No description available.

One of the means whereby an insect recognises a plant is "by detecting secondary plant compounds. Some such compounds are phagostimulatory but many act as feeding deterrents. The extent to which these deterrents are toxic was investigated in this thesis using Locusta migratoria, an oligophagous species which feeds mainly on grasses and thereby avoids many secondary plant compounds and Schistocerca gregaria, a polyphagous species which feeds on many plants deterrent to Locusta. Toxicity tests revealed that single injections of azadirachtin, allyl isothiocyanate, tomatine and nicotine into the haemolymph were significantly more toxic to Locusta than to Schistocerca. Sinigrin, umbelliferone and salicin were non-toxic in the short term to both species. Overall there was a significant positive correlation between the deterrency of the compounds to the insects and their toxicity. Tolerance was greater following cannulation of the compounds into the gut where only allyl isothiocyanate and nicotine were toxic to Locusta, and Schistocerca was unaffected by all the test compounds. Sinigrin is more deterrent to Locusta than to Schistocerca yet in the short term was non-toxic to both species. Long term feeding studies, in which the formulation of the test compound was shown to affect its toxicity, demonstrated however that Locusta was more susceptible to sinigrin than Schistocerca. Nicotine, which followed the overall pattern of being more deterrent and toxic to Locusta than to Schistocerca, was shown to be excreted from the haemolymph and voided from the gat more efficiently in Schistocerca. The target organs of Schistocerca were also less permeable to nicotine than those of Locusta. These factors, together with the ability of Schistocerca to induce its mixed-function oxidase system are suggested as the reasons for its greater tolerance to nicotine compared to Locusta . Azadirachtin is 1000 times more deterrent to Schistocerca than to Locusta, yet was more toxic to Locusta. Azadirachtin was shown to decrease body growth and increase the instar length in both species of insect. This effect is associated with a lack of feeding which could be caused by a direct toxic action to the gat as suggested by histological evidence. Gut contractions in Locusta were reduced 'in vitro' after application of azadirachtin. The inductive effect of azadirachtin on the mixed-function oxidase levels was greater in Schistocerca than Locusta. It is concluded that Locusta is physiologically less able to deal with secondary plant compounds than Schistocerca as a result of having evolved from a polyphagous to a graminivorous feeding strategy.

No description available.

No description available.

Under challenge by a dietary soybean cysteine protease inhibitor (scN), cowpea bruchids overcome the inhibitory effects by reconfiguring the expression profiles of their major digestive enzymes, the cathepsin L-like cysteine proteases (CmCPs). In addition, cowpea bruchids activate transcription of the counter-defensive cathepsin B-like cysteine protease (CmCatB). I undertook an interest in understanding the molecular mechanisms utilized by bruchids to differentially regulate cysteine proteases in response to plant inhibitors. First, to investigate the functional significance of the differential regulation of CmCPs, I expressed CmCP proprotein isoforms (proCmCPs) in E. coli, and characterized their activities. Among proCmCPs, proCmCPB1 exhibited the most efficient autocatalytic processing, the highest proteolytic activity, and was able to degrade scN in the presence of excessive CmCPB1. Second, to dissect the molecular mechanisms behind the differential function of CmCPs, I swapped domains between two representative subfamily members B1 and A16. Swapping the propeptides did not qualitatively alter autoprocessing in either protease isoform. Incorporation of either the N- or C-terminal mature B1 segment into A16, however, was sufficient to prime autoprocessing of A16. Bacterially expressed isolated propeptides (pA16 and pB1) showed that pB1 inhibited B1 enzyme less than pA16 due to its protein instability. Taken together, these results suggest that cowpea bruchids selectively induce specific cysteine proteases for their superior autoprocessing, proteolytic efficacy, and scNdegrading activities, and modulate proteolysis of their digestive enzymes by controlling cleavage and stability of propeptides to cope with plant inhibitors. Third, to understand the transcriptional regulatory mechanisms of CmCatB hyperexpression that underlies bruchid adaptation, I cloned a portion of its promoter and demonstrated its activity in Drosophila S2 cells using a CAT reporter system. Gel shift assays identified cowpea bruchid Seven-up (CmSvp, chicken ovalbumin upstream promoter transcription factor homolog) in scN-unadapted insect midgut, and cowpea bruchid HNF-4 (CmHNF-4, hepatocyte nuclear factor 4) in scN-adapted insect midgut. When transiently expressed in S2 cells, CmSvp repressed, while CmHNF-4 activated CmCatB expression. CmSvp antagonized CmHNF-4-mediated transactivation when they were present simultaneously in the cell. Thus, the data suggest that transcriptional regulation of CmCatB in response to plant inhibitor depends, at least partly, on the cellular balance between positive and negative regulators.

Title from PDF of title page (University of Missouri--Columbia, viewed on March 8, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Qisheng Song. Vita. Includes bibliographical references.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.