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Balancing the two photosystems: photosynthetic electron transfer governs

Summary: Balancing the two photosystems:
photosynthetic electron transfer governs
transcription of reaction centre genes
in chloroplasts
John F. Allen1*
and Thomas Pfannschmidt2
Department of Plant Biochemistry, Lund University, Box 117, SE-221 00 Lund, Sweden
2Friedrich-Schiller University of Jena, Institute of General Botany, Department of Plant Physiology, Dornburger Strasse 159,
D- 07743 Jena, Germany
Chloroplasts are cytoplasmic organelles whose primary function is photosynthesis, but which also contain
small, specialized and quasi-autonomous genetic systems. In photosynthesis, two energy converting
photosystems are connected, electrochemically, in series. The connecting electron carriers are oxidized by
photosystem I (PS I) and reduced by photosystem II (PS II). It has recently been shown that the
oxidation^reduction state of one connecting electron carrier, plastoquinone, controls transcription of
chloroplast genes for reaction centre proteins of the two photosystems. The control counteracts the im-
balance in electron transport that causes it: oxidized plastoquinone induces PS II and represses PS I;
reduced plastoquinone induces PS I and represses PS II. This complementarity is observed both in vivo,
using light favouring one or other photosystem, and in vitro, when site-speciąc electron transport inhibitors
are added to transcriptionally and photosynthetically active chloroplasts. There is thus a transcriptional


Source: Allen, John F. - School of Biological and Chemical Sciences, Queen Mary, University of London


Collections: Renewable Energy; Biology and Medicine