XVI International Botanical Congess

Gas diffusion is severely inhibited in flooded soils resulting in a hypoxic or anoxic sediment in which availability of nutrients for plants strongly decreases. The first anaerobic process to occur is the reduction of nitrate to nitrogen or ammonium ions, followed by the reduction of manganese, ferric oxides and sulfate. Within the plant, flooding induces major changes in the concentration of O2, CO2 and ethylene. Submerged plants that are able to photosynthesize at reduced CO2 levels and to reduce their respiratory rate have a great advantage. Long-term responses are the development of aerenchyma and new adventitious roots. If leaves emerge from the water surface, downward supply of O2 and, in reverse, CO2 and ethylene occur. Increased ethylene concentration is largely responsible for promoting fast extension under water. A gene responsible for ethylene perception was recently isolated in Rumex palustris. The transcript levels of this gene increase during submergence and also during exposure to high concentrations of ethylene and low concentrations of oxygen. This strongly suggests a correlation between ethylene receptor expression and ethylene-driven shoot elongation.