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JXB Advance Access originally published online on April 12, 2007
Journal of Experimental Botany 2007 58(7):1603-1615; doi:10.1093/jxb/erl295
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Calystegines in potatoes with genetically engineered carbohydrate metabolism

Ute Richter1, Uwe Sonnewald2 and Birgit Dräger1,*

1Department of Pharmacy, Faculty of Science I Biosciences, Martin Luther University Halle-Wittenberg, Hoher Weg 8, D-06120 Halle, Germany
2Department of Biochemistry, Faculty of Science II, Friedrich-Alexander-University Erlangen-Nuremberg, Staudtstr. 5, D-91058 Erlangen, Germany

* To whom correspondence should be addressed. E-mail: birgit.draeger{at}pharmazie.uni-halle.de

Calystegines are hydroxylated nortropane alkaloids derived from the tropane alkaloid biosynthetic pathway. They are strong glycosidase inhibitors and occur in vegetables such as potatoes, tomatoes, and cabbage. Calystegine accumulation in root cultures was described to increase with carbohydrate availability. Whether this is indicative for the in planta situation is as yet unknown. Potatoes are model plants for the study of carbohydrate metabolism. Numerous transgenic potato lines with altered carbohydrate metabolism are available, but rarely were examined for alterations in secondary metabolism. In this study, calystegine accumulation and expression of biosynthetic enzymes were related to genetic modifications in carbohydrate metabolism in potato tubers. Tubers contained more soluble sugars due to overexpression of yeast invertase in the apoplast or in the cytosol, or due to antisense suppression of sucrose synthase. It is shown that the major part of calystegines in tubers originated from biosynthesis in plant roots. Yet, tuber calystegine levels responded to genetic alterations of carbohydrate metabolism in tubers. The strongest increase in calystegines was found in tubers with suppressed sucrose synthase activity. Transcripts and enzyme activities involved in calystegine biosynthesis largely concurred with product accumulation. Whole plant organs were examined similarly and displayed higher calystegines and corresponding enzyme activities in roots and stolons of plants with enhanced soluble sugars. Increases in calystegines appear to be linked to sucrose availability.

Key words: Antisense, calystegine, carbohydrate metabolism, invertase, overexpression, potato, sucrose synthase, tropane alkaloid biosynthesis

Received 14 August 2006; Revised 29 November 2006 Accepted 4 December 2006


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