DECOMPOSITION OF GENETICALLY-ENGINEERED TOBACCO UNDER FIELD CONDITIONS - PERSISTENCE OF THE PROTEINASE-INHIBITOR-I PRODUCT AND EFFECTS ON SOIL MICROBIAL RESPIRATION AND PROTOZOA, NEMATODE AND MICROARTHROPOD POPULATIONS

1. To evaluate the potential effects of genetically engineered (transg enic) plants on soil ecosystems, litterbags containing leaves of non-e ngineered (parental) and transgenic tobacco plants were buried in fiel d plots. The transgenic tobacco plants were genetically engineered to constitutively produce proteinase inhibitor I, a protein with insectic idal activity. 2. The litterbag contents and surrounding soil, as well as soil from control plots without litterbags, were sampled over a 5- month period at 2- to 4-week intervals and assayed for proteinase inhi bitor concentration, litter decomposition rates, carbon and nitrogen c ontent, microbial respiration rates and population levels of nematodes , protozoa and microarthropods, 3. The proteinase inhibitor concentrat ion in the transgenic plant litter after 57 days was 0.05% of the samp le day 0-value and was not detectable on subsequent sample days, Altho ugh the carbon content of the transgenic plant litter was comparable t o that of the parental plant litter on sample day 0, it became signifi cantly lower over the course of the experiment. 4. Nematode population s in the soil surrounding the transgenic plant litterbags were greater than those in the soil surrounding parental plant litterbags and had a different trophic group composition, including a significantly highe r ratio of fungal feeding nr nematodes to bacterial feeding nematodes on sample day 57. In contrast, Collembola populations in the soil surr ounding the transgenic plant litterbags were significantly lower than in the soil surrounding parental plant litterbags. 5. Our results demo nstrated that under field conditions proteinase inhibitor remained imm unologically active in buried transgenic plant litter for at least 57 days and that decomposing parental and transgenic plant litter differe d in quality (carbon content) and in the response of exposed soil orga nisms (Collembola and nematodes).