Hypoxia and Anoxia Stress: Plant responses and tolerance mechanisms

Oxygen is a limiting factor for plant growth and development under submerged and waterlogged conditions. Plants are subjected to a varying range of oxygen concentrations, such as normoxia, hypoxia and anoxia which may differ over time and space. To endure oxygen deprivation, plants have evolved a series of morphological and anatomical adaptations, which have been extensively studied. However, metabolic reactions and molecular regulation under oxygen deprivation are not well understood. A comprehensive understanding of how plants respond to oxygen deficiency for stress tolerance and integrated approaches are imperative for developing anoxia and hypoxia tolerant varieties for the flood-prone and waterlogged areas. In this review, adaptations and recent advances in biochemical and molecular approaches during oxygen deprivation have been discussed. Acquiring tolerance against anoxia and hypoxia is an active process consuming a considerable amount of plant resources for the functional maintenance of post-anoxia escape strategies. Understanding of biochemical and molecular mechanisms may help devise contemporary molecular and traditional breeding approaches, and management strategies to improve anoxia-hypoxia tolerance in crop plants.