Rezumat articol ediţie STUDIA UNIVERSITATIS BABEŞ-BOLYAI

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The cyanobacterium Synechocystis sp. PCC 6803 grown on BG 11 medium under air bubbling was exposed to high light intensities of 2000, 3000 and 4500 µmol.m-2.s-1 while being in the exponential growth phase. The effect of light treatment was assessed after 15, 30, 45, 60, 75, 90, 105 and 120 minutes by monitoring chlorophyll fluorescence. F₀, F_m, Fv/Fm and Y(II) have significantly decreased under high light. The enhancement of the quantum yield of non-regular energy dissipation Y(NO) indicates that both the conversion of photochemical energy and the protective regulating mechanisms are inefficient. The increase of Y(NO) certifies the intensification of dissipation processes which take place mainly in the light harvesting antenna, in phycobilisomes. The high light intensities have led to the photoinhibition of the photosystem (PS) II antenna, affecting the reaction centers because Fv/Fm was decreased. The recovery of PSII photochemical activity was in overall a slow process correlated with light intensity that was used.

Keywords: chlorophyll fluorescence; coefficient of photochemical quenching (qP, qL); effective PS II quantum yield (YII); fluorescence yield; minimal fluorescence; maximal fluorescence; maximal PS II quantum yield (Fv/Fm); quantum yield of non-regulated energy dissipation (YNO); recovery.