title: Quantification of cyclic electron flow around Photosystem I in spinach leaves during photosynthetic induction.
abstract: The variation of the rate of cyclic electron transport around Photosystem I (PS I) during photosynthetic induction was investigated by illuminating dark-adapted spinach leaf discs with red + far-red actinic light for a varied duration, followed by abruptly turning off the light. The post-illumination re-reduction kinetics of P700+, the oxidized form of the photoactive chlorophyll of the reaction centre of PS I (normalized to the total P700 content), was well described by the sum of three negative exponential terms. The analysis gave a light-induced total electron flux from which the linear electron flux through PS II and PS I could be subtracted, yielding a cyclic electron flux. Our results show that the cyclic electron flux was small in the very early phase of photosynthetic induction, rose to a maximum at about 30 s of illumination, and declined subsequently to <10% of the total electron flux in the steady state. Further, this cyclic electron flow, largely responsible for the fast and intermediate exponential decays, was sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, suggesting an important role of redox poising of the cyclic components for optimal function. Significantly, our results demonstrate that analysis of the post-illumination re-reduction kinetics of P700+ allows the quantification of the cyclic electron flux in intact leaves by a relatively straightforward method.
authors.affiliation: Laboratory of Quantitative Vegetation Ecology, Institute of Botany, The Chinese Academy of Sciences, Beijing, 100093, China.
authors.forename: Da-Yong
authors.initials: DY
authors.lastname: Fan
authors.forename: Qin
authors.initials: Q
authors.lastname: Nie
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Hope
authors.forename: Warwick
authors.initials: W
authors.lastname: Hillier
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Pogson
authors.forename: Wah Soon
authors.initials: WS
authors.lastname: Chow
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D004579:Electron Transport / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology*; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D018724:Spinacia oleracea / Q000378:metabolism*
chemical_list: D045331:Photosystem I Protein Complex; D002734:Chlorophyll