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

Reproductive Structures and Seed Formation 41through the synergid, and lack of evidence that the sperm cytoplasm enters the eggor the central cell, are recorded during pollination and fertilization.The development of the endosperm may be nuclear, cellular, or helobial.Endosperm haustoria are found in several taxa of angiosperms. Available informationshows absence of plasmodesmatal connections in the embryo sac wall and thesurrounding tissue. Development of protuberances on the internal surface and themicroinvagination of plasmalemma, similar to those of transfer cells, are observed.This indicates that the transfer of nutrients from the maternal tissues to the newsporophyte including the endosperm takes place apoplastically.The development of the proembryo is similar in dicotyledons and monocotyledons.Differences develop during the organization of various parts of the embryo.The proembryo gets its nutrition through its basal suspensor cells, which developwall ingrowths. During the later stages nutrition is obtained from the endosperm.Changes take place in the nucellus, chalaza, and integument during seed development.Integuments undergo differentiation, absorption of cell layers, thickeningof cell walls, and deposition of pigmented material and crystals etc. One or morelayers of the seed coat develop characteristic thickenings, forming the main mechanicallayer. The seed coat is testal if the main mechanical layer is formed in the outerintegument and tegmic if it differentiates in the inner integument of a bitegmic ovule.Each type has several subtypes. The development and structure of the seed coat isfairly constant in a family.REFERENCESAgthe, C. 1951. Über die physiologische Herkunft des Pflanzen-nektars. Ber. Schweiz. Bot.Ges. 61: 240–277.Anderson, M.A., Lee, M., Heath, R.L., Nielson, K.J., Craik, D.J., Guest, D.J., and Clarke,A.E. 1996. Defence-related molecules in the pistil of Nicotiana alata. Plant Reproduction.14th International Congress of Sexual Plant Reproduction, Lorne (nearMelbourne, Australia), Abstract, p. 1.Arber, A. 1937. The interpretation of the flower: a study of some aspects of morphologicalthought. Biol. Rev. 12: 157–184.Atkinson, A.H., Heath, R.L., Simpson, R.J., Clarke, A.E., and Anderson, M.A. 1993. Proteinaseinhibitors in Nicotiana alata stigmas are derived from a precursor protein whichis processed into five homologous inhibitors. Plant Cell 5: 203–213.Baker, D.M. and Mebrahtu, T. 1990. Scanning electron microscopy examination of soybeanhilum development. Am. J. Bot. 68: 544–550.Bhatnagar, S.P. and Johri, B.M. 1972. Development of angiosperm seed. In Seed Biology.Kozlowski, T.T., Ed. Academic Press, New York, Vol. 1, pp. 77–149.Bocquet, G. 1959. The campylotropous ovule. Phytomorphology 9: 222–227.Boesewinkel, F.D. 1980. Development of ovule and testa of Linum usitatissimum. L. ActaBot. Neerl. 29: 17–32.Bor, J. and Bouman, F. 1974. Development of ovule and integuments in Euphorbia milli andCodiaeum variegatum. Phytomorphology 24: 280–296.Bouman, F. 1984. The Ovule. In Embryology of Angiosperms. Johri, B.M., Ed. Springer-Verlag, Berlin, pp. 123–157.