Immunocytochemical Localization of Hydroxyproline-rich Glycoproteins in Tomato Root Cells Infected byFusarium oxysporumf. sp.radicis-lycopersici: Study of a Compatible Interaction

Abstract

The accumulation of hydroxyproline-rich glycoproteins (HRGPs) in cell walls of dicotyledonous plants has been correlated with a general defense mechanism against pathogenic attack. An antiserum raised against purified melon HRGPs was found to cross-react specifically with HRGPs from tomato. This antiserum was used to study, by immunogold cytochemistry, the subcellular localization of these glycoproteins in tomato root tissues infected by Fusarium oxysporum f. sp. radicis-lycopersici. HRGPs were found to be present in low amounts in healthy plant cell walls and were not detected in cultured F. o. radicis-lycopersici. Cell walls of infected tomato root tissues, especially those harvested between 96 and 120 hr after inoculation, were markedly enriched in HRGPs. Accumulation of these glycoproteins appeared to be initiated after contact between the pathogen and the plant cell wall and to occur as a result of tissue damage. Although HRGPs were detected in wall apposition formed in the cortical area in response to infection, their restricted occurrence in walls of invaded cells showing signs of pronounced alteration suggests that accumulation of HRGPs in susceptible tomato plants is a late biochemical event. This supports the concept that early enhancement of HRGPs is a prerequisite to their efficiency in the protection of plants.