Fluorescence of chlorophyll in photosynthetic systems III. Emission and action spectra of fluorescence—Three emission bands of chlorophyll a and the energy transfer between two pigment systems

The emission and action spectra of fluorescence of photosynthetic pigments, especially of chlorophyll a, were studied in spinach chloroplasts, Anacystis nidulans, Porphyra yeroensis, Porphyridium cruentum and other photosynthesis organisms at −196°, to elucidate the behavior of the pigments in fluorescence and energy transfer. At −196°, in most of the materials used, three emission bands of chlorophyll a were observed at 684 mμ, 695 mμ and 710–735 mμ (designated as F684, F695 and F-1). The emission and action spectra showed that F684 and F695 were excited by the light absorbed by phycobilins or chlorophyll b (pigment system II) and were excited less effectively, or not at all, by the light absorbed by chlorophyll a (pigment system I). F-1 was excited by both wavelenght regions. The light absorbed by pigment system I was more effective for F-1 than for F684 and F695, and the light absorbed by pigment system II was more effective for F684 and F695 than for F-1. A quantum yield of fluorescence as high as 0.75 was obtained in spinach chloroplasts at −196°. At this temperature, F-1 amounted to approx. three-quarters of the total quanta emitted, even upon excitation by 475-mμ light. It was concluded that two forms of chlorophyll a emitting F684 and F695 are contained in pigment system II, while F-1 is involved in pigment system I. Energy is transferred from pigment system II to I, at least at −196°, and presumbly also at physiological temperatures.