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Published on August 6, 2004; 10.1104/pp.104.045963

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Received May 8, 2004
Returned for revision June 9, 2004
Accepted June 9, 2004

Traffic Lights in Trichodesmium. Regulation of Photosynthesis for Nitrogen Fixation Studied by Chlorophyll Fluorescence Kinetic Microscopy

Hendrik Küpper *, Naila Ferimazova , Ivan Setlík , and Ilana Berman-Frank

Mathematisch-Naturwissenschaftliche Sektion, Fachbereich Biologie, Universität Konstanz, D-78457 Konstanz, Germany (H.K.); Faculty of Biological Sciences and Institute of Physical Biology, University of South Bohemia, CZ-370 05 Ceske Budejovice, Czech Republic (H.K., N.F., I.S.); Institute of Microbiology, Department of Autotrophic Microorganisms, Academy of Sciences of the Czech Republic, CZ-37981 Trebon, Czech Republic (N.F., I.S.); and Faculty of Life Sciences, Bar Ilan University, Ramat Gan 52900, Israel (I.B.-F.)

* Corresponding author; email: hk282{at}cornell.edu.

We investigated interactions between photosynthesis and nitrogen fixation in the non-heterocystous marine cyanobacterium Trichodesmium IMS101 at the single-cell level by two-dimensional (imaging) microscopic measurements of chlorophyll fluorescence kinetics. Nitrogen fixation was closely associated with the appearance of cells with high basic fluorescence yield (F0), termed bright cells. In cultures aerated with normal air, both nitrogen fixation and bright cells appeared in the middle of the light phase. In cultures aerated with 5% oxygen, both processes occurred at a low level throughout most of the day. Under 50% oxygen, nitrogen fixation commenced at the beginning of the light phase but declined soon afterwards. Rapid reversible switches between fluorescence levels were observed, which indicated that the elevated F0 of the bright cells originates from reversible uncoupling of the photosystem II (PSII) antenna from the PSII reaction center. Two physiologically distinct types of bright cells were observed. Type I had about double F0 compared to the normal F0 in the dark phase and a PSII activity, measured as variable fluorescence (Fv = Fm - F0), similar to normal non-diazotrophic cells. Correlation of type I cells with nitrogen fixation, oxygen concentration, and light suggests that this physiological state is connected to an up-regulation of the Mehler reaction, resulting in oxygen consumption despite functional PSII. Type II cells had more than three times the normal F0 and hardly any PSII activity measurable by variable fluorescence. They did not occur under low-oxygen concentrations, but appeared under high-oxygen levels outside the diazotrophic period, suggesting that this state represents a reaction to oxidative stress not necessarily connected to nitrogen fixation. In addition to the two high-fluorescence states, cells were observed to reversibly enter a low-fluorescence state. This occurred mainly after a cell went through its bright phase and may represent a fluorescence-quenching recovery phase.




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[Abstract] [Full Text] [PDF]


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