ACTIVE ACCUMULATION OF SODIUM BY ROOTS OF FIVE AQUATIC SPECIES

It is suggested that active accumulation of sodium is evident in plant roots when the external sodium concentration is low, and Ca++ and Mg++ appear to be in electrochemical equilibrium with the external medium.

Abstract

SUMMARY The accumulation of several major nutrient ions by the roots of some aquatic plants was investigated. Five species growing in freshwater lochs on the north coast of Scotland were studied. Electrical potential differences between root epidermal cells and the surrounding loch water were measured using micro‐electrodes. From these measurements, electrochemical potential gradients between the roots and the loch water were calculated, and also the driving forces on each ion. For each species investigated, the results indicate that sodium is actively accumulated by the roots. This contrasts with results of studies which provide evidence for a sodium efflux pump in plant cells. It is suggested that active accumulation of sodium is evident in plant roots when the external sodium concentration is low. The results showed that K + , Cl ‐ , and NO 3 ‐ are actively accumulated; Ca ++ and Mg ++ appear to be in electrochemical equilibrium with the external medium.