Fine structural studies on differentiation and dedifferentiation in the higher plant

Fasseas, Constantinos (1980) Fine structural studies on differentiation and dedifferentiation in the higher plant. PhD thesis, University of Glasgow.

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The storage cells in the cotyledons of air-dried Phaseolus vulgaris seeds contain large quantities of polysaccharides, protein and to a lesser extent, lipids. A single multilobed nucleus occurs in the centre of each storage cell surrounded by large starch grains, small plastids and mitochondria whilst the cytoplasm occupies the narrow channels between the various organelles. The cell walls are composed of two layers, the outer, cellulosic, and inner, non-cellulosic, and the latter serves as a polysaccharide store. After hydration for 24 hours the storage cells respond to in vitro culturing, on solid medium (Murashige and Skoog, 1962) containing 2,4-D, kinetin and coconut milk, by producing a callus tissue which, when routinely subcultured, continues to grow for a potentially indefinite period. No organogenesis was observed in the callus cultures during the one year of cultivation. The callus appears on the adarial side of the cotyledon (which is in contact with the medium) and, initially, mainly developes from the storage cells in the vicinity of the adaxial provascular strands and progressively spreads towards the abaxial surface. The nuclear divisions observed are mainly amitotic with mitoses apparently being confined to storage cells which have already undergone nuclear fragmentation. Free-wall formation occurs frequently in automatically dividing cells and plays an active role in nuclear fragmentation. Large labyrinthine wall bodies are abundant in the dedifferentiating storage cells, apparently free in the cytoplasm or more often forming on the cell walls. Wall bodies also occur, along with freely-forming walls, in the established callus. A comparison is also made between in vivo and in vitro development of the cotyledon; vitro food digestion proceeds slowly and it is faster on the adaxial side, in comparison to relatively fast food digestion when vivo which occurs more uniformly in the storage tissue. Neither-cell division for organelle replication occur during germination The air-dried Linum usitatissimum hypocotyl serves as food store (along with the rest of the embryo) during seed dormancy, with the main food stores being lipid, protein and polysaccharides; during germination protein bodies are digested and give rise to vacuoles. The hypocotyl reaches its full height at about Day 10; by that time stomata are fully differentiated and in addition to the normal epidermal cells and guard cells, "swollen" cells occur at various sites in the epidermis; all .epidermal cells contain a spindle-shaped nuclear inclusion. Decapitation of the Day 10 hypocotyl results in the appearance of 5-20 novo developed adventitious buds which become macroscopically visible at the upper end of this organ by about Day 10. The majority become dormant but one bud eventually becomes dominant and grows into a replacement shoot. The initiation of a bud is characterised by several transverse divisions in the axially elongated, normal- type epidermal cell, followed by radial and tangential longitudinal ones. The cortical cells, in the case of a non-dormant bud, appear to dedifferentiate more-or-less contemporaneously with the epidermal cells and a provascular connection becomes established between the bud and the axial vascular tissue of the hypocotyl. In the dormant bud this connection appears to occur later when leaf primordia are already visible and only some discontinuous tracheary elements differentiate in contrast to continuous strands in the non-dormant bud. Dedifferentiation of epidermal and cortical cells is apparently accompanied by the appearence of some highly irregular chloroplast profiles indicating some kind of chloroplast replication. After decapitation the hypocotyl becomes greener, its top swells, the cell walls of cortical cells become thicker, cortical chloroplasts develop massive starch grains and transfer cells appear in the vascular tissue connecting the adventitious bud with the axial vascular tissue as well as in the latter itself.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: B G Bowes
Keywords: Plant sciences
Date of Award: 1980
Depositing User: Enlighten Team
Unique ID: glathesis:1980-72881
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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