Wavelength-Dependent Optical Response of Single Photosynthetic Antenna Complexes from Siphonous Green Alga Codium fragile.

The siphonaxanthin-siphonein-Chl-a/b-protein (SCP) complex from the siphonous green alga Codium fragile is the major light-harvesting complex (LHC) of these alga and is highly homologous to that of green plants (trimeric pigment-protein complex, LHCII). Interestingly, we find remarkable differences in the spectral response from individual SCP complexes when excited at 561 and 639 nm. While excitation in the green spectral range reproduces the common LHCII-like emission features for most of the complexes, excitation in the red spectral range yields a red-shifted emission and a significant reduction of the fluorescence decay time. We hypothesize that the difference in spectral response of SCP to light in the green and red spectral ranges can be associated with the adaption of the algae to their natural habitat under water, where sudden intensity changes are diminished, and excess light features a red-enhanced spectrum that comes at tidal timings.