The Action Spectrum for the Photochemical Evolution of Oxygen by Isolated Chloroplasts

Abstract

The Hill reaction was followed by the reduction of an oxidation-reduction dye, 2, 6-dichlorophenol indophenol. Samples of the mixture of the dye and chloroplasts were exposed to monochromatic light obtained from a Wood replica grating monochro-mator. The degree of dye reduction produced by exposure was measured with a Beckman spectrophotometer at the wave length corresponding to the absorption peak of the dye. The action spectrum of this reaction was obtained by plotting the effectiveness of light against wave length. This curve was compared with the absorption spectrum of chloroplast suspension and the photosynthetic action spectra of Chlorella and Ulva. Quantum requirement for this reaction was calculated. All findings are consistent with the view that Hill reaction is identical with the primary photochemical step of photosynthesis. The action spectrum of this reaction thus may be interpreted as a measure of the spectrum effectiveness for the photosynthetic process in chlorophasts of a higher plant.