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On the role of ß‐carotene in the reaction center chlorophyll a antennae of photosystem I
Author(s) -
OQUIST By GUNNAR,
SAMUELSSON GÖRAN,
BISHOP NORMAN I.
Publication year - 1980
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1980.tb02685.x
Subject(s) - light harvesting complexes of green plants , photochemistry , photosystem i , photosynthetic reaction centre , chlorophyll , photosystem ii , chloroplast , p700 , chlorophyll a , chlorophyll fluorescence , chlorophyll b , chemistry , photosynthesis , biology , botany , biochemistry , electron transfer , gene
Absorption and low temperature fluorescence emission spectra were measured on chloroplast thylakoids and on purified reaction center chlorophyll a ‐protein complexes of photosystem I, CP‐a 1 . A clear association between the presence of ß‐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 1 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 ß‐carotene, caused a loss of long wavelength absorbing chlorophylls in chloroplasts and purified CP‐a 1 , and the loss or diminution of the long wavelength peak seen in the low temperature fluorescence emission spectrum. This association between ß‐carotene and special chlorophyll a forms may explain both the photoprotective and antenna functions ascribed to ß‐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 ß‐carotene and a singlet‐singlet energy transfer from excited ß‐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.