Impair Of Photosystem II (PSII) Function During Day And Night
Cycles In Cyanobacterium Cyanothece sp. ATCC 51142 Is A Two
Phase Process Partly Dependent To Protein Synthesis
Iuliana Chis1, Oana Sicora1, Ciprian Chis1, Mara Ana Naghi1, Carmel Dalton1,2, Cosmin Sicora1
1
Biological Research Center Jibou, Romania
2 Western University “Vasile Goldis”, Arad, Romania
Email:[email protected]
Summary: Cyanobacteria have highly conserved photosynthetic machinery. The D1 protein, the core protein of Photosystem II, is an indispensable
component of oxygenic photosynthesis. The D1 protein is encoded by a psbA gene family, whose members are differentially expressed in different
environmental conditions. The D1 protein is expressed by 5 psbA genes, encoding 4 isoforms of the protein. Recent publications postulate the presence of
another class of cyanobacterial D1 proteins, D1 rogue class, which blocks the PSII during the night and allows the N2 fixation.
Cyanothece sp. ATCC 51142 is a unicellular, aerobic, diazotrophic cyanobacterium which fixes N2 in the dark. We measured the PSII function at cells grown in
continuous light and in 12 hours light-dark cycles. We observed changes in PSII function during night, a deceleration of the electron transfer between QA and QB
in the acceptor side of the electron transport chain and also a possible effect of the water oxidation complex in the donor side of the electron transport chain.
We used a protein synthesis inhibitor to discriminate between the temporary impairment of PSII and more profound changes caused by the exchange of the D1
proteins. Our results show that the inhibitory process recorded during night time is a combination of the two processes with a fast initial inhibition that is not
protein dependent and a later phase that requires synthesis of new proteins.
Materials and methods: Cyanothece sp. ATCC 51142 was obtained from the Biological Research Institute from Cluj Napoca, Romania. The strain was
grown at 30ºC and 50μmol photons m-2s-1 light, until a chlorophyll concentration of 6 μg chl ml-1. In order to investigate the changes in PS II function during 12 h
light/12 h dark cycles, we designed the following experiments: we performed flash fluorescence measurements on Cyanothece sp. ATCC 51142, every 60
minutes during 26 h, both in the absence and presence of DCMU (3-(3,4-Dichlorophenyl)-1,1-dimethylurea). We also measured chlorophyll fluorescence in the
presence of Lincomycin (300µg/ml), an inhibitor that blocks the synthesis of new proteins. As control, similar measurements were also performed on
Synechocystis sp. PCC 6803. The fluorescence measurements were made with an FL3500 fluorometer from Photon Systems Instruments, we used a QA
recombination protocol, then the results were processed in the Origin.v8.0 program and for each sample a Joliot Correction was applied before plotting the
graphs.
Figure 2: Changes in the number of PS II active centers
during a 12h Light/12h Dark cycle in Cyanothece sp. ATCC
51142 in absence (a) and presence (b) of DCMU
Figure 1: Changes of acceptor and donor side of PS II function
during light in Cyanothece sp. ATCC 51142
Figure 4: Changes of acceptor side of PS II function during
Light/Dark cycle in Cyanothece sp. ATCC 51142
Figure 6: T2 parameter evolution on the acceptor side of PS II
function during a 12h Light/12h Dark cycle in Cyanothece sp. ATCC
51142, in absence and presence of Lincomycin .
Figure 3: Changes of acceptor and donor side of PS II function during
dark in Cyanothece sp. ATCC 51142
Figure 5: Changes of donor side of PS II function during
Light/ Dark cycle in Cyanothece sp. ATCC 51142
Figure 7: Changes in the number of PS II active centers during a 12h
Light/12h Dark cycle in Cyanothece sp. ATCC 51142 in absence (a)
and presence (b) of DCMU
Figure 8: Changes of acceptor side of PS II function during dark in
Cyanothece sp. ATCC 51142, in absence and presence of Lincomycin.
Conclusions: We observed changes in PSII function during night, a deceleration of the electron transfer between QA and QB in the acceptor side of PSII
and also a possible effect of the water oxidation complex in the donor side. The effect is partly dependent on protein synthesis.
Our results show that the inhibitory process recorded during night time is a combination of the two processes with a fast initial inhibition that
is not protein dependent and a later phase that requires synthesis of new proteins.
Acknowledgement: This work was supported by a grant of the Romanian National Authority for Scientific Research, CNCS-UEFISCDI, project number
PN-II-ID-PCE-2011-3-0765.