Photosynthesis Research

, Volume 94, Issue 1, pp 109–120

Dark inactivation of ferredoxin-NADP reductase and cyclic electron flow under far-red light in sunflower leaves

Authors

  • Eero Talts
    • Institute for Molecular and Cell BiologyTartu University
  • Vello Oja
    • Institute for Molecular and Cell BiologyTartu University
  • Heikko Rämma
    • Institute for Molecular and Cell BiologyTartu University
  • Bahtijor Rasulov
    • Institute for Molecular and Cell BiologyTartu University
  • Agu Anijalg
    • Institute of PhysicsTartu University
    • Institute for Molecular and Cell BiologyTartu University
Research Article

DOI: 10.1007/s11120-007-9224-7

Cite this article as:
Talts, E., Oja, V., Rämma, H. et al. Photosynth Res (2007) 94: 109. doi:10.1007/s11120-007-9224-7

Abstract

The oxidation kinetics under far-red light (FRL) of photosystem I (PSI) high potential donors P700, plastocyanin (PC), and cytochrome f (Cyt f) were investigated in sunflower leaves with the help of a new high-sensitivity photometer at 810 nm. The slopes of the 810 nm signal were measured immediately before and after FRL was turned on or off. The same derivatives (slopes) were calculated from a mathematical model based on redox equilibrium between P700, PC and Cyt f and the parameters of the model were varied to fit the model to the measurements. Typical best-fit pool sizes were 1.0–1.5 μmol m−2 of P700, 3 PC/P700 and 1 Cyt f/P700, apparent equilibrium constants were 15 between P700 and PC and 3 between PC and Cyt f. Cyclic electron flow (CET) was calculated from the slope of the signal after FRL was turned off. CET activated as soon as electrons accumulated on the PSI acceptor side. The quantum yield of CET was close to unity. Consequently, all PSI in the leaf were able to perform in cycle, questioning the model of compartmentation of photosynthetic functions between the stroma and grana thylakoids. The induction of CET was very fast, showing that it was directly redox-controlled. After longer dark exposures CET dominated, because linear e transport was temporarily hindered by the dark inactivation of ferredoxin-NADP reductase.

Keywords

LeafPhotosystem ICyclic electron flowFar-red lightFerredoxin-NADP reductase

Abbreviations

CET

Cyclic electron transport

Cyt

Cytochrome

Fd

Ferredoxin

FNR

Ferredoxin-NADP reductase

FRL

Far-red light

PC

Plastocyanin

PFD, PAD

Photon flux density, incident and absorbed

PQ

Plastoquinone

PSI, PSII

Photosystem I and photosystem II

P700

Donor pigment of PSI

WL

White light

Copyright information

© Springer Science+Business Media B.V. 2007