INDUCTION OF AN ACC SYNTHASE CDNA BY OZONE IN LIGHT-GROWN ARABIDOPSIS-THALIANA LEAVES

The rate-limiting enzyme in the ethylene biosynthesis pathway is 1-ami nocyclopropane-1-carboxylate (ACC) synthase. We have investigated an o zone (O-3)-induced ACC synthase gene in Arabidopsis thaliana. Four pre viously reported ACC synthase genes from A. thaliana (ACS1, ACS2, ACS4 and ACS5) were nor induced in response to O-3 stress. An O-3-induced 1098-bp cDNA encoding ACC synthase was isolated from foliage of A. tha liana; this sequence was identical to that of ACS6 which could be indu ced by multiple stimuli including touch. When plants were treated with 350 nl l(-1) of O-3 for 2 or 6 h; the evolution of ethylene became ma ximal after 1.5 h and gradually decreased thereafter. Similarly, the m RNA transcript of O-3-induced ACC synthase was detected after 30 min o f exposure, attained a maximum level after 1 h, and then declined. Vis ible damage in O-3-treated plants was observed at the end of the 2-h e xposure. This ACC synthase gene in A. thaliana provides a useful tool for studying O-3-induced responses related to ethylene production at t he molecular and genetic levels.