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Title: Studies on secretion and absorption in Dionaea muscipula Ellis
Author: Robins, Richard J.
ISNI:       0000 0001 3527 0180
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1978
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The ultrastructure and physiology of the secretory glands of Dionaea muscipula Ellis (The Venus's Flytrap) have been examined in order to investigate the mechanism of obtaining nutrients practised by this plant. The dynamic changes in the ultrastructure following stimulation have been examined. Particularly prominent features are a decrease in the size of the main cell vacuole and an increase in smaller vacuoles. Important changes are also observed in the distribution of ribosomes within the secretory cells. By the use of high resolution histochemical, cytochemical, and autoradiographic methods, it is shown that the secretory hydrolases are probably stored in a sub-compartment of the vacuole, the smooth endoplasmic reticulum and the cell walls. It is shown by quantification of the cell and by autoradiography that the dictyosomes do not appear to be involved in the discharge of secretion, but rather that this probably occurs both by direct fusion of the endoplasmic reticulum with the plasmalemma and by the migration of vesicles derived from the endoplasmic reticulum directly to the cell periphery. Evidence is presented to show that, in addition to being released from a site of storage, some of the protein discharged is synthesized de novo during the cycle. This is suggested by the observed formation of numerous polysomes associated with the endoplasmic reticulum in the secretory cells and confirmed by radiolabelling techniques. A preliminary analysis of the enzymology of the secretion is presented and it is tentatively suggested that there are several peptide hydrolase activities present, possibly including a serine proteinase and a carboxypeptidase. It is shown that the secretion can hydrolyse chitin and has peroxidase activity. By following the absorption of chloride ions, it is shown that the plasmodesmata are important in the uptake of these ions. The overall architecture of the gland is considered in relation to the possible pathway of absorption of digestive products and it is suggested that the plasmo-desmata are probably the primary route for the movement of nutrients into the glands. A model is put forward, based on these observations, for the way in which the gland conducts a bi-directional flow of material. It is hypothesized that, while absorption takes place via the symplast, secretory proteins are discharged directly into the apoplast and flushed from there by hydrostatic pressure generated by the inner secretory cells. Suggestions are made for how this might be achieved.
Supervisor: Juniper, Barrie Edward Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Plant cells and tissues ; Plant exudates ; Plant physiology ; Absorption (Physiology) ; Venus's flytrap