An ultrastructural study of particle distribution during microsporogenesis in tomato plants infected with the Brazilian tobacco rattle virus

Abstract

Long and short particles of the Brazilian tobacco rattle virus (BTRV) were visualized in cells of the anther tissues of infected tomato plants. The BTRV appeared mostly as aggregates of parallel particles associated with mitochondria, though isolated aggregates and individual particles were seen in microspores and mature pollen grains. The BTRV particles could be seen in the cytoplasm of infected anther cells during the various stages of microsporogenesis from the stage of premeiotic cells to mature pollen grains. Virus distribution through meristems is the main mechanism that permits the BTRV to reach the pollen. Virus passage from somatic cells to the microspore-precursor cells while plasmodesmata are still functional may be complementary in case of early infection or the only way of access in late-infected plants. Both short and long particles could be seen in the cytoplasm of the vegetative and generative cells of the pollen. No virus particle was ever seen in the nuclei of infected cells, associated with the cellulose or callose walls, or on the outside wall of pollen grains. There was a small number of virus particles present in the microspore mother cells and microspores, and a large number of short- and long-particle aggregates in the mature pollen grains. These results indicate that virus increase occurs during pollen grain maturation and is not only the result of distribution. Microsporogenesis is comparable between infected and noninfected tissues. However, pollen grains from infected plants showed a lower germination than normal pollen.