Water and Solute Transport by Exuding Root Systems ofRicinus communis

Abstract

The influence of range of concentrations of potassium nitrate (C_m)in the medium surrounding the roots of decapitated Ricinus communis plants on: (a) the potassium concentration of the exudate (C_s), (b)the rate of exudation (fH₂O), and (c) the flux of potassium into the exudate (f_k) was investigated. A change in C_m could influence exudation by altering the osmotic potential of the medium as will as by a change in potassium concentration, and these two effect were separated in the following way. the effect of varying the potassium concentration was investigated using media made isotonic with mannitol, whilst the osmotic effect was investigated using mannitol solutions of various concentrations but of equal potassium concentration. An analysis of the results revealed the existence of two salt-transfer processes, one independent of the water flux but dependent on the concentration of potassium in the medium, the other linearly related to the flux of water through the root system. The implications of these findings in relation to the intact transpiring plant are discussed.