Distribution and appearance of alfalfa mosaic virus in infected plant cells

Abstract

A virus isolated from Capsicum annuum L. was identified by host range, electron microscopy, and serology to be alfalfa mosaic virus (AMV). This isolate of AMV contained at least four components, Ta, Tb, M, and B with lengths 25, 40, 55, and 64 mμ, respectively. When subjected to high speed centrifugation, components Tb and M formed small crystalline arrays in the virus pellets. Similar crystalline AMV structures were found in some mesophyl cells of Capsicum, in sharply delimited epidermal areas of Vigna, but not in Nicotiana, where abundant uncrystallized virus was observed in the cytoplasm of infected cells. Measurements of AMV in the different hosts were compared with measurements of partially purified AMV. Components Tb and M were the only two components that could be recognized with certainty in the different hosts. We argue that the crystalline appearance of AMV in Capsicum and Vigna is a result of the loss of compartmentalization of certain basic proteins and some divalent cations that cause crystallization of AMV in vitro. The virus infection is responsible for a host reaction (necrosis) that results in loss of compartmentalization of these compounds. In Havana 38 tobacco, no necrosis occurred and no aggregation was observed. No change in component composition of the AMV population was detected after two passages through each of the three hosts.