Isolation and characterization of a galactorhamnan polysaccharide from the seed coat of Canavalia ensiformis that is toxic to the cowpea weevil (Callosobruchus maculatus)

• Published in: Entomologia experimentalis et applicata 2001-12, Vol.101 (3), p.225-231
• Main Authors: Oliveira, A.E.A., Sassaki, G.L., Iacomini, M., da Cunha, M., Gomes, V.M., Fernandes, B.K.V.S., Xavier-Filho, J.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Biological control; Callosobruchus maculatus; Canavalia ensiformis; Control; cowpea weevil; Fundamental and applied biological sciences. Psychology; galactorhamnan; Jack bean; Phytopathology. Animal pests. Plant and forest protection; polysaccharide; Protozoa. Invertebrata; Protozoa. Invertebrates; seed coat
• ISSN: 0013-8703; 1570-7458
• DOI: 10.1046/j.1570-7458.2001.00907.x

We have isolated a water‐soluble polysaccharide from the Jack bean [Canavalia ensiformis (L) DC] seed coat that was shown to be highly detrimental to larval development of the cowpea weevil (Callosobruchus maculatus) (Coleoptera: Bruchidae). Determination of the composition and structure of this polysaccharide showed that it is a galactorhamnan with an Mw of 883.0, containing 92% rhamnose and 8% galactose. The polymer is formed by a main chain of rhamnose (1 → 2) substituted at O‐4 by galactose nonreducing end‐units. Immunolocalisation by light and electron microscopy showed that this polysaccharide is localised in the innermost cell layer of the seed coat and also in cotyledon tissues in the cytoplasm space. The presence of this toxic polysaccharide in the testa of a non‐host seed may have been important for the evolutionary discrimination of legume seeds by bruchids.