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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Decreased Expression of Cytosolic Pyruvate Kinase in Potato Tubers Leads to a Decline in Pyruvate Resulting in an in Vivo Repression of the Alternative Oxidase^1,[W],[OA]

Max-Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany (S.N.O., J.E.L., E.U.W., A.L., J.T.v.D., B.F., A.R.F., P.G.); Leibniz-Institute of Vegetable and Ornamental Crops, 14979 Grossbeeren, Germany (P.G.); and University of Potsdam, Institute of Chemistry and Interdisciplinary Center for Photonics, 14476 Potsdam-Golm, Germany (E.S.)

The aim of this work was to investigate the effect of decreased cytosolic pyruvate kinase (PKc) on potato (Solanum tuberosum) tuber metabolism. Transgenic potato plants with strongly reduced levels of PKc were generated by RNA interference gene silencing under the control of a tuber-specific promoter. Metabolite profiling showed that decreased PKc activity led to a decrease in the levels of pyruvate and some other organic acids involved in the tricarboxylic acid cycle. Flux analysis showed that this was accompanied by changes in carbon partitioning, with carbon flux being diverted from glycolysis toward starch synthesis. However, this metabolic shift was relatively small and hence did not result in enhanced starch levels in the tubers. Although total respiration rates and the ATP to ADP ratio were largely unchanged, transgenic tubers showed a strong decrease in the levels of alternative oxidase (AOX) protein and a corresponding decrease in the capacity of the alternative pathway of respiration. External feeding of pyruvate to tuber tissue or isolated mitochondria resulted in activation of the AOX pathway, both in the wild type and the PKc transgenic lines, providing direct evidence for the regulation of AOX by changes in pyruvate levels. Overall, these results provide evidence for a crucial role of PKc in the regulation of pyruvate levels as well as the level of the AOX in heterotrophic plant tissue, and furthermore reveal that these parameters are interlinked in vivo.

² Present address: CSIRO Plant Industry, Clunies Ross St., Canberra, ACT 2601, Australia.

³ Present address: Samuel Roberts Noble Foundation, 2510 Sam Noble Pkwy., Ardmore, OK 73401.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Peter Geigenberger (geigenberger{at}igzev.de).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.126516

^* Corresponding author; e-mail geigenberger{at}igzev.de.

Received July 16, 2008; accepted September 24, 2008; published October 1, 2008.

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