Plant adaptations to anaerobic stress

Inundation that gives rise to soil flooding, or more complete submergence, is the most common environmental cause of oxygen deprivation for vascular plants. Species differ considerably in their susceptibility to the stress. Tolerance can vary from only a few hours to many days or weeks depending on species, the organs directly affected, stage of development, and external conditions such as temperature. Mechanisms that underlie short- and long-term tolerance to external anaerobic conditions are reviewed. For roots, these include metabolic adaptations such as avoidance of self poisoning and cytoplasmic acidosis, maintenance of adequate supplies of energy and sugar, modifications to gene expression and metabolic acclimation to tissue anoxia by previous exposure to partial oxygen shortage. Morphological escape mechanisms based on aerenchyma development and internal aeration pathways are emphasised. Shoots are often less susceptible to oxygen deficiency than roots. Their mechanisms of tolerance can include metabolic adaptations and developmentally passive tolerance such as that seen in overwintering rhizomes of many wetland species. Escape mechanisms for shoots are based on active and, sometimes, increasingly rapid shoot extension in the presence or absence of oxygen, and formation of replacement roots through adventitious rooting at the shoot base. Systemic signalling between roots and shoots integrates root and shoot physiology and limits indirect damage to shoot tissues by soil flooding. The review is completed by an assessment of prospects for future research. (C) 1997 Annals of Botany Company