Plant adjustment to osmotic stress in balanced mineral-nutrient media

Abstract

Studies of salt tolerance of plants grown in balanced nutrient solutions revealed that growth rate was more a function of the duration of the applied stress than the rapidity with which a particular osmotic concentration was reached in the root medium.The low osmotic potentials initially attained by plants subjected to osmotic stress resulted from both a decrease in water content and an increase in ion concentration in the plant tissues. However, the importance of dehydration in the adjustment process decreased within a relatively short time, and ion uptake was noted to be the predominant factor in the adjustment of the plant sap throughout the vegetative period. With the exception of restrictions on growth, symptoms of ion toxicity were not observed with these balanced solutions, although exposure to stress in one of the treatment series lasted for 84 days.Substantial increases in osmotic potential on the removal of stress were apparently the result of passive diffusion of ions back to the substrate, rather than an increase in the water content of the tissues as previously reported. The cations K+ and Ca2+ provided the major contribution to changes in the osmotic potential of the foliar sap, but significant changes were noted in all of the ions measured.