An inducible glutathione S-transferase in soybean hypocotyl is localized in the apoplast

Glutathione S-transferases (GSTs) with additional activities as fatty acid hydroperoxidases were investigated in soybean (Glycine max L.) hypocotyls. Aside from the GSTs present in total soluble tissue extracts, enzyme activities and distinct immunoreactive CST polypeptides were also detected in the intercellular washing fluid. Whereas the intracellular isoenzymes were both constitutive and inducible, apoplastic CST and glutathione peroxidase was detectable only in tissues treated with the known CST inducer 2,3,5-triiodobenzoic acid. Monensin inhibited the induced accumulation of apoplastic GST but did not affect the intracellular isoforms. The discovery of apoplastic inducible CST will be discussed in light of the putative function of these enzymes in plants.