Plant Physiol. Drug Metab Dispos
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Antisense Repression of Hexokinase 1 Leads to an Overaccumulation of Starch in Leaves of Transgenic Potato Plants But Not to Significant Changes in Tuber Carbohydrate Metabolism1

Jon Veramendi2, *, Ute Roessner, Andreas Renz, Lothar Willmitzer, and Richard N. Trethewey3

Max Planck Institut für Molekulare Pflanzenphysiologie, Karl Liebknecht Strasse 25, 14476 Golm, Germany

Potato (Solanum tuberosum L.) plants transformed with sense and antisense constructs of a cDNA encoding the potato hexokinase 1 (StHK1) exhibited altered enzyme activities and expression of StHK1 mRNA. Measurements of the maximum catalytic activity of hexokinase revealed a 22-fold variation in leaves (from 22% of the wild-type activity in antisense transformants to 485% activity in sense transformants) and a 7-fold variation in developing tubers (from 32% of the wild-type activity in antisense transformants to 222% activity in sense transformants). Despite the wide range of hexokinase activities, no change was found in the fresh weight yield, starch, sugar, or metabolite levels of transgenic tubers. However, there was a 3-fold increase in the starch content of leaves from the antisense transformants after the dark period. Starch accumulation at the end of the night period was correlated with a 2-fold increase of glucose and a decrease of sucrose content. These results provide strong support for the hypothesis that glucose is a primary product of transitory starch degradation and is the sugar that is exported to the cytosol at night to support sucrose biosynthesis.

1   This work was supported by a grant from the Alexander von Humboldt Foundation to J.V.
2   Present address: Departamento de Producción Agraria, Universidad Pública de Navarra. Campus Arrosadía, 31006 Pamplona, Spain.
3   Present address: Metanomics GmbH & Co. KGaA, Tegeler Weg 33, 10589 Berlin, Germany.
*   Corresponding author; e-mail jon{at}upna.es; fax 34-948-232191.

Plant Physiol. (1999) 121: 123-134
Copyright Clearance Center:   0032-0889/99/121//12
© 1999 American Society of Plant Physiologists




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