Ultrastructural and biochemical basis of the digestion of nectar and other nutrients by the moth Erinnyis ello
1990
The midgut epithelium of adult Erinnyis ello L. (Lepidoptera: Sphingidae) forms ramified villus-like folds. The epithelial cells exhibit long microvilli and narrow and sinuous basal channels studded with particles. These morphological features are thought to be involved in the absorption of nutrients present in low concentration in food. Enzymatic assays in E. ello adults showed the presence of amylase in salivary glands, and the occurrence of aminopeptidase, β-fructosidase, α- and β-glucosidase, trehalase and trypsin in the midgut. Calcium differential precipitation of midgut homogenates showed that aminopeptidase and α-glucosidase are integral proteins of the microvillar cell membranes, whereas the other enzymes are soluble or partly soluble and partly membrane bound. Detergent-solubilized aminopeptidase (pH optimum 7.5) sediments as a protein with Mr 120000, whereas trehalase (pH optimum 6.5), as a protein with Mr 95 000. The activities of amylase (pH optimum 5.5), β-glucosidase (pH optimum 5.0) and trypsin (pH optimum 9.5) were not sufficiently high to be further characterized, whereas β-fructosidasc and membrane-bound α-glucosidase were characterized elsewhere. The data suggest that nectar-feeding E. ello adults are able to some extent to digest and absorb starch and proteins, in addition to nectar sugars. Initial digestion is considered to occur in midgut lumen and final digestion on the surface of midgut cells under the action of microvillar enzymes.
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