Rapid induction of a novel ACC synthase gene in deepwater rice seedlings upon complete submergence

Elongation growth is a typical feature of deepwater rice plants in response to submergence. The growth phenomenon is known to be induced by hypoxia, w hich results in the expression of genes implicated in ethylene biosynthesis . Ethylene is considered to trigger the growth response as it accumulates i n the submerged tissues and submergence enhances the expression of 1-aminoc yclopropane-1-carboxylate (ACC) synthase. However, ACC concentration in ric e plants increases much faster after submergence than the activity of the A CC synthase genes studied previously. Here, we studied the expression chara cteristics of the fifth member of this gene family, OS-ACS5, and show that submergence induces the messenger concentration of this gene before the acc umulation of ACC could be observed. OS-ACS5 may play a fundamental role in the growth-promoting increase in ethylene biosynthesis during the first hou rs of submergence in deepwater rice.