| In the part of tobacco-producing areas of our country, the tobacco alkaloid content of tobacco leaves is very high, which affects the availability of tobacco seriously as well as plagues the tobacco industry and agriculture continually. On the ground of the fact that topping serving as mechanical injury stress can effectively activate the system defense responses of tobacco plants and further inducing roots to produce tobacco alkaloids substantially and accumulate in the leaves ultimately. In this paper, basing on the previous studies of our laboratory, the bionics signal molecule (BSM) tracing from the oral secretion of tobacco feeding oligophagous pests was applied to the top of tobacco caulis after topping in order to study the interaction effects of bionics signal molecule and the factors, such as topping period, application time of BSM and tobacco varieties so that it provided reliable reference for making use of BSM to control the content of tobacco alkaloids at a appropriate level.The main aspects of the degree paper are summarized as follows:1. The effect of bionics signal molecule (BSM) on flue-cured tobacco alkaloids was analyzed after different topping periods and usage time by Solid Phase Extraction and High Performance Liquid Chromatography. The result showed that after application of BSM to tobacco of initial-bloom and full-bloom topping, the decrease rate of total alkaloids of initial-bloom topping treatment was higher than that of full-bloom topping treatment and the alkaloids content of the former was lower than the later. Both of the two topping disposes could make percentage of nicotine higher and trace alkaloids lower. The application of BSM in an hour after decapitation not only decreased the content of alkaloid and percentage of trace alkaloids, but also enhanced percentage of nicotine. In general, the effect of BSM of different application time on alkaloids after topping by order of small to large was 1h>3h>5h..Therefore, the effect of BSM on flue-cured tobacco alkaloids was more marking in an hour after initial-bloom topping treatment.2. Total alkaloids accumulation dynamics on roots, leaves and stalks of flue-cured tobacco and burley tobacco was determined and analyzed in the whole growth process. The result showed that before topping the total alkaloids content of root was higher than that of leaves and stalks, while the total alkaloids content of leaves, especially in the upper leaves, was much higher than that of roots and stalks after topping. Whether before topping or after topping, the total alkaloids content of stalks was lowest in the whole growth process of tobacco plants. The total alkaloids content fell by an average of more than 20% when BSM was employed to tobacco plants after topping. The effect of BSM to upper leaves of flue-cured tobacco was obviously higher than that of middle leaves, but the result of BSM to upper leaves of burley tobacco was obviously lower than that of middle leaves. Reduction rate of BSM to roots and stems differed according to various growth processes, which peaked at the fifth day as for flue-cured tobacco and the fifteenth day as for burley tobacco. In general, the fall rate of total alkaloids after using BSM manifested leaves>toots>stems.3. The activity of lipoxygenase (LOX) and ornithine decarboxylase (ODC) of different treatment tobacco plants were determined so as to revel the possible mechanism that BSM could lower the tobacco alkaloids content of tobacco plants after topping. The LOX variation trend of topping and applying BSM resembled that of mere topping; both of them initially raised gradually, peaking at 6 h, then reducing little by little and coming to the level of the contrast; moreover the activity of LOX after BSM treatment was 7.81 U·g-1FW·min-1 which was restrained evidently, reducing to 75% of no BSM treatment at maximum value in 6 h. The ODC variation trend was similar to that of LOX; but the time of ODC peak was later than that of LOX, which separately was 41.12 CO2/g-1FW·min-1 and 36.50 CO2/g-1FW·min-1 at twelfth hour after topping. Then the activity of LOX descended laggardly, but in 48 h both of them were higher that the activity of the contrast.
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