Phycobilin/chlorophyll excitation equilibration upon carotenoid-induced non-photochemical fluorescence quenching in phycobilisomes of the cyanobacterium Synechocystis sp. PCC 6803

Abstract

To determine the mechanism of carotenoid-sensitized non-photochemical quenching in cyanobacteria, the kinetics of blue-light-induced quenching and fluorescence spectra were studied in the wild type and mutants of Synechocystis sp. PCC 6803 grown with or without iron. The blue-light-induced quenching was observed in the wild type as well as in mutants lacking PS II or IsiA confirming that neither IsiA nor PS II is required for carotenoid-triggered fluorescence quenching. Both fluorescence at 660 nm (originating from phycobilisomes) and at 681 nm (which, upon 440 nm excitation originates mostly from chlorophyll) was quenched. However, no blue-light-induced changes in the fluorescence yield were observed in the apcE(-) mutant that lacks phycobilisome attachment. The results are interpreted to indicate that interaction of the Slr1963-associated carotenoid with--presumably--allophycocyanin in the phycobilisome core is responsible for non-photochemical energy quenching, and that excitations on chlorophyll in the thylakoid equilibrate sufficiently with excitations on allophycocyanin in wild type to contribute to quenching of chlorophyll fluorescence.

An Atypical psbA Gene Encodes a Sentinel D1 Protein to Form a Physiologically Relevant Inactive Photosystem II Complex in Cyanobacteria

“…Samples were excited at 435 nm, and emission spectra were adjusted for same signal at the fluorescein peak at 522 nm. The fluorescein component from emission spectra was subtracted and normalized to the 721 nm emission band (41).…”

A photoactive carotenoid protein acting as light intensity sensor

“…In contrast, the mechanism of thermal energy dissipation in cyanobacteria, which plays a key role in global carbon cycling, remained elusive. Only within the last few years has a photoprotective mechanism associated with the soluble phycobilisome antenna of PSII in cyanobacteria been demonstrated (8)(9)(10)(11)(12)(13)(14). A specific soluble carotenoid protein, the orange carotenoid protein (OCP), plays an essential role in this process (9,10).…”

The role of the orange carotenoid protein and PsbU protein in photoprotection in cyanobacteria

“…In previous studies it has been proposed that IsiA is involved in the generation of the large blue light-induced NPQ observed in Synechocystis under iron starvation (Cadoret et al, 2004). But later, it was shown that this iron-stress induced NPQ was OCP-but not IsiA-dependent (Rakhimberdieva et al, 2007;Wilson et al, 2007).…”

“…The function of the OCP in the photoprotective PB-related thermal dissipating mechanism has been examined so far only in Synechocystis cells (Wilson et al, 2006;Rakhimberdieva et al, 2007;Wilson et al, 2007). It is, however, not known if this important mechanism is widespread among cyanobacteria, or not.…”

“…For instance, in many cyanobacteria it induces the synthesis of the chlorophyll-binding protein IsiA (iron-stressinduced protein) (Laudenbach and Straus, 1988;Burnap et al, 1993). Under iron starvation conditions (Cadoret et al, 2004;Rakhimberdieva et al, 2007;Wilson et al, 2007) blue-green light induces a very large fluorescence quenching, which is much larger than under complete medium conditions. It was suggested that IsiA protein induce this NPQ.…”