Antiviral Activity of the Glucan Lichenan (Poly‐β(l→3, 1→4)D‐anhydroglucose)

Lichenan is a linear glucan of (1→3, 1→4)‐β‐glycosidic bonds in a ratio cf 1:2 that originates from the lichen Cetraria islandica . Lichenan at 5–1000 μg/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 accumulation in greenhouse‐grown Nicotiana tabacum (four cultivars), N. benthamiana and N. glutinosa . In plants of N. tabacum cv. “Xanthi‐nc”, which react hypersensitively in response to TMV infection, lichenan reduced the number, but not the size, of necrctic 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 frotn a plant‐specific protection, which does not function in N. rustica . Although less inhibitory than lichenan, there were other mixed‐linkage β‐glticans (schizophylian, pacbytnan, laminaran, barley‐β‐glucan) causing antiviral effects. In contrast, pustulan as well as glucans of the a‐coniiguration (amyiose, dextran, nigeran, puUulan) were ineffective.