Turn The Bt Corn Leaf Microflora And Research On The Laws Of The Bt Protein Expression

With the large scale release of transgenic crops, their possible ecological risks have beenpaid an increasing attention. Transgenic maize containing gene to produce the insecticidal toxinhas been widely planted. Most research on Bt maize has focus on invasiveness, gene flow toindigenous organisms, development of resistance in target pests, and direct or indirect effects onnon-target organisms and ecosystem. A few studies have been published to evaluate theecological effects of Bt maize on epiphytes. The aerial habitat colonized by these microbes istermed the phyllosphere, and the inhabitants are called epiphytes. While there has been someinvestigation of the colonists of buds and flowers, most work on phyllosphere microbiology hasfocused on leaves, a more dominant aerial plant structure. Bacteria are by far the most numerouscolonists of leaves, often being found in numbers averaging 106to 107cells/cm2(up to 108cells/g) of leaf. Because of their numerical dominance on leaves, and because more informationis available on the process of bacterial colonization of leaves, we focus on this group of microbesin this review. Therefore, in this study impact of Bt maize on the diversity of epiphytescommunities under field conditions is evaluated for the ecological risk of Bt maize.The transgenic Bt maize MON810 and non-transgenic maize were grown in field condition(The Ministry of Agriculture, genetically modified plants Environmental Safety Supervision,Inspection and Testing Center special test base) for two years from 2010 to 2011.The leaves ofmaize seedling stage, jointing stage, trumpet stage, tasseling stage, silking stage, milking stageand full-ripe stage were examined. Epiphytes community diversity and functional diversity undernatural conditions were analyzed to make out whether the maize genotypes affect thephyllosphere microbes. The main research methods were the Biolog micro-plate method and thetraditional isolation culture methods. Enzyme-linked immunosorbent assay (ELISA) was alsoused to detect the Bt protein.1 The traditional separation of culture results showed that although there were differencesin the colony-forming unites of culturable bacteria, actinomycetes and fungi of phyllospherebetween Bt maize and non-Bt maize in different growing periods and different years, the trend ofannual differences was basically consistent at the same growth period: the quantity of microbesin seeding stage is fewest and reaches the peak in the late of growing period. Compared with the controls, transgenic Bt maize seemed to stimulate the reproduction of phyllosphere fungi.However, no significant effect on the populations of actinomycete was observed. Significantdifferences were detected for bacteria at jointing stage, trumpet stage, silking stage and milkingstage. In 2010，the Shannon-Wiener index, Simpson index and evenness index of bacteriaphysiological groups were higher at seeding, jointing and full-ripe stage, but lower at trumpetstage, tasseling stage, silking stage and milk stage. In 2011, the population characteristicparameters of the microorganisms of Bt-corn are more than the ones of non-Bt corn in the wholegrowing period except trumpet stage. It may be concluded there was some difference in terms ofimpacts between transgenic maize and non-transgenic maize，while the main impacts onmicrobial community composition were likely due to different years and different growthperiods．2 Biolog method was used to find the difference of carbon used by non-Bt maize and Btmaize, and to study the microbial differences of the metabolic functions of microbial activity inresponse to whether the influence by the Bt maize or not. The results showed that the activity ofPhyllosphere microorganism was weakest at seeding stage, highest at silking stage, and declinedat full-ripe stage. The carbon sources utilization ability of microorganisms on the Bt maizeleaves higher than that on the non-Bt maize leaves. The main carbon sources of epiphytes werecarbohydrate and its derivatives, while intermediate and secondary metabolites were used least.In the whole growth period, the Shannon functional diversity index and richness index of Btmaize were higher than non-Bt maize: compared with non-transgenic maize, transgenic maizehad less effects on Shannon functional diversity index, and richness index of Phyllospheremicrobes at seedling, silking and full-ripe stages, but had significant influence (P<0.05)ondiversity and richness index at trumpet stage. There were no significant difference been found inShannon evenness index and Simpson index during the whole growth stages. Principalcomponent analysis (PCA) indicated that there existed greater differentiation in the carbonsource utilization by the microbes on leaf surface of non-transgenic and transgenic maize atfull-ripe stage, suggesting the significant difference in the carbon source utilization pattern of themicrobes at this stage.3 The diversity of soil microbial community and utilization pattern of different carbonsources were assessed via Biolog method on the 10th, 25th, 40th and 55th day of transgenic Bt maize leaves decomposition. The results showed that there were no differences in soil microbialcommunity with ground leaves evennness, diversity, and concentration index between transgenicBt maize and no transgenic Bt maize on the 25th, 40th and 55th. Compared with non-transgenicmaize, transgenic maize had a higher influence (P<0.05) on soil microbial community ondiversity and evenness index at tasseling stage, but a lower influence (P<0.05) on simpsonconcentration index at milking stage. Principal component analysis indicated that transgenic Btmaize ground leaves had a obviously effects on indigenous soil microbial community structureand function on the 10th. It, however, had no effects on soil microbial community on the 55th.4 Temporal and spatial dynamic of Bt gene expression in Bt transgenic maize was studiedby testing the Bt crystal toxin protein in different growing stages and tissues of plant. The resultsshowed that with the growth of Bt maize, the proportion of Bt protein to total soluble proteins inleaves, stalk, filament, tassel stalk, tassel florets and female corncobs continuously increased.Ingeneral, the contents and proportion were lower in the young tissues or organs, but higher in themature. The correlation analysis showed that, the content of Bt protein was positively related toBt maize growth periods. The insecticidal crystal proteins has no significant infuence onepiphytes, and it has a lower infuence on epiphytes compared with growing stages.