On the role of beta-carotene in the reaction center chlorophyll a antennae of photosystem 1 [absorption spectra, low-temperature fluorescence emission spectra, Pisum sativum, photoprotection, photosynthetic mutants, SAN-9789, Scenedesmus obliquus, Triticum aestivum]
1980
Oequist, G. | Samuelsson, G. | Bishop, N.I. (Umeaa Univ. (Sweden). Dept. of Plant Physiology)
Absorption and low temperature fluorescence emission spectra were measured on chloroplast thylakoids and on purified reaction center chlorophyll alpha-protein complexes of photosystem I, CP-a(, I). A clear association between the presence of Beta-carotene and the occurrence of far red absorbing and emitting chlorophyll a components of the reaction center antennae of photosystem I was demonstrated. For this study chloroplasts and CP-a(, I) were obtained from normal and carotenoid deficient plant material of various sources. The experimental material included (1) lyophilized pea chloroplasts extracted with petroleum ether, (2) the carotenoid deficient mutant C-6E of Scenedesmus obliquus and (3) wheat chloroplasts derived from normal and SAN-9789 treated plants. Removal of carotenoids, most likely principally Beta-carotene, caused a loss of long wavelength absorbing chlorophylls in chloroplasts and purified CP-a(I) and the loss or diminution of the long wavelength peak seen in the low temperature fluorescence emission spectrum. This association between Beta-carotene and special chlorophyll a forms may explain both the photoprotective and antenna functions ascribed to Beta-carotene. In the absence of carotenoids in wheat and in the Scenedesmus mutant, the chlorophyll a antenna of photosystem I was extremely photosensitive. A triplet-triplet resonance energy transfer from chlorophyll a to Beta-carotene and a singlet-singlet energy transfer from excited Beta-carotene to chlorophyll would explain the photoprotective and antenna functions, respectively. The role of this association in determining some of the fluorescence properties of photosystem I is also discussed
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