Isolation and Characterization of a Virus Inhibitor from Spinach (Spinacia oleracea L.)

A virus inhibiting protein (VI) was isolated from spinach (Spinacia oleracea L.). The VI inhibited infections of test plants with plus- and minus-strand RNA viruses. Inoculation of both local lesion and systemic hosts with TMV in the presence of varying amounts of the VI resulted in typical dose response curves for the number of local lesions or the amount of virus respectively. The lowest concentration of VI leading to a significant reduction in the number of local lesions was 0.06 μg/ml. The VI was found to inhibit local lesion formation only when applied within 2–3 h p.i. but still reduced the number of local lesions when applied up to 9 h prior to virus inoculation. The antiviral activity could be attributed to a protein of molecular weight 29,000 dalton with an isoelectric point of 10.3. Its activity was destroyed by heating for 30 min to 70°C. These characteristics resemble those of other virus inhibiting proteins described for members of the order Caryophyllales such as the Phytolacca inhibitor against which a serological relationship was obtained.