Submergence enhances expression of a gene encoding 1-aminocyclopropane-1-carboxylate oxidase in deepwater rice

Partial submergence greatly stimulates internodal growth in deep water rice (Oryza sativa L.). Previous work has shown that the effect of submergence is, at least in part, mediated by ethylene, which accumulates in the air spaces of submerged internodes. To investigate the expression of the genes encoding ethylene biosynthetic enzymes during accelerated growth of deep water rice, we cloned a 1-aminocyclopropane-1-carboxylate (ACC) oxidase cDNA (OS-ACO1) from internodes of submerged plants and measured the activity of the enzyme in tissue extracts with an improved assay. We found an increase in ACC oxidase mRNA levels and enzyme activity after 4 to 24 h of submergence. Thus, it is likely that ethylene biosynthesis in internodes of deep water rice is controlled, at least in part, at the level of ACC oxidase.