Quantification of cyclic electron flow around Photosystem I in spinach leaves during photosynthetic induction
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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.
KeywordsCyclic electron transport P700 Photosynthetic induction Photosystem I
- Fv′ and Fm′
Variable and maximum Chl fluorescence during illumination
Oxidized nicotinamide adenine dinucleotide phosphate
Photoactive Chl of the reaction centre of PS I
- PS I and PS II
Photosystem I and II, respectively
DF is supported in part by the National Natural Science Foundation of China (No. 90302004) and Knowledge Innovation Program of the Chinese Academy of Sciences (KSCX2-SW-109). Partial financial support of this project from an ARC grant DP 0665363 to BJP and WSC is gratefully acknowledged. ABH is grateful for a Visiting Fellowship from RSBS, ANU. We thank Jan Anderson and Tom Wydrzynski for constructive comments on the manuscript.
- Genty B, Briantais J-M, Baker NR (1989) The relationship between quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence. Biochim Biophys Acta 990:87–92Google Scholar
- Mi H, Endo T, Ogawa T, Asada K (1995) Thylakoid membrane-bound pyridine nucleotide dehydrogenase complex mediates cyclic electron transport in the cyanobacteria Synechocystis PCC 6803. Plant Cell Physiol 36:661–668Google Scholar
- Schreiber U (2004) Pulse-amplitude-modulation (PAM) fluorometry and saturation pulse method: an overview. In: Papageorgiou GC, Govindjee (eds) Advances in photosynthesis and respiration, vol 19, Chlorophyll a fluorescence: a signature of photosynthesis. Springer, Dordrecht, The Netherlands, pp 279–319Google Scholar
- Schreiber U, Hormann H, Asada K, Neubauer C (1995) O2-dependent electron flow in spinach chloroplasts: properties and possible regulation of the Mehler-ascorbate-peroxidase cycle. In: Mathis P (ed) Photosynthesis: from light to biosphere, vol II. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp 813–818Google Scholar