A mathematical analysis of the relationship between the flux of water,/H,O, and the flux of potassium/K, to the xylem of exuding root systems of Ricinus communis, is presented. Previous analyses (Baker and Weatherley, 1969;Minchin and Baker, 1969) have indicated the presence of a water dependent and a water independent fK both of which vary with the external concentration of potassium, Cm, supplied as potassium nitrate.
The present analysis reveals that whereas at Cm values < 1 mM both components of/K contribute ions to the osmotically active solutions within the osmotic barrier, at Cm values > 1 ml~ only the water dependent ]K is responsible for the osmotic work. This suggests that the ions are released within different regions of the stele. It is proposed that at Cm values < 1 ml~ both components are released from the inner stelar tissues whilst at higher Cm values the water dependent/K is released from the outer stelar tissues. This requires that the solute permeability of the plasmalemma of the outer stelar tissues increases markedly at or about Cm values of 1 raM.
It is postulated that the required separation of the two/K components within the stelar symplasm at Cm values > 1 mM is due to the water independent /K being in a bound state, possibly being transported along a chain of binding sites whilst the water dependent/K is in a free state within the aqueous phase of the cytoplasm.