Synechocystis sp. PCC 6803 mutant lacking both photosystems exhibits strong carotenoid-induced quenching of phycobilisome fluorescence

Blue light induced quenching in a Synechocystis sp. PCC 6803 strain lacking both photosystems is only related to allophycocyanin fluorescence. A fivefold decrease in the fluorescence level in two bands near 660 and 680 nm is attributed to different allophycocyanin forms in the phycobilisome core. Some low-heat sensitive component inactivated at 53 °C is involved in the quenching process. Enormous allophycocyanin fluorescence in the absence of the photosystems reveals a dark stage in this quenching. Thus, we present evidence that light activation of the carotenoid-binding protein and formation of a quenching center within the phycobilisome core in vivo are discrete events in a multistep process.