Interface between haustoria of parasitic members of the Scrophulariaceae and their hosts: a histochemical and immunocytochemical approach

The haustorial structure of three African parasitic members of the family S crophulariaceae (Buchnera hispida, Rhamphicarpa fistulosa, and Striga hermo nthica) has been studied with regard to the interface between haustoria and the invaded host roots. Immunocytochemical observations at the light and e lectron microscopical level were carried out with monoclonal antibodies aga inst pectin, JIM5, JIM7, and hydroxyproline-rich glycoprotein (HRGP), LM1. Lignins have been visualized by phloroglucinol-hydrochloric acid staining. At the margin of the lateral interface (contact area of host root cortex an d parasite cells), JIM5- and JIM7-labelled substances accumulate between pa rasite papillae and the host root surface indicating that pectins are impli cated in sealing the parasite to the attacked host organ. The lateral inter face is characterized by the presence of compressed, necrotic host cells, w hereas the central interface (contact area between host stele and parasite cells) is generally devoid of host cell remnants. Phenolic substances and/o r lignins can be found at the site of penetration of the haustorium into th e host root. These observations and the fact that HRGPs accumulate at the h ost side of the interface support the view of, at least, a partial defense reaction in the invaded host root tissues. Within haustoria, HRGPs were res tricted to differentiating xylem elements, implying a spatio-temporal regul ation of HRGPs in developmental processes.