PHOTOSYNTHETIC LIGHT-HARVESTING FUNCTION OF VIOLAXANTHIN IN NANNOCHLOROPSIS SPP. (EUSTIGMATOPHYCEAE)1 |
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Authors: | Thomas G Owens Jane C Gallagher Randall S Alberte |
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Institution: | 1. Department of Molecular Genetics and Cell Biology, Barnes Laboratory, The University of Chicago, 5630 S. Ingleside Ave. Chicago, Illinois 60637;2. Biology Department and Institute of Marine and Atmospheric Sciences, City College of the City University of New York Covent Ave. at 138th Street, New York, New York 10031;3. Department of Molecular Genetics and Cell Biology, Barnes Laboratory, The University of Chicago, 5630 S. Ingleside Ave. Chicago, Illinois 60637
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Abstract: | Whole cell absorption spectra of the Eustigmatophycean algae Nannochloropsis salina Bourrelly and Nannochloropsis sp. reveal the presence of a distinct absorption peak at 490 nm. The lack of chlorophylls b and c in these species indicates that this peak must be attributed to carotenoid absorption. In vivo fluorescence excitation spectra for chlorophyll a emission show a corresponding maximum at 490 nm. This peak is more clearly resolved than carotenoid maxima in other algal classes due to the absence of accessory chlorophylls. The carotenoid composition of the two Nannochloropsis species shows that violaxanthin and vaucheriaxanthin are the main contributors to 490 nm absorption. Violaxanthin accounts for approximately 60% of the total carotenoid in both clones. We conclude that light absorption by violaxanthin, and possibly by vaucheriaxanthin, is coupled in energy transfer to chlorophyll a and that violaxanthin is the major light-harvesting pigment in the Eustigmatophyceae. This is the first report of the photosynthetic light-harvesting function of this carotenoid. |
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Keywords: | carotenoids energy transfer Eustigmatophyceae fluorescence photosynthesis violaxanthin |
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