Potencial de inibidores serinicos em folhas de Croton urucurana (Malpighiales, Euphorbiaceae) para o controle de Spodoptera frugiperda (Lepidoptera, Noctuidae)

Abstract

The maize crop is one of the principal and most economically important in Brazilian agribusiness, but its productivity is still considered low when compared to some developed countries. One of the major factors that prevents more expressive numbers in the harvest is the high pest incidence in the crop, especially the fall armyworm (Spodoptera frugiperda, Lepidopterae, Noctuidae). The adaptive mechanisms of this polyphagous pest ensure its acquisition of resistance to several chemical compounds after a few generations, making it difficult to control. On the last decades the tendency on bioprospection of natural molecules focused on pest control have largely increased, especially the proteinaceous compounds that constitutively participate on the plant defense mechanisms. In consequence, several researches with plant peptidase inhibitors (PPIs) are highlighting their insecticidal activity, it reduces the availability of essential amino acids to the growth of the larva, leading to death. In this work, we’ve bioprospected leaf extracts of Croton urucurana, a plant traditionally known by its medicinal properties and native of the Brazilian Cerrado, a biome considered as a hotspot of biodiversity where plants have developed particular mechanisms to resist and survive in extreme environmental conditions. The extracts were prepared in Tris-HCl buffer (50 mM) and acid buffer (1000 mM HCl).The extracts in Tris were precipitated with ammonium sulfate at distincts saturations, F1(0-30%), F2 (30-60%) and F3 (60-100%). The protein profile analysis was performed by SDS-Page 12% electrophoresis and total protein determination of the extracts and precipitated by the Bradford methodology. A preliminary enzyme assay was performed using the non-specific substrate Azocasein (1%) and Trypsin Bovine. Upon finding higher antitryptic activity in the F2, we proceed an specific substrate assay using BApNA (1.25 mM) in bovine trypsin. When significant inhibitory activity was observed, the BApNA substrate assay was performed in intestinal homogenate of S. frugiperda, which returned 80% of inhibitory activity when 2.7 μg.mL- 1 of the extract was used. Although new steps are required involving the fractionation and purification of the PPI, the results obtained prove the insecticide potential of the plant and point to the possibility of a biotechnological product destined to the control of Lepidoptera.