PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

A study of unusual light-induced fluorescence changes in the SPCM mutant of Synechocystis PCC 6803. Matt Scott^*,1, Sergej Vasil'ev¹, Chantal McCollum¹, Cheryl Crozier², George Espie², Doug Bruce¹, ¹ Dept. of Biological Sciences, Brock University., St. Catharines, Ontario, Canada² Dept. of Botany, University of Toronto at Missisauga., Missisauga, Ontario, Canada

ABSTRACT- The SPCM mutant of Synechocystis PCC. 6803 is completely lacking both oxygen evolution activity and variable PSII fluorescence, however when exposed to actinic light it shows remarkably complex changes of the fluorescence intensity. When exposed to white light, the fluorescence intensity first increases (3 to 5 s) and then is quenched to a value of about 30% of the initial level (10 to 15 min). These changes are completely reversible, and the magnitude and kinetics are excitation wavelength dependent. We have studied the fluorescence properties of the SPCM mutant by steady-state, low temperature, pulse-amplitude modulated, and time-resolved fluorescence techniques. We have found a blue light action spectrum (peaking at 460 nm) for the light-induced quenching. Pronounced differences in picosecond fluorescence decay kinetics were also oversved between quenched and dark-adapted states. The maximum quenching in fluorescence decay kinetics was observed around 680 nm indicating that the quencher is associated with chlorophyll pigment-protein complexes and/or the phycobilisome terminal emitter. We propose that the observed blue light induced quenching in the mutant reflects a novel regulatory mechanism in cyanobacteria which is normally hidden behind the large variable Chl a fluorescence arising from active PSII reaction centers.

KEY WORDS: Quenching