Journal Article

Tobacco plants that lack expression of functional nitrate reductase in roots show changes in growth rates and metabolite accumulation

Robert Hänsch, Desirée Gómez Fessel, Christina Witt, Christine Hesberg, Guido Hoffmann, Pia Walch‐Liu, Christof Engels, Jörg Kruse, Heinz Rennenberg, Werner M. Kaiser and Ralf‐R. Mendel

in Journal of Experimental Botany

Volume 52, issue 359, pages 1251-1258
Published in print June 2001 | ISSN: 0022-0957
Published online June 2001 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jexbot/52.359.1251
Tobacco plants that lack expression of functional nitrate reductase in roots show changes in growth rates and metabolite accumulation

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When tobacco is provided with a high nitrate supply, only a small amount of the nitrate taken up by the roots is immediately assimilated inside the roots, while the majority is transported to the leaves where it is reduced to ammonium. To elucidate the importance of root nitrate assimilation, tobacco plants have been engineered that showed no detectable nitrate reductase activity in the roots. These plants expressed the nitrate reductase structural gene nia2 under control of the leaf‐specific potato promoter ST‐LS1 in the nitrate reductase‐mutant Nia30 of Nicotiana tabacum. Homozygous T2‐transformants grown in sand or hydroponics with 5.1 mM nitrate had approximately 55–70% of wild‐type nitrate reductase acivity in leaves, but lacked nitrate reductase acivity in roots. These plants showed a retarded growth as compared with wild‐type plants. The activation state of nitrate reductase was unchanged; however, diurnal variation of nitrate reductase acivity was not as pronounced as in wild‐type plants. The transformants had higher levels of nitrate in the leaves and reduced amounts of glutamine both in leaves and roots, while roots showed higher levels of hexoses (3‐fold) and sucrose (10‐fold). It may be concluded that the loss of nitrate reductase acivity in the roots changes the allocation of reduced nitrogen compounds and sugars in the plant. These plants will be a useful tool for laboratories studying nitrate assimilation and its interactions with carbon metabolism.

Keywords: Diurnal variation; leaf specific expression; nitrate reductase; tobacco; roots.

Journal Article.  5973 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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