Induction of Ethylene Biosynthesis in Nicotiana tabacum

Xylanase (EIX) from the fungus Trichoderma viride elicits ethylene biosynthesis in leaf tissues of Nicotiana tabacum cv Xanthi but not in cv Hicks. The increase in ethylene biosynthesis is accompanied by an accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC), an increase in extractable ACC synthase activity, and increases in ACC synthase and ACC oxidase transcripts. Priming of leaves with ethylene (120 pL/L, 14 h) sensitizes the tissue, resulting in an enhanced response to EIX and increases in both the in vivo ACC oxidase activity and ACC oxidase transcript level. EIX and ethylene independently induce ACC oxidase. Inhibition of ethylene biosynthesis by aminoethoxyvinylglycine is not accompanied by a reduction in ACC oxidase transcript level, indicating that ethylene biosynthesis is not required. In contrast to the differential induction of ethylene biosynthesis by EIX in Xanthi versus Hicks cultivars, both cultivars respond to a chemical stress (induced by CuSO,) by enhancing ethylene production. This induction is accompanied by an increase in ACC synthase transcript but not in that of ACC oxidase.