9407763 Kende Deepwater rice (Oryza sativa L.) is a subsistence crop in large areas of Southeast Asia and West Africa which are flooded during the rainy season. Survival of this rice depends on its capacity to elongate rapidly when it becomes partially submerged and to keep part of its foliage above the rising waters. In previous work, these investigators have reconstructed the chain of events that leads from submergence to accelerated growth. They have shown that the initial signal for elongation is the reduced partial pressure of oxygen in the submerged internode and that three plant hormones -- ethylene, abscisic acid, and gibberellin -- participate in regulating growth. Reduced oxygen tensions promotes ethylene synthesis; ethylene causes a reduction in the level of a growth inhibitor, abscisic acid; gibberellin is the immediate growth- promoting hormone; the rate of growth may be determined by the balance of endogenous abscisic acid and gibberellin. Internodal elongation is based on increased production of new cells in the intercalary meristem and on enhanced elongation of these newly formed cells. Experiments outlined in this proposal aim at investigating further the mode of action of ethylene and gibberellin and at studying biochemical and molecular reactions that underlie enhanced cell elongation and increased cell division activity. This research may advance our understanding of plant growth in general and may be important for the eventual transfer of elongation capacity from low-yielding deepwater rice to high- yielding rice cultivars. ***
