Ammonia triggers photodamage of photosystem II in the cyanobacterium Synechocystis sp. strain PCC 6803 |
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Authors: | Drath Miriam Kloft Nicole Batschauer Alfred Marin Kay Novak Jens Forchhammer Karl |
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Institution: | Institut für Mikrobiologie und Molekularbiologie, Justus-Liebig-Universit?t Giessen, D-35392 Giessen, Germany. |
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Abstract: | Ammonia has long been known to be toxic for many photosynthetic organisms; however, the target for its toxicity remains elusive. Here, we show that in the cyanobacterium Synechocystis sp. strain PCC 6803, ammonia triggers a rapid photodamage of photosystem II (PSII). Whereas wild-type cells can cope with this damage by turning on the FtsH2-dependent PSII repair cycle, the FtsH2-deficient mutant is highly sensitive and loses PSII activity at millimolar concentration of ammonia. Ammonia-triggered PSII destruction is light dependent and occurs already at low photon fluence rates. Experiments with monochromatic light showed that ammonia-promoted PSII photoinhibition is executed by wavebands known to directly destroy the manganese cluster in the PSII oxygen-evolving complex, suggesting that the oxygen-evolving complex may be a direct target for ammonia toxicity. |
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