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

Seed Infection by Viruses 219seed(seed coat +embryo +)embryo (+)early cotyledonarystageradicle end (+)suspensor (+)embryo properremainder (−)globularcordatestageseedling(+)suspensor (+)embryo proper (−)infected plant(+)sepals (+)petals (+)epidermis(+)antherpollen grains (−)flowerovary(vascular zone +)other parts(−)ovule(before fertilization)funiculus(+)body(−)embryo sac cells(−)pollination and fertilizationyoung proembryoendosperm(+)seed coatvascular bundlein raphe &integument (+)fertilized ovuleprimaryendosperm cell(−)zygote(−)embryo sacFIGURE 7.8 Schematic representation of infection cycle of PSbMV in a high seed transmittingcultivar in pea. (+) = presence of virus. (–) = absence of virus. (Based on the publicationsof Wang and Maule.)direct embryo invasion in pea, it varies with virus–host cultivar combination. Theembryonic suspensor is the main conduit for virus invasion of the embryo proper.The development of wall ingrowths in cells of the suspensor adjacent to the embryosac boundary and the occurrence of plasmodesmata between the cells of the suspensorand those of the suspensor and endosperm provide support to this pathway(Johansson and Walles, 1993).There are many other viruses reported in the embryo (Table 7.4). It may bepointed out that most viruses found in the embryo are also located in the endospermand seed coat and pericarp as seen for BSMV in barley, LMV in lettuce, and PSbMVin pea.7.5 CYTOPATHOLOGICAL EFFECTSViruses are known to induce histological as well as cytological changes includingformation of in vivo cytoplasmic and nuclear inclusions in cells of infected plants.