Flooding and low oxygen responses in plants.

The world is currently experiencing dramatic increases in flood events impacting on natural vegetation and crops. Flooding often results in low O2 status in root tissues during waterlogging, but sometimes also in shoot tissues when plants become completely submerged. Plants possess a suite of traits enabling tissue aeration and/or adjusted metabolism during hypoxia or even in the absence of O2. This special issue of Functional Plant Biology presents key papers for plant scientists on the quest to further address and improve flood tolerance of terrestrial plants. The papers address low O2 responses in roots, shoots or whole plants in controlled laboratory conditions or in the field situation using natural wetland plants as models as well as economically important crops, such as rice, wheat and barley. The studies advance our understanding of low O2 responses in plant tissues as caused by O2 shortage during flooding. However, in most instances, submergence not only leads to hypoxic or anoxic tissues, but inundation in water also results in accumulation of CO2 and the important plant hormone ethylene. Thus, carefully designed laboratory studies are often needed to unravel the mechanistic relationships between a combined decline in O2 followed by increases in CO2 and ethylene at tissue as well as on the cellular level.