Ultrastructural changes and immunocytochemical localization of the elicitin quercinin in Quercus robur L. roots infected with Phytophthora quercina

Abstract

We report on the growth pattern of the root rot pathogen Phytophthora quercina in roots of oak seedlings and on the localization of its elicitin quercinin. Some hours after infection, the pathogen was mainly found in the intercellular spaces of the cortical parenchyma. Some parenchyma cells were also invaded by P. quercina and the plasmalemma of those cells as well as of neighbouring cells separated from the cell wall. Transmission electron microscopy studies proved that P. quercina penetrated the cell walls forming haustorial-like structures in invaded cells. These structures and cell wall appositions were covered with electron dense material. Immunofluorescence investigations in combination with a specific anti cryptogein antibody clearly showed that the P. quercina elicitin quercinin was located within the hyphal cell wall and seems to be released into invaded cells. In addition, immunogold labelling showed that quercinin was found in the intercellular spaces as well as in penetrated cells. Finally, we demonstrated with ELISA that quercinin was produced by the pathogen in infected tissue during the whole growth phase.