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J. Biol. Chem., Vol. 276, Issue 23, 20795-20802, June 8, 2001

This Article Full Text Full Text (PDF) All Versions of this Article: 276/23/20795    most recent M101255200v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Baena-González, E. Articles by Mäenpää, P. Search for Related Content PubMed PubMed Citation Articles by Baena-González, E. Articles by Mäenpää, P. Social Bookmarking                      What's this?

Abnormal Regulation of Photosynthetic Electron Transport in a Chloroplast ycf9 Inactivation Mutant^*

Elena Baena-González, John C. Gray^§, Esa Tyystjärvi, Eva-Mari Aro^¶, and Pirkko Mäenpää

From the  Department of Biology, Plant Physiology and Molecular Biology, University of Turku, FIN-20014 Turku, Finland and the ^§ Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, United Kingdom

The ycf9 (orf62) gene of the plastid genome encodes a 6.6-kDa protein (ORF62) of thylakoid membranes. To elucidate the role of the ORF62 protein, the coding region of the gene was disrupted with an aadA cassette, yielding mutant plants that were nearly (more than 95%) homoplasmic for ycf9 inactivation. The ycf9 mutant had no altered phenotype under standard growth conditions, but its growth rate was severely reduced under suboptimal irradiances. On the other hand, it was less susceptible to photodamage than the wild type. ycf9 inactivation resulted in a clear reduction in protein amounts of CP26, the NAD(P)H dehydrogenase complex, and the plastid terminal oxidase. Furthermore, depletion of ORF62 led to a faster flow of electrons to photosystem I without a change in the maximum electron transfer capacity of photosystem II. Despite the reduction of CP26 in the mutant thylakoids, no differences in PSII oxygen evolution rates were evident even at low light intensities. On the other hand, the ycf9 mutant presented deficiencies in the capacity for PSII-independent electron transport (ferredoxin-dependent cyclic electron transport and NAD(P)H dehydrogenase-mediated plastoquinone reduction). Altogether, it is shown that depletion of ORF62 leads to anomalies in the photosynthetic electron transfer chain and in the regulation of electron partitioning among the different routes of electron transport.

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