Histopathology of Seed-Borne Infections - Applied Research Center ...

210 Histopathology of Seed-Borne InfectionsovcwcwovABCDfummEFFIGURE 7.2 Distribution of pea seed-borne mosaic virus (PSbMV) RNA in the ovary tissuebefore and after fertilization (dark areas represent virus RNA concentration also marked byarrow). A, B, Ls through unfertilized ovaries of cultivars Progreta and Vedette, respectively,showing viral RNA restricted mostly to the carpel tissue. C, D, Ls fertilized ovaries showingthe ingress of the virus into the ovule along the vascular tissue (arrow). E, F, magnified viewsof ovules from C, D to show the ingress of the virus. (Abbreviations: cw, carpel wall; fu,funiculus; m, micropyle; ov, ovule.) (From Wang, D. and Maule, A.J. 1994. Plant Cell 6:777–787. With permission.)strain (MI-1) in a susceptible cultivar Atlas. The infection reaches the primordia forfertile appendages — stamen and pistil — quite early. In the anther, cells of walllayers, connective, anther sac-male archesporium, and its derivatives (i.e., microsporemother cells, dyads, and microspores in tetrads), pollen grains contain virus particlesin the cytoplasm individually, in clusters, and attached to the microtubules. The virusoccurs in vegetative cells and in sperm cells (Figure 7.4A to C), and in the latter inthe cytoplasm as well as the nucleus (Carroll, 1974; Carroll and Mayhew, 1976a).The pollen grains are viable and after pollination, they germinate, and pollen tubesenter the stigma and style, ovule, and embryo sac, and discharge their contents inthe cytoplasm of the degenerating synergid (Figure 7.5A to D). BSMV particlesoccur in pollen tubes at all stages and also in the contents discharged in the embryosac (Brlansky, Carroll, and Zaske, 1986).In the ovule, the BSMV particles have been observed in the integument, nucellus,female archesporium (Figure 7.6A, B), megaspore mother cell, megaspores, two-,four-, and eight-nucleate embryo sacs, and in cells (synergids, egg, and antipodalcells) of the organized embryo sac (Figure 7.6C to E) (Carroll and Mayhew, 1976b;Mayhew and Carroll, 1974). After fertilization, clusters of BSMV particles are seen