CHROMATIC ADAPTATION AND THE EVENTS INVOLVED IN PHYCOBILISOME BIOSYNTHESIS

Abstract. The major light‐harvesting complex in cyanobacteria and red algae is the phycobilisome, a macromolecular complex that is attached to the surface of the photosynthetic membranes. The phycobilisome is composed of a number of different chromophoric polypeptides called phycobiliproteins and nonchromophoric polypeptides called linker proteins. Several environmental parameters modulate the synthesis, assembly and degradation of phycobilisome components. In many cyanobacteria, the composition of the phycobilisome can change to accommodate the prevalent wavelengths of light in the environment. This phenomenon is called complementary chromatic adaptation. Organisms that exhibit complementary chromatic adaptation must perceive the wavelengths of light in the environment and transduce the light signals into a sequence of biochemical events that result in altering the activities of genes encoding specific phycobiliprotein and linker polypeptides. Other environmental parameters such as light intensity and nutrient status can also have marked effects on both the number and composition of the phycobilisomes. The major concern of this article is the molecular events involved in chromatic adaptation. Most of the information concerning this process has been gained from studies involving the filamentous cyanobacterium Fremyella diplosiphon. However, also briefly considered are some of the complexities involved in phycobilisome biosynthesis and degradation; they include post‐translational modification of phycobilisome polypeptides, the coordinate expression of chromophore and apobiliprotein, the specific degradation of phycobilisomes when cyanobacteria are deprived of macronutrients such as nitrogen, sulphur and phosphorus, and the assembly of the individual phycobilisome components into substructures of the light harvesting complex. Copyright © 1990, Wiley Blackwell. All rights reserved