Seed development and carbohydrates

P.E. Wittich

Research output: Thesisinternal PhD, WU

Abstract

<p>Seeds assure the plant the onset of a next generation and a way of dispersal. They consist of endosperm and an embryo (originating from gametophytic tissue), enveloped by a seed coat (sporophytic tissue). Plants generate different types of seeds. For instance, the endosperm may either be consumed by the embryo during seed development or retained for use by the embryo during germination. Differences in timing of endosperm digestion can be illustrated with broad bean ( <em>Vicia faba</em> ) and <em>Gasteria verrucosa</em> . Broad bean forms seeds in which the endosperm has been consumed by the fully developed embryo, while the embryo of <em>Gasteria</em> is less developed and surrounded by a large amount of endosperm for use during germination.</p><p>An important factor in seed development is the distribution, storage, and utilization of carbohydrates, since carbohydrates are a major source of energy for cell growth. In this thesis the carbohydrate distribution is studied in developing ovules and seeds of maize ( <em>Zea mays</em> ) and <em>Gasteria</em> , by identifying the cells and tissues in which sucrose is degraded. Sucrose is the main carbohydrate supplied by these plants in the developing seeds. The sucrose degrading activity of the enzymes sucrose synthase and invertase indicates the destination of the sucrose transport (Chapters 9 and 10). Immunocytochemical and histochemical techniques are used for the localization of these enzymes <em>in situ</em> .</p><p>The results obtained in this study on maize (Chapter 2 and 3) and <em>Gasteria</em> seed development (Chapters 4 and 5) show a general pattern of carbohydrate transport. First, the greatest amount of carbohydrates is applied for the development of the seed coat and nucellus (sporophytic tissues). An example of such a carbohydrate consuming process is the deposition of phytomelan in the seed coat of <em>Gasteria</em> . Phytomelan is a black cell wall component and chemically very inert. Histochemical and electron microscopy observations (Chapters 6 and 7) show that callose forms a mould for the deposition of phytomelan. The breakdown products of callose (glucose monomers and polymers) seem to be used for the synthesis of the phytomelan. Chemical analysis reveals that phytomelan is a complex polyphenolic polymer, and not a melanin (Chapter 8). Second, carbohydrate transport to the sporophytic tissues is followed by transport of most carbohydrates into the endosperm. These carbohydrates will be used for endosperm growth and for storage. Finally the main carbohydrate flow will go to the embryo. The pattern of carbohydrate usage observed in maize and <em>Gasteria</em> was used to generate a general model for angiosperm seed development (Chapter 10). The model explains differences between seeds by relating carbohydrate distribution during seed development to the timing of seed dispersal.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Willemse, M.T.M., Promotor
  • van Lammeren, A.A.M., Promotor, External person
  • Keijzer, C.J., Promotor, External person
Award date19 May 1998
Place of PublicationWageningen
Publisher
Print ISBNs9789054858553
Publication statusPublished - 1998

Keywords

  • seed set
  • seeds
  • formation
  • plant physiology
  • plant development
  • fruits
  • ripening
  • plants
  • embryology
  • metabolism
  • plant nutrition
  • assimilation
  • carbohydrates
  • vicia faba
  • gasteria verrucosa
  • organic chemistry

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