Antiviral Activity of the Glucan Lichenan (Poly-β(→ 3,1 → 4)D-anhydroglucose). 2. Studies on the Mode of Action

Lichenan a ^{ 1 -• 3,1 -> 4}-^-glucan exhibited a broad antiviral activity against mechanically transmitted viruses of different taxonomic groups in different Nicotiana spp. As shown for tobacco mosaic virus in vitro, lichenan did not interfere with cell-free protein synthesis programmed with naked RNA or virus particles cotranslationally disassembled. Thus, inhibition of virus replication by lichenan is probably not attributed to direct interaction of lichenan and viral structural components, but rather to reduced sensitivity of the host tissue. Treatment of a suspension of cultured cells of Nicotiana tabacum with lichenan was accompanied by a slight increase in phenylalanine ammonia-lyase (PAL) activity. However, lichenan applied to leaf tissue did not significantly stimulate PAL-activity, therefore, antiviral action apparently did not depend on the induction of the phenylpropanoid pathway. According to experiments with lichenan and digitonin (used as a callose elicitor) restriction of viruses to initially-infected cells by means of caliose deposition also appears to be an improbable mechanism of viral inhibition. In cell suspensions treated with lichenan, slight changes in the extracellular concentration of free K* were observed that did not reflect a marked K* leakage, as caused by digitonin. This finding requires further examination. According to the present results, it is likely that lichenan affects the early virus-cell interactions that occur after virus disassembly