INDUCTION OF ETHYLENE BIOSYNTHESIS IN NICOTIANA-TABACUM BY A TRICHODERMA-VIRIDE XYLANASE IS CORRELATED TO THE ACCUMULATION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID (ACC) SYNTHASE AND ACC OXIDASE TRANSCRIPTS

Xylanase (EIX) from the fungus Trichoderma viride elicits ethylene bio synthesis in leaf tissues of Nicotiana tabacum cv Xanthi but not in cv Hicks. The increase in ethylene biosynthesis is accompanied by an acc umulation of 1-aminocyclopropane-1-carboxylic acid (ACC), an increase in extractable ACC synthase activity, and increases in ACC synthase an d ACC oxidase transcripts. Priming of leaves with ethylene (120 mu L/L , 14 h) sensitizes the tissue, resulting in an enhanced response to EI X and increases in both the in vivo ACC oxidase activity and ACC oxida se transcript level. EIX and ethylene independently induce ACC oxidase . Inhibition of ethylene biosynthesis by aminoethoxyvinylglycine is no t accompanied by a reduction in ACC oxidase transcript level, indicati ng that ethylene biosynthesis is not required. In contrast to the diff erential induction of ethylene biosynthesis by EIX in Xanthi versus Hi cks cultivars, both cultivars respond to a chemical stress (induced by CUSO4) by enhancing ethylene production. This induction is accompanie d by an increase in ACC synthase transcript but not in that of ACC oxi dase.