Plant and Cell Physiology Advance Access originally published online on October 15, 2007
Plant and Cell Physiology 2007 48(11):1575-1588; doi:10.1093/pcp/pcm129
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Rates and Roles of Cyclic and Alternative Electron Flow in Potato Leaves
1Tartu Ülikooli Molekulaar- ja Rakubioloogia Instituut, Riia tn. 23, Tartu, 51010, Estonia
2Pflanzenphysiologie, FB5, Universität Osnabrück, D-49069 Osnabrück, Germany
*Corresponding author: E-mail, alaisk{at}ut.ee; Fax, +372-736-6021.
 |
Abstract |
|---|
Measurements of 810 nm transmittance changes in leaves, simultaneously with Chl fluorescence, CO2 uptake and O2 evolution, were carried out on potato (Solanum tuberosum L.) leaves with altered expression of plastidic NADP-dependent malate dehydrogenase. Electron transport rates were calculated: JC from the CO2 uptake rate considering ribulose-1,5-bisphosphate (RuBP) carboxylation and oxygenation, JO from the O2 evolution rate, JF from Chl fluorescence parameters and JI from the post-illumination re-reduction speed of PSI donors. In the absence of external O2, JO equaled (1.005 ± 0.003) JC, independent of the transgenic treatment, light intensity and CO2 concentration. This showed that nitrite and oxaloacetate reduction rates were very slow. The Mehler-type O2 reduction was evaluated from the rate of electron accumulation at PSI after the O2 concentration was decreased from 210 to 20 mmol mol–1, and resulted in <1% of the linear flow. JF and JI did not differ from JC while photosynthesis was light-limited, but considerably exceeded JC at saturating light. Then, typically, JF = 1.2 JC and JI = 1.3 JC, and JF –JC and JI –JC depended little on CO2 and O2 concentrations. The results showed that the alternative and cyclic electron flow necessary to compensate variations in the ATP/NADPH ratio were only a few percent of the linear flow. The data do not support the requirement of 14H+/3ATP by the chloroplast ATP synthase. We suggest that the fast PSI cyclic electron flow JI – JC, as well as the fast JF – JC are energy-dissipating cycles around PSI and PSII at light saturation.
Keywords: Alternative - Cyclic - Electron transport - Leaf
Abbreviations: Ac, Ao, CO2 and O2 gas exchange rates, respectively; aII, aI, excitation partitioning to PSII and PSI, respectively; BPGA, bisphosphoglycerate; Ci, Cw, Cc, CO2 concentration in intracellular space, dissolved in the cell wall liquid and at the Rubisco sites, respectively; CROC, carbon reduction–oxidation cycle; Cyt b6f, cytochrome b6f complex; Cyt f, cytochrome f; Fd, ferredoxin; Fm, F, Chl fluorescence yield under actinic light; FNR, flavoprotein ferredoxin–NADP reductase; electron flow rates, JAlt, to alternative acceptors, JC, for BPGA reduction, JCyc, cyclic around PSI, JF, through PSII, detected from fluorescence; JO, through PSII, detected from O2 evolution; JI, through PSI; MDH, NADPH-linked chloroplast malate dehydrogenase; OA, oxaloacetate; PFD, PAD, photon flux density, incident and absorbed, respectively; PC, plastocyanin; PEP, phosphoenol pyruvate; P700, donor pigment of PSI; RuBP, ribulose-1,5-bisphosphate
(Received July 13, 2007; Accepted October 3, 2007)
CiteULike 
Connotea 
Del.icio.us What's this?