[34] Complementary chromatic adaptation: Physiological conditions and action spectra

This chapter focuses on the physiological conditions and action spectra of complementary chromatic adaptation. Photosynthetic organisms can modulate their relative pigment content in response to changes in either light intensity or light wavelength. Generally, one observes an inverse correlation between light intensity and pigment content—the less light energy available, the more photosynthetic pigments are synthesized by the cells. The effect of light wavelength on the pigment content of the cells, termed complementary chromatic adaptation, appears to be restricted to some cyanobacteria. In this type of adaptation, changes in cell pigmentation in response to specific spectral illuminations result from modifications of the relative amounts of the red-colored phycoerythrin (PE) and the blue-colored phycocyanin (PC), with a predominance of PE in green-light-grown cells and of PC in red-light-grown cells. The regulatory processes involved in complementary chromatic adaptation are controlled by a photoreceptor pigment system which presumably acts at the transcriptional level. The property of photoreversibility of the cyanobacterial photoreceptor resembles that of the phytochrome present in higher plants and algae, although its action maxima are situated at shorter wavelengths in the visible spectrum.