Efeito de um inibidor de proteinase serinica sobre o desenvolvimento e atividade enzimatica de Heliothis virescens (Lepidopter: Noctuidae) / Effect of a trypsin inhibitor on the development and enzymatic activity of Heliothis virescens (Lepidoptera: Noctuidae)




Proteinase inhibitor proteins (PIs) are one of the defensive chemicals produced by plants against pests and pathogens. PIs are polypeptides that are able to bind to insect midgut proteolytic enzymes, rendering them inactive by competitive inhibition. This process leads to a limitation of essential amino acids in protein synthesis, and thus, to reduction in growth and development. Therefore, PIs are known as antinutritional factors. The tobacco budworm, Heliothis virescens (Fabr., 1781) (Lepidoptera: Noctuidae) is a polyphagous insect larvae that is principally a field crop pest, attacking such crops as alfalfa, cotton, soybean and tobacco. However, it sometimes attacks such vegetables as cabbage, lettuce, pea, pepper, pigeon pea, squash, and tomato, especially when cotton or other favored crops are abundant. In this report, the pure inhibitor from seeds of Adenanthera pavonina L. (Mimosaceae) - ApTI was monitoring by an insect bioassay its insecticidal activity toward H. virescens. The in vitro inhibitions of proteinases activities by ApTI suggest that ApTI would have a potential antimetabolic effect when ingested by insect larvae. However, chronic ingestion of ApTI did not result in a significant reduction of growth and development of tobacco budworm. No differences in larval mortality, weight gain, larval and pupal developmental time were observed. To study this adaptation, the midgut proteinases of H. virescens larvae reared on artificial PI-free diet and on a diet containing ApTI at 0.4% were compared by using enzymatic assays and polyacrilamide gel electrophoresis. The fourth instar larvae reared on a diet containing ApTI showed a 2-fold increase in tryptic activity, as confirmed by BApNA as substrate and by activity in gels. In addition, the tryptic activity in ApTI-fed larvae was less sensitive to ApTI, indicating that novel proteolytic form resistant to ApTI was induced in larvae reared on a diet containing this inhibitor. These results suggest that H. virescens larvae were able to physiologically adapt to inhibitor by overproduction of an existing trypsin-like enzyme and production of a new type of trypsin-like enzyme that is less susceptible to inhibitory action of ApTI.


trypsin inhibitors inibidores de tripsina adenanthera pavonina adenanthera pavonina heliothis virescens inseticidas insecticides heliothis virescens

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