CLARIFICATION OF MECHANISM OF SUBMERGENCE-TOLERANCE USING A SUBMERGENCE-TOLERANT RICE CULTIVAR

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The visual damage of submergence usually develops after desubmergence. A part of the damage may be caused by active oxygen produced in transition of oxygen environment. The submergence-intolerant rice cultivar, IR42 suffered from more lipid peroxidation with the production of HィイD22ィエD2OィイD22ィエD2 than submergence-tolerant cultivar, FR13A, after desubmergence. The activities of active oxygen scavenging enzymes in both cultivars were about the same or higher relative to the nonsubmerged control. After 6d of submergence, the total ascorbate levels in both cultivars decreased by 81% and 55% for IR42 and FR13A, respectively. During 7d of recovery after desubmergence, however, FR13A increased level of total ascorbate up to 150% while IR42 did it up to only 78%. Moreover, the proportion of ascorbic acid to total ascorbate I FR13A increased significantly after 3d of recovery and reached the level of that in nonsubmerged control, but the proportion in IR42 was still low during the recovery phase. It means that FR13A could operate the AOS scavenging system better than IR42 after desubmergence. It is suggested that the AOS may be one of the causes of the damage after desubmergence and ascorbate may take ana active role in alleviating the damage.Three cDNA fragments were isolated by differential screening between FR13A desubmerged for 2days after seven days' submergence was cancelled, and non-submerged control FR13A. The one was a giberellin-synthesis-related gene, the second was a proteasome-related gene, and the third was a tolerant gene to pathogenic microorganisms.