IN-SITU LOCALIZATION OF BARLEY YELLOW DWARF VIRUS COAT PROTEIN IN OATS

The expression of barley yellow dwarf virus (BYDV) coat protein was fo llowed in situ by immunogold labeling of ultrathin sections. Samples o f BYDV-PAV-IL-infected oat seedlings were taken 1-10 days postinoculat ion (dpi) and prepared for electron microscopy. Gold labeling was firs t detected in the host cytoplasm at 2 dpi. At 3 dpi, labeling had incr eased and was found mostly around or within regions that contained rib osome-associated filamentous material. No labeling was found over dens ely compressed filaments. By 4-5 dpi, viral coat protein also was dete cted in the nucleus, Viral coat protein was not associated with any ot her cellular components. The results suggest that viral coat protein i s first expressed in the cytoplasm of the infected host cell. Since la beling was mostly found in or around regions of ribosome-associated fi laments, it is proposed that coat protein is expressed by cytoplasmic ribosomes from viral RNA. Coat protein found in the nucleus during lat er stages of infection probably diffused into the nucleoplasm after di sruption of the nuclear membrane.