CLONING AND CHARACTERIZATION OF MAIZE HERBICIDE SAFENER-INDUCED CDNASENCODING SUBUNITS OF GLUTATHIONE-S-TRANSFERASE ISOFORM-I, ISOFORM-II AND ISOFORM-IV

Several GSTs have been characterised in maize. GST I is a homodimer of 29 kDa subunits, GST II a hetrodimer of 27 kDa and 29 kDa subunits an d GST IV a homodimer of 27 kDa subunits. We report the isolation and c haracterization of a herbicide-safener inducible cDNA clone, GST-27. B ased on partial amino acid sequence, GST-27 encodes the 27 kDa subunit present in both glutathione S-transferase isoforms GST II and IV. Nor thern blotting was used to compare the expression patterns of GST-27 w ith that of GST-29. Transcripts corresponding to GST-27 were found to be constitutively expressed in RNA isolated from the root, but no expr ession was detected in RNA isolated from aerial parts of the plant. Th e application of herbicide safener caused a dramatic increase in the e xpression of GST-27 in all aerial plant parts tested. GST-29 was found to be constitutively expressed in RNA isolated from a number of maize tis sues. The basal level of GST-29 expression showed a minimal incre ase upon herbicide safener treatment. Although a range of hormonal, en vironmental and physiological stimuli failed to elevate GST-27 levels, some increase in GST-27 mRNA was observed in the late stages of leaf senescence and after treatments resulting in phytotoxic effects.