The effect of inorganic (IC) depletion on fluorescence quenching was studied under laboratory conditions using the chlorococcal alga Scenedesmus quadricauda strain Greifswald/15. The absence of IC caused a decrease in photochemical quenching (^p), fluorescence yield and the photosystem 2 photochemical yield (dF/F^), and an increase of non-photochemical quenching {q^). High extemal pH (about 11), which accompanies the IC-depletion, did not háve any remarkable effect on the algae. Fluorescence parameters were reversed by a resupply of CO2. The IC-defícient 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-photochemical quenching) in the absence of IC is one of the probable protective mechanisms against photoinhibitory damage.
The bicarbonate compensation concentration (BCC) measmed in Scenedesmus quadricauda increased significantly with increasing total alkalínity (TA): ířom 2-5 inmol(HC03') m'^ at an alkalinity of 0.5 mol m'^ to 416-444 mmol(HC03") m"^ at an alkalinity of 10 mol m'^. This should be taken into account when evaluating a species ability to use HC03’. The increase of BCC at higher alkalinities could be caused by carbonate inhibition of HC03‘ uptake and/or by extremely high assimilatory pH reached.
A strain of Synechocystis sp. PCC 6803 expressing the yellow fluorescent protein (YFP) fused to the C-terminus of the PsaF subunit of PSI has been constructed and used to isolate native PSI complexes employing the GFP-Trap®, an efficient immunoprecipitation system which recognizes the green fluorescent protein (GFP) and its variants. The protein analysis and spectroscopic characterization of the preparation revealed an isolate of trimeric and monomeric PSI complexes, which showed minimal unspecific contamination as demonstrated by comparison with the wild type control. Interestingly, we detected CP43 subunits of PSII and small amounts of PSII core complexes specifically pulled-down with the YFP-PSI, supporting the association of PSII assembly modules and intermediate assembly complexes with PSI, as observed in our previous studies. The results demonstrate that the GFP-Trap® system represents an excellent tool for studies of PSI biogenesis and interconnection of PSI and PSII assembly processes., A. Strašková, J. Knoppová, J. Komenda., and Obsahuje bibliografické odkazy