Journal Article

Light-Induced Dynamic Changes of NADPH Fluorescence in <i>Synechocystis</i> PCC 6803 and Its <i>ndhB</i>-Defective Mutant M55

Hualing Mi, Christof Klughammer and Ulrich Schreiber

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 41, issue 10, pages 1129-1135
Published in print October 2000 | ISSN: 0032-0781
Published online October 2000 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcd038
Light-Induced Dynamic Changes of NADPH Fluorescence in Synechocystis PCC 6803 and Its ndhB-Defective Mutant M55

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Blue-green fluorescence emission of intact cells of Synechocystis PCC6803 and of its ndhB-defective mutant M55 was measured with a standard pulse-amplitude-modulation chlorophyll fluorometer equipped with a new type of emitter-detector unit featuring pulse-modulated UV-A measuring light and a photomultiplier detector. A special illumination program of repetitive saturating light pulses with intermittent dark periods (10 s light, 40 s dark) was applied to elicit dynamic fluorescence changes under conditions of quasi-stationary illumination. The observed effects of artificial electron acceptors and inhibitors on the responses of wild-type and mutant M55 cells lead to the conclusion that changes of NAD(P)H fluorescence are measured. In control samples, a rapid phase of light-driven NADP reduction is overlapped by a somewhat slower phase of NADPH oxidation which is suppressed by iodoacetic acid and, hence, appears to reflect NADPH oxidation by the Calvin cycle. Mercury chloride transforms the light-driven positive response into a negative one, suggesting that inhibition of NADP reduction at the acceptor side of PSI leads to reduction of molecular oxygen, with the hydrogen peroxide formed (via superoxide) causing rapid oxidation of NADPH. The new fluorescence approach opens the way for new insights into the complex interactions between photosynthetic and respiratory pathways in cyanobacteria.

Keywords: Key words: Cyclic photosystem I — Hydrogen peroxide — NADPH dehydrogenase — NADPH fluorescence — Respiration — Synechocystis PCC 6803.; Abbreviations: DBMIB, 2,5-dibromo-3-methyl-isopropyl-p-benzoquinone; FNR, ferredoxin-NADP+ oxidoreductase; IAA, iodoacetic acid; LED, light emitting diode; NDH, NADPH dehydrogenase; PAM, pulse-amplitude-modulation.

Journal Article.  4578 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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