or cell wall binding in leaves could play a major role in hyperaccumulation of heavy metals. However, little is known about the physiology of intracellular cadmium (Cd) sequestration in plants. We investigated the role of the leaf cells in allocating metal in hyperaccumulating plants by measuring short-term (109)Cd and (65)Zn uptake in mesophyll protoplasts of Thlaspi caerulescens "Ganges" and Arabidopsis halleri, both hyperaccumulators of zinc (Zn) and Cd, and T. caerulescens "Prayon," accumulating Cd at a lower degree. The effects of low temperature, several divalent cations, and pre-exposure of the plants to metals were investigated. There was no significant difference between the Michaelis-Menten kinetic constants of the three plants. It indicates that differences in metal uptake cannot be explained by different constitutive transport capacities at the leaf protoplast level and that plasma and vacuole membranes of mesophyll cells are not responsible for the differences observed in heavy metal allocation. This suggests the existence of regulation mechanisms before the plasma membrane of leaf mesophyll protoplasts. However, pre-exposure of the plants to Cd induced an increase in Cd accumulation in protoplasts of "Ganges," whereas it decreased Cd accumulation in A. halleri protoplasts, indicating that Cd-permeable transport proteins are differentially regulated. The experiment with competitors has shown that probably more than one single transport system is carrying Cd in parallel into the cell and that in T. caerulescens "Prayon," Cd could be transported by a Zn and Ca pathway, whereas in "Ganges," Cd could be transported mainly by other pathways.
Cosio
Claudia
C
Institut des Sciences et techniques de l'environnement-Laboratoire de pedologie, Faculté d'environnement naturel architectural et carstruit, Ecole Polytechnique Féderale de Lausanne, Lausanne, Switzerland. claudia.cosio@epfl.ch
Martinoia
Enrico
E
Keller
Catherine
C
D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002104:Cadmium / Q000378:metabolism* / Q000494:pharmacology; D002106:Cadmium Radioisotopes / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000378:metabolism; D002412:Cations / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003080:Cold Temperature; D018515:Plant Leaves / Q000378:metabolism*; D031227:Thlaspi / Q000187:drug effects / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology; D015032:Zinc / Q000378:metabolism* / Q000494:pharmacology; D015037:Zinc Radioisotopes / Q000378:metabolism
D002106:Cadmium Radioisotopes; D002121:Calcium Channel Blockers; D027682:Cation Transport Proteins; D002412:Cations; D015037:Zinc Radioisotopes; D002104:Cadmium; D014700:Verapamil; D015032:Zinc