Environmental Dynamics Of Cry1Ab Expressed By Transgenic Bt Rice And Effects On Non-Target Insects In Rice Paddy Habitat

Since the emergence of the first transgenic Bt plant in 1986, an increasing attention has been paid on the potential ecological risk brought about by the release of the transgenic Bt plants. Laboratory and field studies using two transgenic Bt rice, KMD1 and KMD2, containing a synthetic crylAb from Bacillus thuringiensis under the control of maize ubiquitin promoter, were carried out to investigate the degradation dynamics of CrylAb from Bt rice in environment and the relevant ecological risks to some non-target insects. The results are as follows:1. Degradation dynamics of CrylAb insecticidal protein from transgenic Bt rice in paddy soils and the relevant environment factorsThree types of paddy soils, i.e., blue clayey paddy soil, pale paddy soil on quaternary red soil and marine-fluvigenic yellow loamy paddy soil, were used. The degradation dynamics of CrylAb from ground dry powders of KMD2 leaf-blades in each type of soil, and the degradation dynamics of CrylAb from Huachi B6 leaf-blades and CrylAb from KMD1 stems and leaf-blades in flooded and unflooded soil of each type, were determined. Moreover, the effects of soil microbe, water content, pH value of soil and temperature on the degradation were also studied. It was found that, in each type of soils, the degradation rate of CrylAb was high during early experimental stage, but it slowed down steadily during middle and later stages, which could be described by exponential equations, with the half-life period of degradation determined as 1.8-11.6 d. Degradation rate of CrylAb protein from Bt rice tissue was closely related to the soil types, with the highest rate in blue clayey paddy soil, and the lowest in marine-fluvigenic yellow loamy paddy soil. Watering accelerated the degradation of rice tissues significantly, and thus enhanced the degradation of CrylAb protein within them. The degradation of CrylAb was significantly affected by soil microbe, water contents, pH value and temperature of soils. The soil microbe was determined as a primary factor affecting CrylAb degradation in paddy soils. CrylAb degradation rates were getting higher as the increase of pH value and temperatures under the experimental conditions.2. CrylAb content in Bt rice plant at varous growing stages, and degradation of CrylAb in plant in paddy habitatsBy using standard ELISA (Enzyme-linked immunosorbent) test kits of US EPA, the seasonal dynamics of Bt insecticidal protein expression in different plant tissues of two transgenic rice lines, KMD1 and KMD2, crylAb and the temporal and spatial patterns of CrylAb degradation and residue in the tissue litter, were determined in the greenhouse and paddy. The results showed that CrylAb was detected in all tissues of KMD, but its concentrations varied with the plant part and growing stages. From early tillering stage to mature stage, the concentrations of CrylAb in the stem, leaf and root of KMD1 were 3.74~ 7.50g/g, 3.78~9.13g/g and 0.51~0.56g/g, respectively, and those of KMD2 were 3.97~8.25g/g, 4.19~8.84g/g and 0.47~0.51g/g, respectively. The mean CrylAb concentrations in dry pollens of KMD1 and KMD2 were 13.12g/g and 31.40g/g, respectively. CrylAb in the root exudation of KMD1 reached 1.18~21.85 ng/plant-d. At 160d after harvest, the mean concentrations of CrylAb in tissue litter and root of KMD1 were 0.29g/g and 0.07g/g, respectively, and those of KMD2 were 0.38g/g and 0.09g/g, respectively. The concentrations of CrylAb at soil surface and root rhizosphere released from decomposition of tissue litter and root exudation were less than the limit of detection with 0.5ng/g fresh soil.3. Concentrations of CrylAb insecticidal protein in water released from Bt rice tissue litter and its impacts on aquatic insectsThe stems and leaves of KMD1 and KMD2 at late mature stage were submerged in water, and the CrylAb concentrations in these plant tissues as well in the water were determined. The population densities of major aquatic insect groups were surveyed at early, mid- and late tillering stages of Huachi 6 and Jiazao 935.