GLOEOBACTER VIOLACEUS - INVESTIGATION OF AN UNUSUAL PHOTOSYNTHETIC APPARATUS - ABSENCE OF THE LONG-WAVELENGTH EMISSION OF PHOTOSYSTEM-I IN 77 K FLUORESCENCE-SPECTRA

The deeply purple cyanobacterium Gloeobacter violaceus is subject of t his investigation. It does not contain thylakoids, and the photosynthe tic apparatus is located in the only membrane of the cell, the plasma membrane. Upon excitation with blue light, the 77 K fluorescence emiss ion spectra of neither intact cells (excited with 427 nm) nor of the i solated plasma membrane (excited with 430 nm), show the expected long wavelength photosystem I emission characteristic for low energy chloro phylls. Maximal fluorescence emission was observed at 688 nm, independ ent on the excitation wavelength, 427 (430) nm blue light, exciting ma inly chlorophyll, or 550 nm green light, exciting mainly phycoerythin. The ratio of P700 to chlorophyll was 175. O-2-evolution was 160 mu mo l mg(-1) chlorophyll h(-1) in saturating while light; the compensation point was reached at 6 mu mol m(-2) s(-1) in cultures grown at 25 mu mol m(-2) s(-1). Dark O-2 uptake was 50 mu mol mg(-1) chlorophyll h(-1 ). During adaptation to increasing white light intensities Gloeobacter reduces the amount of phycocyanin and chlorophyll per cell and strong ly increases the concentration of carotenoids relative to chlorophyll. The carotenoid concentration per cell increases with increasing light intensity. Apparently, part of the carotenoids is not located in the plasma membrane.