Fine Structures and Developmental Process of Tubules Induced by Mulberry Ringspot Virus and Satsuma Dwarf Virus Infections

Abstract

Cowpea leaves infected with mulberry ringspot virus (MRSV) or satsuma dwarf virus (SDV) at different growth stages were examined under an electron microscope. In the MRSV infected leaf primordia single rows of virus particles were found in the plasmodesmata of the cells near the apical points. The rows of particles were thrusted into the cytoplasm at one side of the plasmodesmata. In leaves 2-5mm, the thrusted rows were bounded with invaginated plasmalemma. Tubules thus developed grew longer with the growth of leaf, up to 5μm in length, and cell walls were protruded deeply into the vacant spaces caused by invagination of plasmalemma. In SDV infected cowpea plants, rows of virus particles in the plasmodesmata appeared for the first time in leaves 1mm in length and tubules developed in the similar process as observed in the MRSV infected cells. Cytoplasmic inclusions consisting of tangled endoplasmic reticulum occurred in the cowpea leaf cells infected with MRSV or SDV. Similar tubules and inclusions occurred in the leaf cells of sesame, kidney bean, petunia, and Nicotiana clevelandii plants infected with SDV. The tubules were found also in the spaces between the plasmalemma and cell wall in the cells of N. clevelandii and kidney beans. The walls of these tubules were joined to plasmalemma. The tubules containing single rows of virus particles were observed in dip preparations of infected leaves.