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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Repression of a Novel Isoform of Disproportionating Enzyme (stDPE2) in Potato Leads to Inhibition of Starch Degradation in Leaves But Not Tubers Stored at Low Temperature¹

Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Golm, Germany (J.R.L.); Plant Research Department, Risø National Laboratory, DK–4000 Roskilde, Denmark (J.R.L., K.B., J.K.); and Plant Biochemistry Laboratory, Department of Plant Biology, Center for Molecular Plant Physiology, The Royal Veterinary and Agricultural University, DK–1871 Frederiksberg C, Copenhagen, Denmark (A.B.)

A potato (Solanum tuberosum) cDNA encoding an isoform of disproportionating enzyme (stDPE2) was identified in a functional screen in Escherichia coli. The stDPE2 protein was demonstrated to be present in chloroplasts and to accumulate at times of active starch degradation in potato leaves and tubers. Transgenic potato plants were made in which its presence was almost completely eliminated. It could be demonstrated that starch degradation was repressed in leaves of the transgenic plants but that cold-induced sweetening was not affected in tubers stored at 4°C. No evidence could be found for an effect of repression of stDPE2 on starch synthesis. The malto-oligosaccharide content of leaves from the transgenic plants was assessed. It was found that the amounts of malto-oligosaccharides increased in all plants during the dark period and that the transgenic lines accumulated up to 10-fold more than the control. Separation of these malto-oligosaccharides by high-performance anion-exchange chromatography with pulsed-amperometric detection showed that the only one that accumulated in the transgenic plants in comparison with the control was maltose. stDPE2 was purified to apparent homogeneity from potato tuber extracts and could be demonstrated to transfer glucose from maltose to oyster glycogen.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.038026.

^* Corresponding author; e-mail james.richard.lloyd{at}risoe.dk; fax 45–4677–4109.

Received December 22, 2003; returned for revision January 20, 2004; accepted January 26, 2004.

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