Physiological and cellular aspects of phytotoxicity tolerance in plants: the role of membrane transporters and implications for crop breeding for waterlogging tolerance

Waterlogging affects large areas of agricultural land, resulting in severe economic penalties because of massive losses in crop production. Traditionally, plant breeding for waterlogging tolerance has been based on the field assessment of a range of agronomic and morphological characteristics. This review argues for a need to move towards more physiologically based approaches by targeting specific cellular mechanisms underling key components of waterlogging tolerance in plants. Also, while the main focus of researchers was predominantly on plant anoxia tolerance, less attention was given to plant tolerance to phytotoxins under waterlogged conditions. This paper reviews the production of major elemental and organic phytotoxins in waterlogged soils and describes their adverse effects on plant performance. The critical role of plasma membrane transporters in plant tolerance to secondary metabolite toxicity is highlighted, and ionic mechanisms mediating the this tolerance are discussed. A causal link between the secondary metaboliteinduced disturbances to cell ionic homeostasis and programmed cell death is discussed, and a new ethylene-independent pathway for aerenchyma formation is put forward. It is concluded that plant breeding for waterlogging tolerance may significantly benefit from targeting mechanisms of tolerance to phytotoxins.