Detection of Antigens of Powdery Mildew, Erysiphe graminis f.sp. Hordei, in Susceptible Plant Host Cells, Shortly After Inoculation and During the Early Stages of Infection

A polyclonal antibody directed against antigens on the surface of the germinated conidia of Erysiphe graminis f.sp. hordei E. M. Marchal was used to determine the presence and location of these antigens in host (barley) tissues from 4 to 96 h after inoculation. These studies were carried out using protein A-gold immunolabeling followed by quantitative analysis of labeling density in the nuclei, chloroplasts, vacuoles, and walls of the host cell. Four hours after inoculation the level of labeling detected in mesophyll cells of infected tissues (which are not penetrated by the fungus) was similar to that found in control healthy tissues. However, at 24 h and especially at 96 h after inoculation, the level of labeling in infected tissues was significantly higher than in the healthy tissues. This increase in labeling in infected tissues may be a result of synthesis of co-antigens by the plant as a response to infection, or it may indicate that fungal antigens enter the mesophyll cells very early in the infection process (4-24 h) around the time that penetration of the epidermal cell by the infection peg occurs.