Abstract
Mesophyll protoplasts of barley were efficiently infected with brome mosaic virus (BMV) in two different ways under different conditions. Polycation-independent infection occurs at low pH in low ionic strength inoculum whereas polycation-dependent infection occurs at high pH in higher ionic strength inoculum. Optimal conditions at low pH were 20 µg/ml BMV, 0.2 µg/ml poly-L-ornithine and 0.7 M-mannitol in 0.1 mM-potassium citrate buffer, pH 5.0; about 70% of protoplasts were infected. Optimal conditions at high pH were 1 µg/ml BMV, 1 µg/ml poly-L-ornithine and 0.7 M-mannitol in 50 mM-phosphate buffer, pH 8.8; nearly 60% of protoplasts became infected. A brief contact of virus and poly-L-ornithine was essential for infection at high pH whereas it inhibited polycation independent infection at low pH. At high pH, poly-L-ornithine formed aggregates with virus. Infection of protoplasts seemed to be controlled by the strength of the positive charge on virus particles at low pH and that on the virus-poly-L-ornithine complexes at high pH.