Photosystem 2 effective fluorescence cross-section of cyanobacterium Synechocystis sp. PCC6803 and its mutants

The effective fluorescence cross-section of photosystem 2 (PS2) was defined by measurements of chlorophyll a fluorescence induction curves for the wild type of the unicellular cyanobacterium Synechocystis sp. PCC6803, C-phycocyanin deficient mutant (CK), and mutant that totally lacks phycobilisomes (PAL). It was shown that mutations lead to a strong decrease of the PS2 effective fluorescence cross-section. For instance, the effective fluorescence cross-section of PS2 for wild type, CK and PAL mutants excited at λex = 655 nm were found to be 896, 220 and 83 Å2 respectively. Here we present an estimation of energy transfer efficiency from phycobilisomes to the pigment-protein complexes of PS2. It was shown that the PS2 fluorescence enhancement coefficient reaches a maximum value of 10.7 due to the energy migration from phycobilisomes. The rate constant of energy migration was found to be equal to 1.04 × 1010 s−1.

Research highlights
► Fluorescence induction curves of Synechocystis sp. PCC6803 and its mutants were studied.
► It was shown that mutations lead to a strong decrease of PS2 effective fluorescence cross-section.
► PS2 fluorescence enhancement coefficient reaches 10.7 due to energy migration from phycobilisomes.
► The rate constant of energy migration was found to be equal to 1.04 1010 s−1.