dc.contributor.advisor |
Brown, J. |
en |
dc.contributor.advisor |
Dromgoogle, F. |
en |
dc.contributor.author |
Browse, John Anthony |
en |
dc.date.accessioned |
2007-08-28T11:33:35Z |
en |
dc.date.available |
2007-08-28T11:33:35Z |
en |
dc.date.issued |
1977 |
en |
dc.identifier |
THESIS 77-150 |
en |
dc.identifier.citation |
Thesis (PhD--Botany)--University of Auckland, 1977 |
en |
dc.identifier.uri |
http://hdl.handle.net/2292/1584 |
en |
dc.description |
Full text is available to authenticated members of The University of Auckland only. |
en |
dc.description.abstract |
The biochemistry and physiology of photosynthesis by Egeria densa Planch. were studied in plants collected from Meola Creek, Auckland. Time course and pulse chase 14C labeling experiments failed to confirm previous reports which suggested a major role of C-4 acids in carbon fixation. Under a wide range of total inorganic carbon (TIC) and pH conditions the distribution of label into PGA sugar phosphates and sucrose indicated that the Calvin cycle is the predominant pathway of carbon fixation. However at low levels of inorganic carbon supply malate synthesis by β-carboxylation accounted for up to 20% of the initial 14C fixed. The C-3 precursor for β-carboxylation may be derived from the glycollate pathway or from a six carbon intermediate involved in sucrose synthesis. The malate produced accumulates in an expanding pool in the light and is metabolised by reactions of the TCA cycle in the dark. The role of malate is discussed and it is concluded that this compound may be involved in balancing excess cation uptake by Egeria leaves in the light.
Infra red gas analysis was adapted to the study of aquatic plant photosynthesis and previous suggestions that high bicarbonate concentrations would preclude the use of open circuit IRGA techniques were shown to be largely unfounded. Experiments on the CO2 light and temperature responses of the photosynthesis in bicarbonate-free media (pH 4.5) showed that Egeria (1) has a high CO2 requirement for photosynthesis compared with terrestrial plants, (2) is a shade species, (3) shows a chilling response at low temperatures which may be the major factor limiting its ecological range. Application of the resistance concept demonstrates that despite a high carboxylation resistance, photosynthesis of free CO2 is largely limited by transfer across the boundary layer even when the thickness of this layer is minimised by high flow rates. Data from closed and open circuit IRGA experiments are used to demonstrate and quantify the contribution of bicarbonate to photosynthesis under a variety of TIC and pH conditions. Several mechanisms which might lead to the observed stimulation of photosynthesis in bicarbonate containing media are considered and it is concluded that bicarbonate ion is transported across the plasmalemma and is converted to CO2 within the cell. Labelling patterns during 14C tracer experiments and results of gas exchange studies demonstrated that photorespiration in Egeria is similar to the process described in terrestrial C3 plants. The importance of carbon loss by photorespiration is discussed with respect to the high oxygen and low inorganic carbon supply conditions experienced by Egeria in some natural situations.
A simple model of photosynthesis in Egeria is partially successful in predicting the changes in oxygen, pH and carbon species actually observed in the field and also indicates areas for future research. |
en |
dc.language.iso |
en |
en |
dc.publisher |
ResearchSpace@Auckland |
en |
dc.relation.ispartof |
PhD Thesis - University of Auckland |
en |
dc.relation.isreferencedby |
UoA9921812914002091 |
en |
dc.rights |
Restricted Item. Available to authenticated members of The University of Auckland. |
en |
dc.rights |
Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. |
en |
dc.rights.uri |
https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm |
en |
dc.title |
Photosynthesis in the aquatic macrophyte Egeria densa |
en |
dc.type |
Thesis |
en |
thesis.degree.discipline |
Botany |
en |
thesis.degree.grantor |
The University of Auckland |
en |
thesis.degree.level |
Doctoral |
en |
thesis.degree.name |
PhD |
en |
dc.rights.holder |
Copyright: The author |
en |
dc.identifier.wikidata |
Q111963740 |
|