Interactions of elevated CO2 and nitrogen fertilization: Effects on production of Bacillus thuringiensis toxins in transgenic plants

Elevated atmospheric CO2 concentrations will cause plants to grow faster, l ower nitrogen content per unit of plant tissue, and generate higher carbon to nitrogen (C/N) ratios. We hypothesize that production of transgenic prot eins will be reduced, thus reducing the efficiency of Bacillus thuringiensi s (Bt) transgenes against insect populations. Commercially available transg enic cotton plants expressing the Cry 1Ac gene from Bt were compared with a near isogenic non-Bt cotton line in a split-plot design with two levels of atmospheric CO2 (ambient, 370 ppm and elevated, 900 ppm) incorporating a 2 X 2 factorial design with two nitrogen (N) fertilization regimes (low, 30 mg N/kg soil/wk and high, 130 mg N/kg soil/wk),and two levels of Bt (presen ce or absence). Bioassays using Spodoptera exigua (Hubner) and quantitative enzyme-linked immunosorbent assays for toxin content indicated reduced Bt protein production in elevated CO2. The tendency for test insects to consum e more foliage from plants with lower N, caused by the elevated CO2, did no t compensate for the reduction in toxin production. N fertilization regime interacted with CO2 concentration, showing that plants growing in N limited systems would produce-substantially less toxin. The use of transgenic plan ts is becoming increasingly important and will continue to be so in the nex t decades. At the same time, atmospheric CO2 increase will affect the effec tiveness of this strategy. These observations have implications not only fo r agricultural use of transgenic plants, but also for the ecological conseq uences of transfer of Bt toxins to closely related wild plant genotypes.