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Title: Protein synthesis in etioplasts and developing chloroplasts
Author: Siddell, Stuart G.
ISNI:       0000 0001 3408 6242
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1976
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1. The aim of this work was to study the etioplasts and developing chloroplasts. The conclusions reached are interpreted in the context of plastid autonomy and biogenesis. 2. I have shown that isolated etioplasts and developing chloroplasts use added ATP as an energy source for amino acid incorporation into protein. Developing chloroplasts isolated from leaves after a minimum of 3 hours greening in continuous white light can also use light as an energy source for protein synthesis. 3. The relationship between ATP and light as an energy source for in vitro plastid protein synthesis has been studied in plastids isolated during greening. 4. The characteristics of amino acid incorporation in rapidly isolated etioplast preparations exclude the possibility that incorporation occurs on cytoplasmic ribosomes, in whole cells, nuclear bacteria and are consistent with the known characteristics of in vitro plastid protein synthesis. 5. It has been shown that less than 3% of the amino acid incorporation into protein in etiolate suspensions is associated with mitochondria which contaminate the preparations. 6. The conditions for optimum incorporation of amino acids into protein were order to facilitate the identification of the polypeptides synthesized. 7. The products of in vitro protein synthesis were analysed by electrophoretic separation on SDS urea polyacrylamide gels. 8. Using ATP as the energy source and either L-(35S) methionine, L-(3H) leucine or L-(3H) phenylalanine, as the protein precursor it has been shown that etioplasts synthesize seven major polypeptides. 9. These polypeptides electrophorese coincidentally with the products of protein synthesis in isolated chloroplasts. 10. As in chloroplasts of these polypeptides is present in a 150,000g etioplast supernatant fraction. This product has been identified as the large subunit of Fraction I protein. Identity was established by comparing the tryptic and chymotryptic peptide map of the in vitro etioplast product labelled with L-(35 S) methionine with the tryptic and chymotryplic peptide map of authentic large subunit of Fraction I protein labelled with L-(35S) methionine in vivo. 11. The same gel pattern of seven polypeptidesis seen when plastids isolated from greening leaves are incubated with either added ATP or light as the energy source. The products of in vitro protein synthesis in developing chloroplasts also co-electrophorese with those synthesized in isolated chloroplasts. 12. The rates of synthesis of particular polypeptides are different in plastids isolated at different stages of the etioplast to chloroplast transition. 13. The results support the idea that plastid ribosomes synthesize only a small number of proteins and that the number and molecular weight of these proteins does not alter during the formation of chloroplasts from etioplasts. 14. The results are discussed in the context of plastid autonomy and biogenesis. The use of the plastid as a developmental system for studying the controls exerted upon the synthesis of particular polypeptides during differentiation is considered. Possible areas of research which might be undertaken as a result of the work described are outlined.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QK Botany