Abstract :
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
