VIEW ARTICLE

Physiology and Biochemistry

The Role of Cytoplasmic Mycolaminaran in Inhibiting Initial Viral Infection of Certain Nicotiana species. Thomas M. Zinnen, Plant Molecular Biology Center and Department of Biological Sciences, Northern Illinois University, DeKalb 60115; Christina M. Heinkel, M. E. S. Hudspeth, and R. Meganathan. Plant Molecular Biology Center and Department of Biological Sciences, Northern Illinois University, DeKalb 60115. Phytopathology 81:426-428. Accepted for publication 8 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-426.

The effect of mycolaminaran, a ?-1,3-glucan purified from the cytoplasm of Phytophthora megasperma, on initial infection by tobacco mosaic virus of Nicotiana species was tested. When mixed at 62–1,000 ?g/ml with TMV inoculum and applied to Nicotiana tabacum ‘Xanthi-nc’, mycolaminaran reduced necrotic local lesion numbers by as much as 98%. In contrast, laminaran, a mannose-containing glucan derived from an alga, reduced infection by only 40–75%. Mycolaminaran did not reduce initial viral infection of Nicotiana rustica. This established that the polysaccharide inhibited infection but did not inactivate the virus. Mycolaminaran inhibited infection by TMV RNA as well as by TMV virions, indicating that viral infection was blocked at a stage after uncoating. When applied 4 h after inoculation, however, mycolaminaran did not reduce the number of viral lesions. Therefore, the affected stage was early in infection. The glucan also inhibited TMV infection in N. tabacum ‘Xanthi’ that lacked genes for necrotic reaction with TMV, establishing that such genes were not required for the observed inhibition. We found no evidence, however, for any systemic resistance induced by mycolaminaran. These results are consistent with the hypothesis that mycolaminaran specifically and rapidly induces a general resistance in certain plants to local viral infection on leaf surfaces treated with the glucan.