Directed disruption of the tobacco ndhB gene impairs cyclic electron flow around photosystem I.
To evaluate the physiological significance of cyclic electron flow around photosystem (PS) I, we used a reverse genetic approach to focus on 11 chloroplast genes that encode homologs of mitochondrial complex I subunits (ndhA-K). Since their discovery, the exact function of the respiratory components in plant chloroplasts has been a matter of discussion. We disrupted one of these genes (ndhB) in tobacco by chloroplast transformation. Analysis of the transient increase in chlorophyll fluorescence after actinic light illumination and the redox kinetics of P700 (reaction center chlorophylls of PS I) suggest that the cyclic electron flow around PS I is impaired in the ndhB-deficient transformants. Transformants grew normally in a greenhouse, suggesting that the cyclic electron flow around PS I mediated by ndh gene products is dispensable in tobacco under mild environmental conditions.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0101 Japan.
T
T
Shikanai
T
T
Endo
T
T
Hashimoto
Y
Y
Yamada
K
K
Asada
A
A
Yokota
D000255:Adenosine Triphosphate / Q000378:metabolism; D001483:Base Sequence; D002734:Chlorophyll / Q000378:metabolism; D017931:DNA Primers; D004583:Electrons; D017343:Genes, Plant; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000235:genetics*; D010947:Plants, Toxic; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic
D017931:DNA Primers; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D000255:Adenosine Triphosphate