Mechanisms of waterlogging tolerance in wheat: Morphological and metabolic adaptations under hypoxia or anoxia

Waterlogging is a widespread limiting factor for wheat production throughout the world specially irrigated and high rainfall environments. The important biological consequence of waterlogging is the deficiency (hypoxia) or complete absence (anoxia) of oxygen in soil environment which restricts the growth, development and finally yield in wheat. The tolerant genotypes of wheat can adapt to transient waterlogging by developing mechanisms related to morphology and metabolism to cope with the stress. The morphological mechanisms include the development of adventurous roots with well formed aerenchyma and sometimes with a barrier for ROL. Aerenchyma is a continuous gas filled channel, which provides a low resistance internal pathway for the movement of O2 from the aerobic shoots to anaerobic roots to respire aerobically under hypoxia or anoxia. However, lack of oxygen induces the anaerobic roots to shift the energy metabolism from aerobic to anaerobic mode. Greater activities of glycolytic and fermentative enzymes, increased availability of soluble sugars, and involvement of antioxidant defense mechanism against post-stress oxidative damages are the main metabolic mechanisms for waterlogging tolerance in wheat.