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

220 Histopathology of Seed-Borne InfectionsmmABFIGURE 7.9 (Color figure follows p. 146.) Diagrammatic analysis of the distribution of peaseed-borne mosaic virus (PSbMV) in longitudinal section through immature pea seeds byimmunocytochemistry using a monoclonal antibody to PSbMV coat protein in cultivar Vedettepermissive for seed transmission and cultivar Progreta with nonpermissive interaction. A,Diagrammatic Ls of immature seed of cultivar Vedette showing widespread accumulation ofthe virus in testa tissues reaching near the micropyle providing point of contact between thetesta tissues and the embryonic suspensor through which the virus enters embryo. B, Samefor cultivar Progreta showing entry of virus through the vascular supply of the seed but thevirus is unable to invade the adjacent testa tissues — a nonpermissive interaction. (Abbreviation:m, micropyle.) (From Maule, A.J. and Wang, D. 1996. Trends Microbiol. 4: 153–158.With permission.)These have been widely observed in cells of vegetative parts by light microscopyand in recent years by electron microscopy, and the data are summarized by Mathews(1991) and Shukla, Ward, and Brunt (1994). The effects of virus infection occur onthe nuclei, mitochondria, chloroplasts, and cell wall and are also observed as formationsof cytoplasmic inclusions (cylindrical, crystalline, and pinwheel-shaped),and formations of nuclear inclusions (crystalline, amorphous, and tubular). Theinformation on virus-induced inclusions in seed tissues is limited, and the effectson the nuclei and cell organelles have not been reported. LMV-induced cylindricalinclusions have been found throughout the ovular tissues, and are particularly abundantin the integumentary tapetum, residual integumentary cells, ovary wall (Hunterand Bowyer, 1994), in the embryo, endosperm, and pericarp (Hunter and Bowyer,1993). Cytoplasmic pinwheel inclusions with the most characteristic feature of acentral tubule, from which curved arms radiate (Figure 7.7D), are observed in theintegumentary tapetum and embryonic tissues, but not in the cells of the pericarp.Lamellar structures with LMV particles in association are seen in integumentarytapetal cells, but Hunter and Bowyer (1994) consider them of unknown origin.