Vacuolar sequestration of glutathione S-conjugates outcompetes a possible degradation of the glutathione moiety by phytochelatin synthase.
Monochlorobimane was used as a model xenobiotic for Arabidopsis to directly monitor the compartmentation of glutathione-bimane conjugates in situ and to quantify degradation intermediates in vitro. Vacuolar sequestration of the conjugate was very fast and outcompeted carboxypeptidation to the gamma-glutamylcysteine-bimane intermediate (gamma-EC-B) by phytochelatin synthase (PCS) in the cytosol. Following vacuolar sequestration, degradation proceeded to cysteine-bimane without intermediate. Only co-infiltration of monochlorobimane with Cd2+ and Cu2+ increased gamma-EC-B formation to 4% and 25%, respectively, within 60 min. The role of PCS under simultaneous heavy metal stress was confirmed by investigation of different pcs1 null-mutants. In the absence of elevated heavy metal concentrations glutathione-conjugates are therefore first sequestered to the vacuole and subsequently degraded with the initial breakdown step being rate-limiting.
Grzam
Anke
A
Heidelberg Institute of Plant Sciences, University of Heidelberg, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany.
Tennstedt
Pierre
P
Clemens
Stephan
S
Hell
Rüdiger
R
Meyer
Andreas J
AJ
D019881:Aminoacyltransferases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002104:Cadmium / Q000378:metabolism / Q000494:pharmacology; D002474:Cell-Free System / Q000378:metabolism; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism*; D009154:Mutation; D018515:Plant Leaves / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D030821:Plants, Genetically Modified / Q000201:enzymology; D011720:Pyrazoles / Q000378:metabolism / Q000494:pharmacology; D014617:Vacuoles / Q000201:enzymology* / Q000235:genetics; D015262:Xenobiotics / Q000378:metabolism / Q000494:pharmacology
D029681:Arabidopsis Proteins; D011720:Pyrazoles; D015262:Xenobiotics; D002104:Cadmium; C059597:monochlorobimane; D003300:Copper; D019881:Aminoacyltransferases; C502365:AT5G44070 protein, Arabidopsis; D005978:Glutathione