Presence of both hemidiscoidal and hemiellipsoidal phycobilisomes in a phormidium species (cyanobacteria)

Abstract

Hemidiscoidal and hemiellipsoidal phycobilisomes have been determined in cells of the complementary chromatically adapting cyanobacterium Phormidium sp. C 86. They could be isolated from red and green light-adapted cells, respectively. Hemidiscoidal red light phycobilisomes show molar pigment ratios o f allophycocyanin: phycocyanin of 1:4.5 with phycoerythrin lacking. Hemiellipsoidal phycobilisomes induced by green light present allophycocyanin: phycocyanin: phycoerythrin ratios of 1:1:6.8. The differences between the two phycobilisome types could additionally be dem onstrated by their ultrastructure and sedimentation values. Isolated red light phycobilisomes have six rods, show dimensions of 70 x 30 x 15 nm and a sedimentation value o f 66 S whereas green light phycobilisomes are nearly twice larger. They contain ten rods and present dimensions of 70 x 40 x 25 nm and a sedimentation value of 98 S. The number of phycobilisomes in red light cells is almost twice as large as in green light cells. There is evidence that cells grown under white light contain both types as well as “intermediate” forms. © 1993, Walter de Gruyter. All rights reserved.