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Transgenic tobacco with resistance to bleaching herbicides had altered composition of carotenoids.

Manipulated Organism: Tobacco (Nicotiana tabacum cultivar Samsun and N. tabacum cultivar Xanthi nc).

Inserted Transgenes: crtl gene for producing phytoene desaturase, derived from the nonphotosynthetic bacterium, Erwinia urodovora. Promoter not indicated.

Goal: Produce transgenic tobacco and ultimately other crops that are resistant to bleaching herbicides.

Intended Effect: The transgenic plants showed strong resistance to various bleaching herbicides (for example, norflurazon, fluridone, flurtamone, fluorochloridone and diflufenican). Bleaching herbicides kill weeds and nontransgenic crops by interfering with (plant-type) phytoene desaturase and blocking the carotenoid pathway.

Unintended Effects: The composition of different carotenoids in the leaves of the transgenic tobacco was changed compared to unmanipulated controls. For example:
  • The levels of beta-carotene and derived xanthophylls, such as violaxanthin, were increased. The total amounts of these substances in transgenic leaves were about 55% of total carotenoids, in untransformed leaves only 38%.
  • The level of lutein, a xanthophyll derived from alpha-carotene, was reduced. In the transgenic tobacco leaves the level of lutein was 30% of total carotenoids, in the leaves of untransformed controls 50% of total carotenoids.

Additional Comments: These results suggest that making a food crop herbicide-resistant through an enzyme that alters carotenoid composition may have consequences for its nutritive value. Interestingly, in this experiment, despite the difference in composition of carotenoids, the total amounts of carotenoids in transgenic plants and control plants were similar.

Source: Misawa, N., K. Masamoto, T. Hori, T. Ohtani et al. (1994). "Expression of an Erwinia Phytoene Desaturase Gene not only Confers Multiple Resistance to Herbicides Interfering with Carotenoid Biosynthesis But Also Alters Xanthophyll Metabolism in Transgenic Plants," The Plant Journal, vol. 6, pp. 481-9.

Author Affiliations: Central Laboratories for Key Technology, Yokohama-shi, Japan; Department of Education, Kumamoto University, Japan; Universität Konstanz, Germany; J.W. Goethe Universität, Frankfurt, Germany.

Funding: EC Biotechnology Programme (partial).

Product Status: Not on the market as of 2008.

Copyright 2008 The Nature Institute.

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