Ion Relations of Plants Under Drought and Salinity

Abstract

The review is primarily concerned with the ion relations of mature leaf cells of plants growing under saline conditions: during drought ions do not play such an important role in osmotic adjustment as in salinity. We conclude that, for succulent halophytes (Suaeda maritima), the demand for osmotic adjustment in the leaves matches closely (perhaps exceeds) the supply from the roots. Expanding leaves accumulate sodium at a greater rate than expanded leaves and apoplastic salt concentrations do not exceed those in the protoplast. For salt-sensitive species (Oryza sativa) supply exceeds demand, resulting in a sustained rate of xylem delivery of sodium to the expanded leaves. This in turn leads to either excessive apoplastic ion concentrations in the leaves and death through dehydration or excessive symplastic concentrations and death through ion toxicity.