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.
Target 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.
Nontarget 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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