Abstract
Ozone, a major photochemical oxidant, induces salicylic acid (SA) synthesis prior to exhibit leaf damage. To identify the pathway for ozone-induced SA synthesis, the level of SA and mRNA for the enzymes shown to be participated in SA synthesis were investigated with ozone exposed tobacco leaves. The level of SA became a peak at 6h ozone-exposure. At the time, mRNA for phenylalanine ammonia-lyase (PAL) and chorismate mutase increased remarkably with concomitant increase in PAL activity. These phenomena were diminished in ozone-exposed transgenic tobacco that exhibited reduced ozone-induced ethylene production. The level of transcript for isochorismate synthase was decreased in both wild type and transgenic plants during 6h-ozone exposure. These results suggest that SA may be synthesized from phenylalanine in ozone-exposed tobacco and ozone-induced SA accumulation may be regulated by ethylene.
