XVI International Botanical Congess

Most metabolites and inorganic ions are accumulated within the vacuole by the electrochemical potential. In contrast, vacuolar uptake of glutathione conjugates (GS-X) is directly energized by ATP. Further investigations showed that several other non-biotic and biotic conjugates are also transported into the vacuole by direct energization. Furthermore our results suggest that these transporters show allosteric modulation. A database search for plant proteins homologous to MRP1 and YCF1, which have already been shown to be GS-X transporters revealed that several highly similar proteins in Arabidopsis thaliana. We cloned one member of this family and expressed it in the yeast ycf1 mutant. This plant MRP homologue restored cadmium tolerance and GS-X transport activity. Surprisingly, the plant gene product was also able to transport chlorophyll catabolites, which where shown to be transported into the vacuole by ABC-transporter type kinetics but which did not interfere with GS-X.