Multiphasic uptake of potassium by corn roots: no linear component.

Concentration-dependence data (LV Kochian, WJ Lucas Plant Physiol 1982 70: 1723-1731; [1983] 73: 208-215; [1985] 429-436; LV Kochian, J Xin-zhi, WJ Lucas [1985], 79: 771-776) for potassium uptake by corn roots have been claimed to be resolvable into a saturable and a linear component representing two separate uptake mechanisms. A comprehensive analysis shows, however, that the data are not compatible with this concept. They can, in contrast, be precisely represented by multiphasic isotherms, in agreement with many findings for uptake of potassium and other solutes. Solute uptake in plants is proposed to be mediated by multistate entities having carrier-like properties at low external solute concentrations and channel-like properties at high concentrations.