Automatic Recordings of Action Spectra for Partial Reactions of Photosynthesis

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Abstract
Methods for automatic recordings of action spectra for partial reactions of photosynthesis are previously described. The present paper elaborates one of the descriptions and gives results from measurements. The method is based upon the recordings of changes in the absorption of certain dyes, which are used as electron acceptors or electron donors to photosynthetic reactions in illuminated chloroplasts or photosynthetic lamellae. By measuring the transmission changes continuously during a wavelength sweep of actinic light, which is corrected for equal numbers of light quanta at different wavelengths, an approximate integrated action spectrum of the selected partial reaction is obtained. A computer program gives the action spectrum after taking the first derivative of the curve and correcting it for changes with time in the rate of the dye reduction (oxidation) and the reverse reactions.The action spectrum for photoreduction of 2,6‐dichlorophenol indophenol and cytochrome c by spinach chloroplasts has a peak at about the same wavelength as the absorption spectrum (677–680 nm). Details in the curves are observed at 650, 663, 673 and possibly at 695 nm. The action spectrum for mammalian cytochrome c oxidation by PSI particles of Anacystis nidulans has a peak at 683 nm (absorption spectrum at 679 nm). Shoulders are observed at 665, 677, 700, and 715 nm.

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