ASPECTS OF PLANT BEHAVIOR UNDER ANOXIA AND POSTANOXIA

All plants are able to survive anoxic periods, but the degree of toler ance shows large variation. The main injuries related to anoxia are ev entually due to changes in energy metabolism. Low energy charge values indicate a cessation of many ATP consuming processes. Sugar starvatio n, lactic acid fermentation and proton release from leaky vacuoles are responsible for cell death. Long-term anoxia tolerance is dependent o n storage products in the vicinity of sinks, on an adequate control of glycolysis, synthesis of essential proteins, and stability of membran es and organelles. However, no fundamental differences between the met abolic pathways of tolerant and non-tolerant tissues are known. It is rather a question of minor changes and the regulation of anaerobic met abolism. Re-exposure of anoxic tissues to air may even be more detrime ntal than anoxia itself. These injuries are mainly due to enhanced rad ical generation. Lipid peroxidation processes lead to membrane damage, disintegration, and leakage of solutes. Under natural conditions plan ts are equipped with radical-detoxifying systems (SOD, peroxidases and antioxidants). Natural detoxifying systems can be reduced in non-adap ted plants under anoxia and they become more sensitive to post-anoxic damage. In addition, the rapid conversion of ethanol to extremely toxi c acetaldehyde seems to be a cause of tissue injury and death.