A functional analysis of cell cycle events in developing and germinating tomato seeds

R.D. de Castro

Research output: Thesisinternal PhD, WU

Abstract

<p>Seeds are complex biological structures and the primary dispersal units of higher plants. They consist of nutrient reserve storage tissue(s), an embryo and encapsulating structures designated for protection and that may also regulate germination. Seeds have developed mechanisms of withstanding desiccation without losing the ability of immediate reactivation of embryo growth upon rehydration.</p><p>The arrest and reactivation of cell cycle related events appear to be intimately linked to the arrest of growth during seed development and reactivation of growth during germination. In this thesis, DNA synthesis,β-tubulin accumulation and appearance of microtubular cytoskeleton are studied in relation to morphological and physiological events that are involved in seed development and germination. Biochemical techniques are used to study the relation between DNA replication andβ-tubulin accumulation in embryonic cells of germinating seeds (Chapters 2 and 3). Then, immunocytochemical techniques are applied for the detection and visualisation of DNA synthesis activity and appearance of microtubular cytoskeleton in seed tissues during development and in embryos during germination (Chapters 4, 5 and 6).</p><p>The results obtained in this study show a general pattern of tomato seed development and germination based on the quantitation and distribution of nuclear DNA synthesis activity,β-tubulin accumulation and microtubular cytoskeleton appearance in cells of the seed tissues. The pattern in embryos during seed germination appeared as a "mirror image"of that during development (Chapters 4 and 5). Cell cycle activities are intense during early stages of seed development and then arrest as seeds become mature. Embryonic DNA synthesis activity, together with the presence of mitotic microtubular cytoskeleton arrays and cell divisions define the period of embryo histodifferentiation. Therafter, the presence of cortical microtubular cytoskeleton and absence of DNA synthesis acitvity defines the phase of embryo growth and completion of morphogenesis. Finally, the microtubular cytoskeleton is degraded as seeds become quiescent, defining the maturation phase. The roles of GA and ABA in seed development are evaluated in the differing developmental patterns observed for the GA-deficient ( <em>gib1</em> ) and ABA-deficient ( <em>sit <sup>w</em></SUP>) mutants. Upon imbibition in water, the cell cycle is reactivated and becomes intense as germination is completed. Initially, the cortical microtubular cytoskeleton appears and DNA synthesis is initiated in meristematic cells of embryonic radicle tip region. Thereafter, replicated nuclear DNA is detected together with mitotic microtubular cytoskeleton arrays and cell divisions, prior to radicle protrusion through the seed coat. Both primary and secondary dormancy are characterised by a very low cell cycle activity. The depth of dormancy appears to be related to the progression of the cell cycle prior to the induction of dormancy (Chapter 6).</p><p>Finally, in the form of a descriptive model, it is proposed to modify the current notion of the different phases in tomato seed development and germination.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Karssen, C.M., Promotor
  • Hilhorst, Henk, Promotor
  • Bino, R.J., Promotor, External person
Award date11 Sep 1998
Place of PublicationS.l.
Print ISBNs9789054859307
Publication statusPublished - 1998

Keywords

  • germination
  • seed germination
  • seed dormancy
  • seeds
  • seed testing
  • characteristics
  • solanum lycopersicum
  • tomatoes

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