Abstract :
Lichenan is a linear glucan of {1 ->3, I ->4}-/i-glycosidic bonds in a ratio
of 1:2 that originates from the lichen Cetraria lilandica. Lichenan at 5-
1000 /ig/ml exhibited antiviral activity against mechanically-transmitted
viruses of different taxonomic groups. The antiviral activity was demonstrated
by the inhibition of symptom development and virus accnmulation
in greenhouse-grown Nicotiana tahacum (four cultivars), N.
benthamiana and N. glutinosa. In plants of Aʹ, tahacum cv. ʹXanthi-ncʹ,
which react hypersensitively in response to TMV infection, hchenan
reduced the number, but not the size, of necrotic lesions both, when
added to purified virions or naked viral RNA. Partly hydrolized
lichenan representing different degrees of polymerization (DP) of 6-30,
30-60, 60-190, and > 190, reduced the number of local and systemic
infections to the same degree as the unchanged glucan. The antiviral
effect of lichenan was restricted to the leaf-area of application. Depending
on the time of application, the strongest effect was achieved when
lichenan was added directly to the inoculum. Post-infectionally, it was
inhibitory only up to 3 h post-inoculation, indicating that early events
of virus replication were affected. Viral inhibition caused by lichenan
results from a plant-specific protection, which does not function in Aʹ.
rustica.
Although less inhibitory than lichenan. there were other mixed-linkage
^-glucans (schizophylian, pachyman, laminaran, barley-^-glucan)
causing antiviral effects. In contrast, pustulan as well as glucans of the
a-configuration (amytose, dextran, nigeran, puUulan) were ineffective
