Most rice varieties are grown in flooded fields. Deepwater rice varieties are grown in areas where water levels rise even more during the rainy season. In these plants, partial submergence induces rapid growth of the stem. In this way, deepwater rice plants manage to keep part of their leaves above the rising water level and to supply the submerged plant parts with oxygen. Growth induction is mediated by ethylene.
Ethylene has a very low diffusion rate in water and accumulates in submerged plant parts.
In addition to limited diffusion from the plant, ethylene synthesis is induced by submergence. Both, ACC synthase and ACC oxidase activities increase as a result of low oxygen tension. Ethylene, in turn, increases gibberellin synthesis and sensitivity of the tissue towards gibberellin. Physiologically effective concentrations of gibberellin are ultimately responsible for growth induction in the internode of the rice stem. Growth rates of up to 25 cm per day are achieved through an approximately threefold higher rate of cell division and through increased cell elongation including threefold longer cells.