The salinity challenge and sodium toxicity The two major environmental factors which currently Cells respond to salt stress by osmolyte synthesis and by increase of K+ uptake and Na+ efflux at the plasma reduce plant productivity are drought and salinity. For example, disease and insect losses, while often devastating membrane and of Na+ accumulation at the vacuole. This cellular level of response has been approached to individual farmers, depress yields on the average by less than 10%, while unfavourable physicochemical envir-