Infection of Barley by Brome Mosaic Virus Is Restricted Predominantly to Cells in and Associated with Veins through a Temperature-Dependent Mechanism

Results from previous cytological studies on barley (Hordeum vulgare) infected with brome mosaic virus (BMV) indicated that this virus can infect and accumulate to high levels in mesophyll and other cell types within the leaves. Through immunocytochemistry and in situ hybridization, we have determined that BMV infection in barley is restricted predominantly to cells within and associated with vasculature when plants are grown at 24/20°C (day/night). This tissue restriction can be fully overcome by growing infected plants at 34°C for 2 h. Our results also indicate that BMV is likely to start systemic infection of young, uninoculated leaves in barley before spreading into all longitudinal veins in inoculated leaves. Possible barrier(s) to BMV movement between vascular bundle sheath cells and mesophyll cells, and the relationship between virus and photoassimilate transport through longitudinal and transverse veins are discussed.