METHYL JASMONATE INDUCES AN O-METHYLTRANSFERASE IN BARLEY

We have previously described a truncated cDNA clone for a barley (Hord eum vulgare L. cv. Salome) jasmonate regulated gene, JRG5, which shows homology to caffeic acid O-methyltransferase (COMT). A cDNA encompass ing the coding region was amplified by PCR and cloned for overexpressi on in E. coli. Western blot analyses indicate that the recombinant pro tein crossreacts with the antibodies directed against the tobacco clas s II OMT and only weakly with the antibodies for the tobacco class I O MT. An immunoreactive band in the protein extract of jasmonate-treated leaf segments suggests that JRG5 transcripts that accumulate after ja smonate treatment are also translated. Specific methylating activities on caffeic acid and catechol were obtained from the recombinant prote in through renaturation of protein extracted from inclusion bodies or from bacteria grown and induced at low temperature. On Northern blots, the JRG5 transcripts were detected in the leaf sheath but not the lea f lamina, stem, root or inflorescence and accumulated in leaf segments after jasmonate application. Several hormone or stress treatments did not induce JRG5 mRNA accumulation. This includes sorbitol stress whic h is known to lead to enhanced endogenous jasmonate levels and the imp lications for jasmonate signaling are discussed. Based on quantitative measurements and fluorescence microscopy, jasmonate-induced accumulat ion of ferulic acid and phenolic polymers in the cell wall were detect ed and the possibility of cell wall strengthening mediated through phe nolic crosslinks is discussed.