Photosynthetic organisms must be able to sense and respond to changes in the ambient light environment for long-term survival. A number of light-dependent physiological responses have been identified including photoperiodism, phototaxis, and photoregulation of the light-harvesting complexes to maximize photosynthesis. A long-recognized light-dependent process that occurs in some cyanobacteria is called complementary chromatic
FLAG Peptide (CCA), which results in changes in the protein composition of the photosynthetic light-harvesting phycobilisome (PBS) complexes of cyanobacterial
cells in response to changes in the ratio of red-to-green wavelengths in the ambient light environment [5] and [7]. In cyanobacteria that exhibit CCA, the PBS of wild-type (WT) cells grown in red light (RL) accumulate high levels of the RL-absorbing phycocyanin (PC) pigment, resulting in cells that have a blue-green color. Conversely, high levels of the green-light (GL)-absorbing phycoerythrin (PE) pigment accumulate under green illumination, leading to cells that are red to brick red in color.
