ACTION SPECTRA FOR PHOTOSYNTHESIS AND LIGHT‐STIMULATED ION TRANSPORT PROCESSES IN HYDRODICTYON AFRICANUM

Abstract

SummaryThe action spectra in the wavelength range 436–759 nm of photosynthesis and light‐dependent ion transport processes in Hydrodictyon africanum were determined. The action spectra for active Cl influx and the associated components of K and Na influx, and the passive K efflux and the passive component of K influx, all had action spectra very similar to that of photosynthesis. These processes are stimulated by light absorbed by the photosynthetic system, and require photosystem 2. Active K influx and the coupled Na efflux, on the other hand, do not show such a pronounced drop in the action spectrum above 680 nm as does photosynthesis; below 680 nm the action spectrum is very similar to that of photosynthesis. This cation regulation mechanism thus only needs photosystem I. The results obtained above 680 nm confirm and extend those previously obtained with cut‐off filters (Raven, 1967b).The Emerson enhancement effect was exhibited by photosynthesis but not by Cl influx. The absence of enhancement of Cl influx could not be explained by a de‐enhancing action of photochrome at the wavelengths used. This absence of enhancement, if genuine, implies that only photosystem 2 is needed for light‐stimulation of Cl influx.No evidence was found for participation of the blue pigment or of phytochrome in any of the processes studied.