Soluble fragments from fungal cell walls elicit defence reactions in crayfish

Abstract

ALTHOUGH most fungi that parasitise arthropods are relatively harmless, many can penetrate different types of cuticle1. Thus active defence mechanisms presumably operate in vivo. In crayfish, for example, resistance to fungal penetration is associated with melanisation of the cell wall of the fungus by host phenols and phenoloxidase2. This constitutes a system for recognising the invading organism at different levels, from the cuticle surface inwards3. Melanisation in insect blood, due to phenoloxidase activity, is also induced by the presence of cells or cell walls of fungi4,5. Crayfish phenoloxidase in cuticle and blood is highly and specifically activated in contact with the purified hyphal cell walls of most fungi but not with other plant cell walls6. We have now found that soluble β-l,3-glucans from fungal cell walls activate the enzyme and may serve as specific elicitors of recognition in crayfish of invading fungal parasites.