Viral and host RNA synthesis in BSMV-infected barley

Abstract

BSMV (barley stripe mosaic virus) nucleoprotein, BSMV-RNA (ribonucleic acid), and host RNA synthesis were characterized in the mature, inoculated leaf one and the systemically infected leaf two at 24-hr intervals from 1–8 days after inoculation. BSMV-RNA synthesis preceded virion appearance by approximately 24 hr in either leaf. In leaf one, viral RNA synthesis was occurring by 24 hr after inoculation. An excess of up to 150-fold of viral RNA was apparent during early stages of virion accumulation. During periods of rapid viral RNA accumulation, the in vivo rate of 32P incorporation into viral RNA was much higher than into host RNA in infected tissue or in comparable healthy tissue. Host RNA synthesis was reduced during or after periods of rapid viral RNA accumulation, as determined by 32P-labeling. The quantity of sedimenting host RNA was also reduced. The maximum level of viral RNA was comparable in either leaf, but the systemically infected leaf two produced about three times the amount of viral nucleoprotein as did leaf one. The severe inhibition of host RNA synthesis in leaf one may be one of the factors which results in the low “efficiency of encapsidation” in leaf one.