Dark adaptation and conformations of carotenoids in the cells of Cladophora aegagropila (L). Rabenh.

Abstract

Intact cells of freshwater algae Cladophora aegagropila (L). Rabenh. (synonymous to Aegagropila linnaei Kutz.) were investigated by resonance Raman spectroscopy. It was found that incubation in the dark (up to 24 h) leads to changes in the Raman spectroscopy spectrum of this species, namely to changes in the ratio of amplitudes of the I₁₅₂₃/I₁₁₅₅ and I₉₆₀/I₁₀₀₄ bands and in the half width of band in the region of 1523 cm–1. We suggested that the adaptation of algae to the dark alters the conformation of the molecule of the carotenoid by delocalization of π-electrons in the polyene chain of the molecule and changes the orientation of the ring. Moreover, the composition of carotenoids, as well as their location in the cell and microenvironment in the pigment–protein complexes can change: in the absence of illumination, the distribution of carotenoids in algal cells is more uniform. These changes are probably caused either by changes in the location of cell organelles or by carotenoid redistribution between photosynthetic membranes, plastoglobules, and lipophilic formations in the cytoplasm.