Modification of plastid ultrastructure in tomato leaf cells infected with tobacco mosaic virus.

Abstract

Tomato ( Lycopersicon esculentum var. High Pigment Beta) seedlings were inoculated with a common strain of tobacco mosaic virus (TMV). Leaves produced after inoculation and displaying typical TMV symptoms were fixed in glutaraldehyde/acrolein followed by osmium tetroxide; care was taken to process the different-colored portions of the leaves separately. In yellow areas of the leaf both “normal” and abnormal plastids were found. The abnormal plastids were compared with control plastids from uninoculated plants. Three general types of abnormal plastids were encountered and have been characterized as “supergranal,” “thylakoidal,” and “reticulate.” The abnormal plastids were often enlarged and sometimes showed large accumulations of osmiophilic bodies and/or peculiar membrane configurations; many of these were morphologically similar to mutant plastids reported in the literature. Both abnormal and “normal” plastids were found in single “mixed” cells; in fact such phenotypic variation seemed to be characteristic of the palisade parenchyma cells in the yellow areas of the infected leaves while it never was found in controls. Many “mixed” cells also exhibited masses of TMV particles as well as other inclusions characteristic for TMV infections. These results are discussed in the light of other research on plastids found in mutants, experimental treatments, and viral diseases.