Salinity stress: physiological constraints and adaptive mechanisms.

A significant part of the world's land area is salt-affected. Most crops are not able to handle large amounts of salt without a negative impact on their growth and metabolism, so understanding the physiological mechanisms by which plants deal with salinity is essential to minimize detrimental effects and reduce the multibillion dollar penalties imposed by salt stress on crop production. This chapter summarizes our current knowledge of physiological mechanisms conferring plant adaptive responses to salinity. The classification of saline soils is given, with causes of primary and secondary types of salinity. Major physiological constraints are then summarized, and physiological and genetic diversity of plant responses to salinity are discussed. Key physiological and anatomical mechanisms conferring salinity tolerance in plants are then analysed in detail, and practical ways of ameliorating salinity stress are considered. Altogether, this chapter shows that plants have evolved numerous mechanisms to prevent accumulation of toxic Na+ levels in cell cytosol. This ability is complemented by mechanisms enabling efficient osmotic adjustment and maintenance of the cell turgor, as well as mechanisms of coping with oxidative stress imposed by salinity. A more complete physiological and genetic understanding of these processes will enable breeders to produce new salt-tolerant plants for the future.