Results regarding the levels of Cry1Ab protein in transgenic corn tissue (MON810) and the fate of Bt protein in three soil types

Abstract

Since the introduction of insect-resistant crops in 1996, cultivation of this group of genetically modified crops has grown substantially. There are many Bt corn events in field trials, but only one is commercialized on the Romanian market. The levels of the protein in plant tissue would be valuable in determining the protein concentration to which nontarget organisms may be exposed. The soil fate of the Bt protein is a key parameter governing exposure of nontarget organisms in this environment. The objectives of our study were: (i) to investigate the impact of the soil type on Bt expression levels in transgenic corn tissue (leaves, roots seed); (ii) to monitor the time-dependent degradation of the cry1Ab protein in three soil types favorable for corn growing, with different physicochemical characteristics. Detection and quantification of Cry1Ab protein in tissue (leaves, roots and seeds) and soil extracts was conducted using ELISA method with a commercially available test system for detecting Cry1Ab/Cry1Ac proteins (QuantiPlate Kit for Cry1Ab/Cry1Ac; Agdia), following the recommended protocol of the manufacturer. To evaluate the potential of Bacillus thuringiensis (Bt) Cry1Ab protein accumulation in soil, transgenic corn containing event MON 810 encoding the cry1Ab gene was grown in greenhouse conditions in pots containing three types of soil. At the end of growing period, the corn plants were incorporated into the soil. During vegetative period and at different time points after biomass incorporation, soil samples were collected from pots, and the level of Cry1Ab protein in these samples was determined using ELISA assay. Regarding Bt protein content, there is no difference between plants grown in different soils types. The lowest Bt protein content was quantified in senescent tissue and in seeds. The average chart for test soils shows an initial Bt protein increase after incorporating the plant biomass into the greenhouse soil pots, with the Cry1Ab concentration peaking at about 6 -9 weeks after incorporation, and declining slowly towards the 12-15 week (3-4 months) sampling interval. Overall, our results supports the conclusion that the Cry1Ab protein does not persist or accumulate in soil after incorporation in the soil of Bt corn plants expressing this protein.