Overview of known GST functions in plants. (a) In secondary metabolism, GSTs detoxify toxins by conjugation with GSH; the conjugates (toxin-SG) are then transported into the vacuole by ABC transporters (shown as circles) prior to proteolytic processing. (b) Some phi and tau class enzymes are also required for transport of flavonoid pigments to the vacuole. (c-e) Roles of GSTs in stress metabolism include acting as (c) glutathione peroxidases that can reduce cytotoxic DNA and lipid hydroperoxides; (d) in an antioxidant capacity, protecting against Bax-induced cell death; and (e) in stress signaling, playing a role in the induction of chalcone synthase following exposure to ultraviolet light. Finally, zeta GSTs (GSTZ) have a role in primary metabolism as maleylacetoacetate isomerases. Wide arrows denote an induction process; narrow arrows denote enzymatic reactions; thick lines denote inhibition of a reaction; R, an alkyl group.