Elucidating the toxicity targets of β-ionone on photosynthetic system of Microcystis aeruginosa NIES-843 (Cyanobacteria)

In order to explore the potential targets of toxicity of beta-ionone on the photosynthetic system of Microcystis aeruginosa, the polyphasic rise in chlorophyll a (Chl a) fluorescence transient and transcript expression for key genes in photosystem II (PSII) of M. aeruginosa NIES-843 were studied. The EC(50) value of beta-ionone on M. aeruginosa NIES-843 was found to be 21.23 +/- 1.87 mg/L It was shown that beta-Ionone stress can lead to a decrease in pigment content of M. aeruginosa NIES-843 cells, and that carotenoids were more sensitive to beta-ionone stress than Chl a. The normalized Chl a fluorescence transients were slightly decreased at 6.67 and 10 mg/L beta-ionone, but significantly increased at 15, 22.5 and 33.75 mg/L There was no significant variation on transcript expression of psbA and psbO at a concentration of 6.67 mg/L beta-ionone. but they were down-regulated at 22.5 mg/L Ultrastructural examination by transmission electron microscopy indicated that the thylakoids were distorted, and the thylakoid membrane stacks began to collapse when M. aeruginosa NIES-843 was exposed to beta-ionone at a concentration of 22.5 and 33.75 mg/L Our results indicate that the reaction centre of PS II and the electron transport at the acceptor side of PS II are the targets responsible for the toxicity of beta-ionone on the PS II of M. aeruginosa NIES-843. (C) 2011 Elsevier B.V. All rights reserved.