EXPRESSION CHARACTERISTICS OF OS-ACS1 AND OS-ACS2, 2 MEMBERS OF THE 1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE GENE FAMILY IN RICE (ORYZA-SATIVA L CV HABIGANJ AMAN-II) DURING PARTIAL SUBMERGENCE

Deepwater rice can grow in the regions of Southeast Asia that are floo ded during the monsoon season because it has several adaptations allow ing it to survive under flooded conditions. One such adaptation is the ability for rapid internode elongation upon partial submergence to ma intain its foliage above the rising flood water levels. Ethylene is co nsidered to be the trigger of this growth response because deepwater c onditions not only trap ethylene in submerged organs, but also enhance the activity of 1-aminocyclopropane-1-carboxylate (ACC) synthase. Her ein we have studied the expression characteristics of two members of t he five-member multigene family encoding ACC synthase in rice OS-ACS1 and OS-ACS2 and show that partial submergence induces expression of OS -ACS1 and suppresses expression of OS-ACS2. The induction of OS-ACS1 o ccurs within 12 h oi partial submergence and al low oxygen concentrati ons. The data also suggest that deepwater conditions posttranscription ally regulate ACC synthase activity. OS-ACS1 gene expression may contr ibute to longer-term ethylene production, but not to the initial, grow th-promoting increase in ethylene synthesis.