Carotenoids in the eyespot apparatus of the flagellate green algaSpermatozopsis similis: Adaptation to the retinal-based photoreceptor
✍ Scribed by Merete Grung; Georg Kreimer; Michael Calenberg; Michael Melkonian; Synnøve Liaaen-Jensen
- Book ID
- 104657661
- Publisher
- Springer-Verlag
- Year
- 1994
- Tongue
- English
- Weight
- 602 KB
- Volume
- 193
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
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 fl,fl-carotene, fl, O-carotene (formerly 7-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 fl,~9-carotene and the aliphatic lycopene, whereas the relative content of fl,fl-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 offl,~-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.