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

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Reproductive Structures and Seed Formation 23been observed in Capsella (Schulz and Jensen, 1972) and Helianthus (Newcomb,1973).The embryo sac wall lacks plasmodesmatal connections with the surroundingtissue (Orel and Shmaraev, 1987; Folsom and Cass, 1988; Johansson and Walles,1993). Its wall shows the formation of protuberances on the internal surface andmicroinvagination of plasmalemma (Figure 2.12A; see p. 30). These formations aresimilar to those of the transfer cells involved in short-distance transport of metabolites.2.7 FERTILIZATIONDouble fertilization is characteristic of angiosperms. The pollen tube is porogamous— entering the ovule through the micropyle (Figure 2.8A); chalazogamous —entering through the chalaza (Figure 2.8B); and, very rarely, mesogamous —penetrating laterally through integuments between the micropyle and chalaza. Inalmost all the economically important plants, the pollen tube enters the ovule throughthe micropyle and is porogamous. Under all the above conditions, the entry of thepollen tube into the embryo sac is at the micropylar end. The pollen tube entersthrough one of the synergids (Figure 2.8C), and the sperms are released in thecytoplasm of the synergid through a subterminal or terminal pore (Cass and Jensen,1970; Jensen, 1973). One sperm comes in contact with the egg plasma membraneand the other sperm come in contact with the plasma membrane of the central cell(Figure 2.8D, E). An opening in the fused plasma membranes of egg and spermallows the entry of the sperm nucleus into the egg. Similarly, the other sperm nucleusenters the central cell. There is no evidence of the entry of the pollen tube or spermcytoplasm in the egg or in the central cell.The sperm nucleus fuses with the egg nucleus. Three types of karyogamy —premitotic, postmitotic, and intermediate — are involved in their fusion (Gerassimova-Navashina,1960). The phenomenon is known as syngamy. The other malenucleus, which comes to lie close to the polar nuclei, or their fusion product, thesecondary nucleus, fuses with them to achieve triple fusion, forming the triploidprimary endosperm nucleus.2.8 SEED DEVELOPMENTPollination and fertilization provide the stimulus for the development of fruit andseed. The fertilized ovule undergoes changes in all parts during seed formation. Theovule enlarges, the zygote forms the embryo, and the primary endosperm cell withthe triploid nucleus forms the endosperm, which is required to provide nutrition tothe developing embryo. The nucellus, chalaza, and the integuments undergo varieddegrees of structural change. The development of seed is relatively constant in agroup. A general account of the development of the endosperm, embryo, and otherparts of the ovule is given here.
24 Histopathology of Seed-Borne InfectionsptoimiinuesptptABpnuecpmsyncwfasnusnssnptdpCptDEFIGURE 2.8 Course of pollen tube in ovule and embryo sac and the transfer of sperms. A,Ls ovule showing pollen tube entry through micropyle (porogamy). B, Ls ovule showingpollen tube traversing along the raphe bundle and entering nucellus through the chalazal endand the embryo sac at the micropylar end (chalazogamy). C to E, Entry of pollen tube intoone of the synergids (C), release of its contents into the synergid (D), and subsequentmovement of the two male gametes toward the egg and central cell. (Abbreviations: cw, cellwall; ec, egg cell; es, embryo sac; fa, filiform apparatus; ii, inner integument; m, micropyle;nu, nucellus; oi, outer integument; p, pore; pm, plasma membrane; pnu, polar nuclei; pt,pollen tube; ptd, pollen tube discharge; s, sperm; sn, sperm nuclei; snu, secondary nucleus;syn, synergid.) (C to E, From Jensen, W.A. 1973. Bioscience 23: 21–27. With permission.)
Page 2 and 3: Histopathology ofSeed-Borne Infecti
Page 4: PrefaceThe book deals with only one
Page 8 and 9: The AuthorsDalbir Singh, Ph.D., for
Page 10 and 11: ContentsChapter 1 Introduction ....
Page 12 and 13: 4.3.2 Routes for Infection from Ova
Page 14: 8.4 Survival in Seed ..............
Page 17 and 18: 2 Histopathology of Seed-Borne Infe
Page 19 and 20: 4 Histopathology of Seed-Borne Infe
Page 22 and 23: 2Reproductive Structuresand Seed Fo
Page 24 and 25: Reproductive Structures and Seed Fo
Page 26: Reproductive Structures and Seed Fo
Page 29 and 30: 14 Histopathology of Seed-Borne Inf
Page 37: 22 Histopathology of Seed-Borne Inf
Page 62 and 63: 3Structure of SeedsThe seed habit i
Page 64 and 65: Structure of Seeds 49(1971) of usin
Page 66 and 67: Structure of Seeds 51is found in as
Page 68 and 69: Structure of Seeds 53dry seed of Ly
Page 70 and 71: Structure of Seeds 553.3.2 SEED COA
Page 72 and 73: Structure of Seeds 57Endosperm: One
Page 74 and 75: Structure of Seeds 59scendembepsmuA
Page 76 and 77: Structure of Seeds 61Endosperm: Sca
Page 78 and 79: Structure of Seeds 63Chalaza simple
Page 80 and 81: Structure of Seeds 65stystypmerA Bc
Page 82 and 83: Structure of Seeds 67epsent endCADB
Page 84 and 85: Structure of Seeds 69perhscendembpe
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Structure of Seeds 73(Zea and Sorgh
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Structure of Seeds 75Baker, D.M. an
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Structure of Seeds 77Maheshwari Dev
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Structure of Seeds 79Vries, M.A. de
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82 Histopathology of Seed-Borne Inf
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TABLE 5.6Location of Mycelium of St
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7Seed Infection by VirusesViruses a
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Seed Infection by Viruses 201TABLE
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Seed Infection by Viruses 205Unlike
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Seed Infection by Viruses 2073. The
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Seed Infection by Viruses 209Wilcox
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Seed Infection by Viruses 213floret
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Seed Infection by Viruses 215ptowvv
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Seed Infection by Viruses 2177.4.2
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Seed Infection by Viruses 219seed(s
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Seed Infection by Viruses 221AMV fo
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Seed Infection by Viruses 223REFERE
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Seed Infection by Viruses 225Hunter
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Seed Infection by Viruses 227Wolf,
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