Effect of calcium on the potassium flux into the exudate of excised maize roots.

The effect of varying calcium concentration in the medium on the potassium flux into the exudate has been studied. In media of low ionic strength (o.1 mM KCl) the potassium flux, J K, was significantly increased by increasing the calcium concentration of the medium. But in higher ionic strength media (10 mM) KCl) there was no increase in J K as the calcium concentration of the medium was increased. The effect of external sodium concentration on J K was also studied. These results are discussed in relation to present theories of salt and water movement into the plant root. It is concluded that two pathways potentially exist for movement of salts to the exudate stream: firstly, via a symplasm and secondly, through the cell wall pathway. But is is further concluded that the cell wall pathway, at normal physiological ionic strengths, is not available for salt transport due to co-ion exclusion by the fixed negative charges.