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Title: An ultrastructural study of the embryogenesis and seed maturation of Capsella bursa-pastoris with an experimental approach to morphogenesis of the chloroplast
Author: Sharma, Vijay Kumar
ISNI:       0000 0001 3399 2745
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1977
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The literature relating to ultrastructure studies of angiosperm embryos up to seed maturity is reviewed. Ultrastructural changes in the cotyledon of the embryo of Capsella bursa-pastoris from the torpedo stage of embryogenesis to the mature seed are described. A revised classification of the developmental stages of the embryo is devised which recognises 11 stages, of which the final 8 stages are examined in the present study: the earlier 3 stages have already been studied by others. Particular reference is made to the development of the chloroplast. The chloroplasts increase in number, size, starch content and lamellar complexity as the embryo develops up to the mature-green stage, after which starch disappears abruptly. The deterioration and disruption of chloroplast lamellae begin after mature-green stage and are completed in the ivory-white and dry cotyledons. Some organelles (Golgi bodies, endoplasmic reticulum and nucleus) are recognizable in the dry cotyledon while other organelles are poorly defined or missing. The cotyledon develops storage tissue with numerous oil bodies and protein bodies in each cell. A single type of protein grain (aleurone grain) is formed within vacuoles. Oil bodies begin to appear from torpedo stage onward and reach a maximum in the ivory-white cotyledon. Ribosomes are dispersed freely in the cytoplasm. Literature on the effect of light and darkness in chloroplast morphogenesis in higher plants is reviewed. Development of the etioplast is studied in the embryos and leaves of whole plants subjected to darkness. Etioplasts of the embryo in the ovule contain large crystalline prolamellar body after 3 days dark treatment. Plastids of leaves subjected to darkness do not form prolamellar bodies but instead an extensive development of very variable, irregularly-shaped, stroma lamellae with characteristic ring- or cup-shaped or looped lamellae. The extensive development of the abnormal lamellar system with such peculiar arrangement is hitherto unknown in the plastids of normal higher plants. The transformation of the etioplast into chloroplast under illumination is investigated utilising embryo culture techniques as it was not practicable to observe such development in embryos from whole plants. The problem of excessive accumulation of starch in plastids was encountered but solved by reducing the sucrose concentration in the growth medium to 0.5% from the 2% used by others. A 1% sucrose concentration in the growth medium gives overall maximum growth of the embryo. After 4 days in darkness the etioplasts of cultured embryos contain well-formed crystalline and concentric prolamellar bodies. Treatment with 3 hours of continuous illumination with white light of low intensity completes the transformation of etioplast into chloroplast. Preliminary studies on the effect of light of different wavelengths on the etioplast transformation are also presented. Etioplasts in cultured embryos show typical protuberances of the jacket which are regarded as peripheral reticulum. The possibility of the formation of mitochondria from such protuberances is noted. Some novel structures developed in plastids are reported. Two types of tubules, distinct from the tubules forming prolarnellar bodies, are produced in the embryo. They appear as rows of small circular tubules and a group of long parallel tubules. The production of tubules, possibly the result of a reaction to the changed environmental conditions, are regarded as a sign of degeneration rather than a normal stage of development. Another novel structure reported in the etioplasts consists of a complex network of intermingled lamellae. It is concluded that the use of embryo culture technique in relation to experimental morphogenesis of organelles offers a promising field of study which will contribute also to our knowledge of embryo physiology and development.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Botany