Particles of Rice Gall Dwarf Virus in Thin Sections of Diseased Rice Plants and Insect Vector Cells

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Abstract
Summary Rice gall dwarf virus (RGDV) was studied in infected rice plants and in its principal insect vector, the green leafhopper Nephotettix nigropictus, by electron microscopy. In plants, virions were restricted to the cytoplasm and vacuoles of phloem-related cells and of gall cells generated from the phloem. In the insects, virions occurred in the cytoplasm of many different kinds of cells including those of the salivary gland, the gut, the fat body, muscles and nerves. Virions in both plant and insect cells had dense cores 40 to 50 nm in diameter which were surrounded by a less dense region; the total diameter was 60 to 70 nm. Viroplasms, crystals and tubules were observed in cells both of plants and insects. Although virions often occupied most of infected plant cells, they occurred only in restricted areas of insect cells. The restriction of virions to phloemrelated cells in infected plants probably explains why yields of purified RGDV are usually about 1/30 of those of rice dwarf virus, which invades many types of cell. About 3% of the virus particles seen in thin sections of infected plants appeared to be empty. Empty particles were purified from infected rice plants and were found to lack nucleic acid and much of the 56000 mol. wt. protein present in intact particles.