Prolonged incubation with low concentrations of mercury alters energy transfer and chlorophyll (Chl) a protein complexes in Synechococcus 6301: changes in Chl a absorption and emission characteristics and loss of the F695 emission band |
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Authors: | S. D. S. Murthy N. Mohanty Prasanna Mohanty |
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Affiliation: | (1) Bioenergetics and Photobiochemistry Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India;(2) School of Life Sciences, Jawaharlal Nehru University, 110 067 New Delhi, India |
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Abstract: | Synechococcus PCC 6301 cells grown in the presence of low sublethal levels of (about 2 m) mercury induced alterations in chlorophyll (Chl) a absorption without significant alterations in phycocyanin. Chl a fluorescence emission in Hg2+ -raised cells showed a large (about 18 nm) blue shift in the peak emission. No major spectral changes in phycobilisome (PBsome) emission characteristic were noticed, indicating major structural alterations in Chl-protein complexes by incubation with Hg2+ ions. Low temperature (77 K) emission spectra of cells grown in the presence of Hg2+ showed a loss of the characteristic Chl a emission band at 695 nm (F695), which is known to be linked to photosystem II photochemistry and to originate from the Chl a of core antenna polypeptide CP 47 of photosystem II. The SDS-PAGE polypeptide profile of thylakoids indicates a loss of a polypeptide(s) with a molecular mass between 40 and 60 k Da by Hg2+ incubation of cells. Our results suggest that prolonged incubation of Synechococcus 6301 cells with low concentrations of Hg2+ affects the Chl a spectral properties and the structure of Chl-protein complexes. |
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Keywords: | chlorophyll a energy transfer fluorescence mercury ions photosystem phycobilisomes Synechococcus 6301 |
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