Unique properties vs. common themes: the atypical cyanobacterium Gloeobacter violaceus PCC 7421 is capable of state transitions and blue-light-induced fluorescence quenching.
The atypical unicellular cyanobacterium Gloeobacter violaceus PCC 7421, which diverged very early during the evolution of cyanobacteria, can be regarded as a key organism for understanding many structural, functional, regulatory and evolutionary aspects of oxygenic photosynthesis. In the present work, the performance of two basic photosynthetic adaptation/protection mechanisms, common to all other oxygenic photoautrophs, had been challenged in this ancient cyanobacterium which lacks thylakoid membranes: state transitions and non-photochemical fluorescence quenching. Both low temperature fluorescence spectra and room temperature fluorescence transients show that G. violaceus is capable of performing state transitions similar to evolutionarily more recent cyanobacteria, being in state 2 in darkness and in state 1 upon illumination by weak blue or far-red light. Compared with state 2, variable fluorescence yield in state 1 is strongly enhanced (almost 80%), while the functional absorption cross-section of PSII is only increased by 8%. In contrast to weak blue light, which enhances fluorescence yield via state 1 formation, strong blue light reversibly quenches Chl fluorescence in G. violaceus. This strongly suggests regulated heat dissipation which is triggered by the orange carotenoid protein whose presence was directly proven by immunoblotting and mass spectrometry in this primordial cyanobacterium. The results are discussed in the framework of cyanobacterial evolution.
Plant Biochemistry, Ruhr-University Bochum, D-44801 Bochum, Germany. gabor.bernat@rub.de
Gábor
G
Bernát
Ulrich
U
Schreiber
Esther
E
Sendtko
Igor N
IN
Stadnichuk
Sascha
S
Rexroth
Matthias
M
Rögner
Friederike
F
Koenig
D001426:Bacterial Proteins / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D004237:Diuron / Q000494:pharmacology; D007700:Kinetics; D008027:Light; D055668:Photochemical Processes / Q000187:drug effects / Q000528:radiation effects; D013050:Spectrometry, Fluorescence; D013347:Subcellular Fractions / Q000187:drug effects / Q000528:radiation effects; D046939:Synechocystis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D013696:Temperature; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects
D001426:Bacterial Proteins; D002734:Chlorophyll; D004237:Diuron