The cellular basis of the elongation response in submerged deep-water rice

The cellular basis of internode elongation was studied in intact deep-water rice plants (Oryza sativa L. cv. "Habiganj Aman II") and in isolated stem sections. In intact plants, growth was stimulated by submergence in water and by ethylene treatment. In isolated sections, growth was enhanced by submergence, by ethylene, and by exposure of the tissue to an atmosphere of 3% O2, 91% N2 and 6% CO2 or 3% O2, 91% N2, 6% CO2 and 1 μl l(-1) C2H4 (by vol.). Under all these conditions, growth was localized in the intercalary meristem at the bases of the internodes. Autoradiography of [(3)H]thymidine-labeled tissue showed activation of cell division and longitudinal expansion of the intercalary meristem. Increased production of new cells and their subsequent elongation thus form the basis for the growth response to submergence and ethylene treatment in deep-water rice plants.