Kinetics and Energetics of Light-enhanced Potassium Absorption by Corn Leaf Tissue

The effect of illumination on the absorption of K(+) by leaf tissue of Zea mays was investigated. The rate of K(+) absorption was enhanced by exposure of slices of corn leaf tissue to light, even of relatively low intensities. Potassium was transported inward, with virtually no efflux of previously accumulated K(+). The evidence indicates that the transport mechanism for absorption of K(+) is the same in the light as in the dark, but that the source of energy for absorption of K(+) is different in the light from that in the dark. Various anti-metabolites were used to establish that the energy utilized for active ion transport in the light came partly from ATP supplied by cyclic photophosphorylation. Expenditure of ATP was required in the dark too, but this ATP was formed by oxidative phosphorylation. Establishing the ultimate source of energy for active ion uptake by higher plants might be facilitated by demonstration of an ion-transport process that is not linked directly with the transfer of electrons in the mitochondrial cytochrome chain.