Determination of the movement and persistence of Cry1Ab/1Ac protein released from Bt transgenic rice under field and hydroponic conditions

Bt rice may become the first commercially released staple food crop transformed with insecticidal genes derived from Bacillus thuringiensis (Bt). However, little information is available concerning the insecticidal protein released from Bt rice into the environment. A 3-year study was conducted to determine the amount, persistence and movement of Cry1Ab/1Ac protein released from Bt-Minghui63 (Bt-MH63) and Bt-Shanyou63 rice (Bt-SY63) using an enzyme-linked immunosorbent assay. The Cry1Ab/1Ac protein was detected in the water of Bt rice fields during the growth stage (below 0.03 ng ml−1 water), but it was not detected in the water of non-Bt fields. A basal level of Cry1Ab/1Ac protein was found in the rhizosphere soil of non-Bt rice (about 0.75 ng g−1 dried soil), and the amount of Cry1Ab/1Ac protein in the rhizosphere soil of Bt rice (about 1.49 ng g−1 dried soil) was significantly higher than that at the basal level. The amount of Cry1Ab/1Ac protein in soil did not significantly differ between non-Bt fields irrigated using water from Bt fields or from a reservoir. In the surface and 10 cm deep soil, the amount of Cry1Ab/1Ac protein differed significantly between Bt and non-Bt rice fields during the harvest period. The amount of Cry1Ab/1Ac protein in the rhizosphere soil of Bt rice was only significantly higher than the basal level during the first two months after harvest. Under hydroponic conditions, Bt rice released detectable Cry1Ab/1Ac protein to the nutrient solution, but artificial wounding in roots did not enhance the releasing of this protein. Based on the above results, we conclude that Bt-MH63 and Bt-SY63 rice can release detectable amounts of Cry1Ab/1Ac protein into soil and field water in the growth period but that the Bt protein does not move into adjacent paddies along with the irrigating water and does not persist in the soil for more than two months.