Genetically modified cotton producing a Bacillus thuringiensis (Bt) Cry1Ac toxin effective against insects is widely used in North America. In the elevated carbon dioxide levels expected in this century, toxin expression will be reduced: plants are unable to acquire enough nitrogen to meet both growth needs and the requirements for toxin production. Elevated atmospheric CO2 concentrations cause plants to grow faster, lower nitrogen content per unit of plant tissue, and generate higher carbon to nitrogen (C/N) ratios. We determined that production of transgenic proteins will be reduced, thus reducing the efficiency of Bacillus thuringiensis (Bt) transgenes against insect populations. This led us to test the hypotheses that transgenic cotton grown with excess nitrogen would increase toxin expression, but not uniformly across plant structures. In both experimental and commercial plantings, toxin production was not consistent between plant structures or over time. Our data, generated with a commercial ELISA technique, were substantially different from the previously reported Bt concentrations in that we found that the highest leaves on the plants, which generally act as sinks for N-based assimilates, had increased toxin concentrations over the season. Like previous studies, lower leaves were found to have reduced concentrations as plants aged. Enhanced insect protection with excessive nitrogen application suggests growers may be inclined to over apply nitrogen, risking nitrification of waterways and increasing costs.
Species 1: Lepidoptera Noctuidae Spodoptera exigua (beet armyworm)
Species 2: Malvales Malvaceae Gossypium hirsutum (cotton)
Keywords: Transgenic Bt
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