Carotenoids in the eyespot apparatus of the flagellate green alga Spermatozopsis similis: Adaptation to the retinal-based photoreceptor |
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Authors: | Merete Grung Georg Kreimer Michael Calenberg Michael Melkonian Synnøve Liaaen-Jensen |
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Institution: | (1) University of Trondheim, Norwegian Institute of Technology, Organic Chemistry Laboratories, N-7034 Trondheim-NTH, Norway;(2) Universität zu Köln, Botanisches Institut, Lehrstuhl I, Gyrhofstr. 15, D-50923 Köln, Germany |
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Abstract: | Isolated intact eyespot apparatuses, the photoreceptive organelles involved in blue-light-mediated photoresponses of flagellate green algae, were analyzed regarding their carotenoid composition. Carotenoids from the eyespot apparatuses of Spermatozopsis similis were identified by high-performance liquid chromatography, visible-light absorption spectra, mass spectroscopy and by 1H-nuclear magnetic resonance spectroscopy (carotenes), and compared with those of whole-cell extracts. Both extracts contained , -carotene, , -carotene (formerly -carotene), lycopene, lutein, zeaxanthin, violaxanthin and all-E-and 9 -Z-neoxanthin. The relative carotenoid compositions, however, differed significantly. A twofold relative increase in the total carotene level was evident in the fraction enriched in eyespot apparatuses. This was mainly due to an increase in the monocyclic , -carotene and the aliphatic lycopene, whereas the relative content of , -carotene remained unchanged. On the other hand a relative decrease in the total xanthophyll content, especially of lutein and the epoxidic carotenoid neoxanthin, was observed in the eyespot apparatuses compared with the whole-cell extracts. The decrease of the latter resulted almost solely from a reduction of the 9 -Z-rather than the all-E-isomer. The bulk of the carotenes is thought to be localized in the highly organized eyespot lipid globules, which act as a combined quarter-wave interference reflector and absorption screen for the photoreceptor in green algae. The enrichment of , -carotene and lycopene in the eyespot apparatuses, extending the range of visible light absorption to longer wavelengths, represents an adaptation of the screen to the retinal-based photoreceptor of flagellate green algae and is one of the prerequisites for maximal directional sensitivity of the eyespot apparatus.Abbreviations
1H-NMR
nuclear magnetic resonance
- IUPAC
International Union of Pure and Applied Chemistry
- VIS
visible absorption spectra
This work was supported by the Deutsche Forschungsgemeinschaft (G.K. and M.M.). M.G. was supported by a fellowship from the Norwegian Research Council of Science and Humanities. |
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Keywords: | Carotenoid Eyespot apparatus Green algae Phototaxis Photoreceptor screen Spermatozopsis |
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