Antiviral Activity of the Glucan Lichenan (Poly-β(l→3, 1→4)D-anhydroglucose). 1. Biological Activity in Tobacco Plants

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