Protential Effects Of Midgut Proteinases In Chaphalocrocis Medinalis Larva To Adaot To Bt Toxin Protein

Rice leaf folder(Cnaphalocrocis medinalis Guenée) is one of the most destructive and widespread insect pests throughout the rice growing regions in the world. Bt(Bacillus thuringiensis,Bt) insecticidal genes have been successfully transferred into rice to control lepidopterans. Therefore, understanding of C.medinalis outbreak mechanisms is of important significance for sustainable control of the pest. This paper reviewed the occurrence and outbreak causes of the pest. Changes on the growth development and main enzymatic activities of C.medinalis midgut treated with low amount of Bt rice leaves over generations,character of midgut juice and its degradation to Bt proteins were studied to further understanding protential effect of mid-gut proteinases of C. medinalis larva in adapation to Bt protein Experimental results were shown as follows:1. Changes on the growth development and main enzymatic activities in midgut of Cnaphalocrocis medinalis intermittently treated with low amount of Bt rice leaves over generations.The developmental indices and main enzymatic activities in midgut of Cnaphalocrocis medinalis treated with low amount of Bt rice line T2A-1(harboring cry2 A gene) for three generations(treating for 5h every generation) were investigated for understanding the response abilities of C. medinalis against Bt rice. Results showed that developmental duration of 3rd-5th instar C. medinalis with the treatment in the 1st generation were prolonged and the emergence rates of C. medinalis in treatment in 1st generation sharply lowered compared with the untreated C. medinalis. However, these two indices recovered to the level of the untreated C. medinalis as the treated generations increased. The mortalities of the 3rd-5th instar C.medinalis larvae and the weight of female pupa lowered with the treatment in the 1st generation, and the the weight of male pupa did not differ in the treatment of the 1st generation compared with those of untreated C. medinalis. Furthermore, the mortality of the 3rd-5th instar C. medinalis larvae and weight of male and female pupa did not recover or remain the levels of the untreated C. medinalis as the treated generations increased, and the values of these indices in treatment of 3rd generation C. medinalis were lower than those of untreated C.medinalis. The total proteinase activities in C. medinalis larvae midgut juice in treatments were lower than that in untreated C. medinalis, but the total proteinase activity increased with the generations increased, and the similar trend was observed in the chymotrypsin-like enzyme activity of C. medinalis. While the activities of trypsin in the treated C. medinalis were higher than that in untreated C. medinalis and increased with treated generations increased, and the similar trend was observed in the aminopeptidase activity of C. medinalis.These results indicated that C. medinalis has potential adaptive ability when exposure to a low amount of Cry2 A protein. These results may play a potential role on the further studies on the evolution of the adaptability of C. medinalis to Bt protein.2. Characteristic of midgut juices in C.medinalis larvaeEffects of p H value and inhibitor on the activity of midgut enzymes juices in C.medinalis were valuated in this study. With different p H values of midgut enzymes juices, the activities of total proteinase and chymotrypsin-like increased as the p H value increased.Activity of trpsin-like did not affected by the p H value of midgut juice, while the highest activity was at 10.5 of p H value. The activities of total proteinase and chymotrypsin-like under reaction buffers with different p H values were with an increasing trend as the p H value increased, trypsin-like was with high activity when the p H value of reaction buffer was9.0-10.0. In the midgut juices treated with different inhibitors, the activities of total proteinase were significantly inhibited by PMSF、TLCK、Pepstatin A and Leupeptin; chymotrypsin-like activity was significantly inhibited by PMSF; trypsin-like activity was significantly inhibited by EDTA、PMSF、TPCK、TLCK and E-64.3. Degradation function of C.medinalis midgut juice to Bt proteinIn order to understand degradation function of midgut juice in C.medinalis larvae to Bt protein, the effect of p H value and inhibitor were evaluated on the degradation function of midgut juice to Bt protein(Cry2A、Cry1C、Cry1Aa、Cry1Ac). Results showed that p H value and inhibitors could affect the degradation function of midgut juice to Bt protein at a certain levels. When the p H value of midgut juices at 8.0- 10.5, midgut juices had high degradation function to Bt proteins. Different inhibitors had different degradation function to Bt proteins.EDTA could significantly inhibit the degradation of C. medinalis to Cry2A; EDTA, PMSF,TPCK, and TLCK could inhibit the degradation of C. medinalis to Cry1C; EDTA, PMSF,TPCK, and TLCK could inhibit the degradation of C. medinalis to Cry1Aa; EDTA、PMSF、TPCK、TLCK、E64 could inhibit the degradation of C. medinalis to Cry1 Ac.