CHLOROPHYLL FLUORESCENCE QUENCHING CAUSED BY INORGANIC CARBON DEPLETION IN THE GREEN-ALGA SCENEDESMUS-QUADRICAUDA

The effect of inorganic (IC) depletion on fluorescence quenching was s tudied under laboratory conditions using the chlorococcal alga Scenede smus quadricauda strain Greifswald/15. The absence of IC caused a decr ease in photochemical quenching (q(p)), fluorescence yield (F-v/F-m) a nd the photosystem 2 photochemical yield (dF/F-m), and an increase of non-photochemical quenching (q(N)). High external pH (about 11), which accompanies the IC-depletion, did not have any remarkable effect on t he algae. Fluorescence parameters were reversed by a resupply of CO2. The IC-deficient algae when exposed to high irradiance appeared to be less sensitive to the photoinhibition than the algae supplied with CO2 . Increased thermal dissipation of the excitation energy (non-photoche mical quenching) in the absence of IC is one of the probable protectiv e mechanisms against photoinhibitory damage.