ASPECTS OF PLANT BEHAVIOR UNDER ANOXIA AND POSTANOXIA

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