Light stimulation of active transport in Hydrodictyon africanum.

The mechanism of light stimulation of active K and Cl influx and active Na efflux, in Hydrodictyon africanum has been investigated using different wavelengths of red light and different gas mixtures, and the inhibitors DCMU and CCCP. The active Cl influx requires photosystem 2, since its relative quantal efficiency falls with increasing wavelength of red light, and it is as sensitive to the inhibitor DCMU as is photosynthesis; it is relatively insensitive to the uncoupler CCCP. The active K influx and active Na efflux are inhibited by CCCP, but the relative quantal efficiency of these processes increases with increasing wavelength of red light, and they are relatively insensitive to DCMU. These cation fluxes can be supported by cyclic photophosphorylation, whereas Cl influx needs photosystem 2 but probably not ATP.