Surface Characteristics of Root and Haustorial Hairs of Parasitic Scrophulariaceae

The outer wall surfaces of root and haustorial hairs in seven species of parasitic Scrophulariaceae were examined with scanning electron microscopy. The surface of nonhaustorial root hairs is comparatively smooth and free of extracellular coating material; that of haustorial hairs is coated with an extracellular matrix, which has a granular or papillate appearance. Haustorial hairs of attached haustoria show an increased amount of the coating material over that observed for haustorial hairs of nonattached haustoria. Haustorial hairs directly involved in host attachment have the greatest amount of coating material. At the attachment interface between parasite and host, the coating material forms a continuous sheet, thereby enhancing adhesion of the haustorium to the host root by increasing the effective area of contact.