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 lambda(ex) = 655 nm were found to be 896, 220 and 83 angstrom(2) 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 phycobifisomes. The rate constant of energy migration was found to be equal to 1.04 x 10(10) s(-1). (C) 2011 Elsevier B.V. All rights reserved.