The Role in Ozone Phytotoxicity of the Evolution of Ethylene upon Induction of 1-Aminocydopropane-1-carboxylic Acid Synthase by Ozone Fumigation in Tomato Plants

Abstract

The rate of evolution of ethylene by tomato plants was rapidly increased by O₃ fumigation. The time course of the increase in 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity was the same as that in the rate of evolution of ethylene, suggesting that ACC synthase activity might be a rate-limiting step in the evolution of ethylene that is caused by O₃ fumigation. The rate of the O₃-induced evolution of ethylene was increased by the application of ACC to tomato plants, suggesting the involvement of ACC oxidase in the O₃-induced evolution of ethylene. Treatment of plants with tiron inhibited the evolution of ethane, but not of ethylene. These results indicated that evolution of ethylene in O₃-treated tomato plants might result from enzymatic reactions catalyzed by both ACC synthase and ACC oxidase, but not from stimulation by O₃ of the peroxidation of lipids mediated by free radicals. Pretreatment of leaves with aminoethoxyvinylglycine (AVG), an inhibitor of ACC synthase, significantly inhibited the evolution of ethylene that was induced by O₃ and concomitantly reduced the extent of O₃-induced visible damage to leaves. Treatment with 2,5-norbonadiene, an inhibitor of the action of ethylene, strongly reduced the extent of visible damage caused by O₃, even though it did not suppress the evloution of ethylene. These results indicate that ethylene acts on certain metabolic processes to cause visible damage.