Inactivation of chloroplast photosynthetic electron-transport activity by Ni |
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Authors: | B C Tripathy B Bhatia Prasanna Mohanty |
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Institution: | School of Life Sciences and School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India |
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Abstract: | Ni2+ inhibits electron-transport activity of isolated barley chloroplasts and this inhibition of electron transport by Ni2+ is distinctly different from other heavy metal ion (e.g., Pb2+, Cd2+, Zn2+)-induced inhibition of chloroplast function. Ni2+ inactivates Photosystem II (PS II) activity at a lower concentration than that required for the same extent of inhibition of Photosystem I (PS I)-mediated electron flow. Ni2+ induces changes in chlorophyll a (Chl a) emission characteristics and brings about a lowering of the Chl a fluorescence yield, and this lowering of Chl a fluorescence intensity is not relieved by the exogenously supplied electron donor NH2OH which donates electrons very close to the PS II reaction centres. Immobilization of the chloroplast membrane structure with glutaraldehyde fails to arrest the Ni2+-induced loss of PS II activity. Also, Ni2+-treated chloroplasts do not regain the ability to photoreduce 2,6-dichlorophenolindophenol even after washing of chloroplasts with buffer. These results indicate that unlike Zn2+ or Pb2+, Ni2+ induces alterations in the chloroplast photosynthetic apparatus resulting in an irreversible loss of electron-transport activity. |
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Keywords: | Chlorophyll a fluorescence Electron transport Ni2+ inhibition Photosynthesis (Barley chloroplast) |
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