Orientation of Carotenoid Molecules in the Eyespot of Alga: In Situ Polarized Resonance Raman Spectroscopy

Abstract

Raman spectra of single cells of Euglena and Chlamydomonas have been examined with 514.5 nm excitation at various points within the cells. At every point, two strong bands, which are assignable to carotenoid, appeared at 1530 and 1159 cm⁻¹. By the use of a Raman mapping system, the Raman intensity at 1530 cm⁻¹ has been plotted against the (x,y) coordinate representing a location within the cell. It has been shown that, for both algae examined, the eyespot has a prominently high carotenoid content, and a small amount of carotenoid is uniformly distributed among the chloroplast. The spatial resolution of the mapping system has been shown to be higher than 1 μm, and the Chlamydomonas eyespot has an elongated shape of 1 μm × 2 μm. By use of a polarizer, the carotenoid chains in the Chlamydomonas eyespot have been found to be aligned along its long axis, which is parallel to the body axis.