The Fate of the Transport Protein of Tobacco Mosaic Virus in Systemic and Hypersensitive Tobacco Hosts

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Abstract
The transport protein of tobacco virus (TMV) (Mr 30,000, 30K non-structural protein) was detected on Western blots, using an antiserum to a synthetic C-terminal nonapeptide. Accumulation of this protein in subcellular fractions of inoculated leaves was measured during TMV infection of Nicotiana tabacum cv. Samsun and cv. Samsun NN. In cv. Samsun, a systemic host, the 30K protein appeared transiently in a crude membrane fraction but accumulated more stably in cell walls. In cv. Samsun NN, which is a hypersensitive host giving only localized infection, the early accumulation (up to 40 h; before any necrosis was visible) was the same as in cv. Samsun. However, as soon as necrosis was visible, the amount of 30K detected in the cell wall fraction decreased sharply and coat protein synthesis stopped. This drop in the amount of 30K protein is most easily interpreted as a side-effect of the hypersensitive reaction and may explain why TMV infection becomes localized in leaves of cv. Samsun NN.