PHOTOREGULATION OF PHYCOBILISOME STRUCTURE DURING COMPLEMENTARY CHROMATIC ADAPTATION IN THE MARINE CYANOPHYTE PHORMIDIUM SP. C861

Abstract

ABSTRACTChanges in the molecular structure of phycobilisomes during complementary chromatic adaptation were studied in the marine cyanophyte Phormidium sp. C86. This strain forms phycoerythrin (PE)‐less phycobilisomes under red light but synthesizes PE‐rich phycobilisomes under green light. Analysis of phycobiliprotein composition and electron microscopic examination of phycobilisomes in ultra‐thin sections of cells and of isolated phycobilisomes were performed for cells acclimated to red and green light, respectively. The structure of phycobilisomes formed under red light conditions was typically hemidiscoidal. Phycobilisomes in cells acclimated to green light were twice as large in size as those in cells acclimated to red light. This increase in phycobilisome size was a result of the increase in the molar ratio of antenna pigment (PE and phycocyanin) to allophycocyanin, from 3.5 to 11.3. Pigment composition and fine structure of phycobilisomes formed under green light were similar to those of “nonhemidiscoidal” phycobilisomes reported in Phormidium persicinum. These results suggest that changes occur not only in the molecular species of peripheral rods but also in the structure of rods and probably of cores in relation to their connection with rods during chromatic adaptation of Phormidium sp. C86.