Russian Journal of Plant Physiology

, Volume 52, Issue 3, pp 283–287 | Cite as

Identification of Ferredoxin-Dependent Cyclic Electron Transport around Photosystem I Using the Kinetics of Dark P700+ Reduction

  • N. G. Bukhov
  • E. A. Egorova


Kinetic curves of absorbance changes induced by far-red light (FR, 830 nm) (ΔA830), which reflect redox transformations of PSI primary electron donor, P700, were examined in intact barley (Hordeum vulgare L.) leaves. In intact leaves, FR induced the biphasic increase in absorbance related to P700 photooxidation. Leaf treatment with methyl viologen or antimycin A suppressed the slow phase of P700 photooxidation, which was attained in such leaves within the first second of light exposure. With FR turned off, the previously increased absorbance at 830 nm dropped down to its initial level, thus reflecting P700+ reduction. In the control leaves, the kinetics of P700+ reduction consisted of three exponentially decaying components, with the corresponding half-times of 8.8 s (the slow component, with its magnitude comprising 24% of the total ΔA830 signal), 0.73 s (the middle component, 49% of ΔA830), and 0.092 s (the fast component, 26% of ΔA830). The rate of the fast component of P700+ reduction, following FR irradiation of leaves, was about ten times lower than that of the noncyclic electron transfer from PSII to PSI computed from ΔA830 relaxation after the abrupt offset of white light. The treatment of leaves with methyl viologen or antimycin A completely abolished the fast component of ΔA830 relaxation after FR exposure. It was concluded that the fast component is determined by the operation of ferredoxin-dependent cyclic electron transport around PSI. This study represents the first report on the identification of this pathway of electron transport in vivo and the estimation of its rate.

Key words

Hordeum vulgare ferredoxin-dependent electron transport noncyclic electron transport stromal reductants photosystem I 







white light


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Copyright information

© MAIK “Nauka/Interperiodica” 2005

Authors and Affiliations

  • N. G. Bukhov
    • 1
  • E. A. Egorova
    • 1
  1. 1.Timiryazev Institute of Plant PhysiologyRussian Academy of SciencesMoscowRussia

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