Abstract
While exogenous toxic compounds such as herbicides are thought to be sequestered into vacuoles in the form of glutathione (GSH) conjugates, little is understood about natural plant products conjugated with GSH. To identify natural products conjugated with GSH in plants, metabolites in the Arabidopsis γ-glutamyl transpeptidase (ggt) 4 knockout mutants that are blocked in the degradation of GSH conjugates in the vacuole were compared with those in wild-type plants. Plants were infected with a pathogen because a phytoalexin in Vigna radiata, was previously shown to conjugate with GSH in vitro (Li et al. 1997) and oxylipins, whose GSH conjugates were detected in vivo, was previously found to be induced by the pathogen (Mueller et al. 2008). Metabolites were analyzed using CE -TOF/MS. Among the metabolites accumulated in ggt4 mutants, one was confirmed to be the 12-oxo-phytodienoic acid (OPDA)-GSH conjugate. OPDA is a precursor of jasmonic acid. OPDA-GSH was increased upon the pathogen infection and this was concomitant with the increase in OPDA. This indicates that a certain portion of OPDA was transported into the vacuole in the form of GSH conjugate.
