Light-induced and osmotically-induced changes in chlorophyll a fluorescence in two Synechocystis sp. PCC 6803 strains that differ in membrane lipid unsaturation

• Published in: Photosynthesis research 1999-03, Vol.59 (2-3), p.125-136
• Main Authors: Papageorgiou, George C, Govindjee, Govindjee, Rajni, Mimuro, Mamuro, Stamatakis, Kostas, Alygizaki-zorba, Aikaterini, Murata, Norio
• Format: Article
• Language: English
• Subjects: Chlorophyll; Cyanobacteria; Membranes; Proteins; Synechocystis
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1023/A:1006170829186

Membranes of wild-type (WT) cells of the cyanobacterium Synechocystis sp. PCC 6803 are abundant in polyunsaturated fatty acids in membrane lipids and thus more fluid than membranes of desA^sup -^/desD^sup -^ mutant cells which contain no polyunsaturated fatty acids. Using intact cells we examined the effects of normal and chilling temperatures on membrane fluidity-dependent properties. We probed the thylakoid membranes by inducing light/dark acclimative changes in chlorophyll a (Chl a) fluorescence; and we probed the plasma membranes either by suppressing the Chl a fluorescence of light-acclimated cells under hyper-osmotic conditions, or by measuring the electric conductivity of cell suspensions. Thylakoid membranes of mutant cells undergo reversible thermotropic transition between 19 °C and 22 °C (midpoint at 20.5 °C). No analogous transition was detected in the thylakoid membranes of WT cells in the temperature range from 2 to 34 °C. Plasma me mbranes of both WT and mutant cells did not experience thermotropic transition in the temperature range from 2 °C to 34 °C as detected either fluorimetrically or by means of electric conductivity. Hyper-osmotic conditions caused fast transient fluorescence quenching in WT cells at 34 °C, but not at 14 °C, and not in mutant cells at either 34 °C or 14 °C. This transient quenching sensed probably the higher fluidity of the plasma membranes of WT cells. Hyper-osmotic media and dark acclimation had similar effects on the 77 K fluorescence of Synechocystis cells: they suppressed the ratio of photosystem II fluorescence to photosystem I fluorescence.[PUBLICATION ABSTRACT]