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Title: Symbiosis in Convoluta roscoffensis
Author: Douglas, Angela Elizabeth
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1981
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1. Culture methods for the maintenance of symbiotic adult and juvenile Convoluta roscoffensis have been developed. The growth of adults but not juveniles is dependent on nitrogen enrichment of the medium. 2. Electron microscopic studies suggest that the algal symbionts in adult Convoluta are intracellular. 3. Structural studies of the gametes and early development of Convoluta are described. 4. Relevant aspects of the biology of the natural Convoluta symbiont, Platymonas convolutae, and a range of related algae have been studied. The growth of all Platymonas and Tetraselmis species tested except P.convolutae is stimulated by 0.1 M glucose. Glucose supports the growth of T.tetrathele, T.suecica and P.subcordiformis in darkness. P.convolutae and T.tetrathele have two uptake systems for uric acid, which conform to Michaelis-Menten kinetics; a high affinity system, operating in the concentration range 0.2-4.5 pM, and a low affinity system, operating at higher concentrations of uric acid. Uric acid uptake by P.convolutae is abolished by uncouplers of phosphorylation. Exogenous uric acid is accumulated in cells of Platymonas and Tetraselmis species up to internal concentrations of 0.3 M. P. convolutae metabolises (2-14C) uric acid to (14 C) carbon dioxide in the dark. 5. Aposymbiotic juvenile and symbiotic adult Convoluta, under standard culture conditions, contain solid uric acid. The uric acid content of juveniles declines on infection with P.convolutae and related species. Uric acid is utilised in the adult symbiosis, particularly under conditions of nitrogen demand. 6. Motile cells of P.convolutae and related species and Chlamydomonas coccoides aggregate around Convoluta eggs. These algae 'settle' on the eggs, by an interaction initiated by contact between the algal flagella and egg capsule surface. Living and killed algae are trapped by the capsules. No evidence that P.convolutae cells exhibit chemotaxis towards Convoluta eggs has been obtained. 7. Juvenile Convoluta ingest species of Platymonas and Tetraselmis, Prasinocladus marinus and Chlamydomonas coccoides but no other algae tested. Ingestion of P.convolutae is not affected by pretreatment of the cells with lectins or proteolytic enzymes, but is reduced if the algae are killed. 8. Cells of C.coccoidea, but not P.convolutae and related species, are disrupted in juvenile Convoluta. 9. Juvenile Convoluta form a viable symbiosis with P.convolutae, Pr.marinus, T.tetrathele and T.verrucosa under laboratory conditions. The structural changes of P.convolutae and T.verrucosa during the development of the symbiosis are described. 10. It is proposed that Convoluta discriminate against species unrelated to P.convolutae on initial contact and in the digestive region of the host. Evidence for a recognition mechanism discriminating between P.convolutae and related species is discussed. The nature of the recognition mechanism(s) has not been established.
Supervisor: Not available Sponsor: Science Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Platyhelminthes ; Symbiosis