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Title: Photoinhibition of primary production in marine phytoplankton : modelling photon damage and non-photochemical quenching
Author: Marshall, H. L.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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Photoinhibition in three species of prymnesiophyte algae (Isochrysis galbana, Phaeocystis globosa and Emiliania huxleyi) was investigated using inhibitors to isolate various components. Results suggested that the three species show the same general responses, but timing and magnitude varied. I.galbana was the least susceptible to high light stress and showed a faster and greater non-photochemical quenching response than the other two species. This may be due to genetic adaptation, however characterisation of many more species is required before it becomes clear how photoinhibition responses vary in situ. A mathematical model was developed that simulates photon damage of photosystem II and subsequent effects on the initial slope of the photosynthesis/irradiance curve. Species specific differences in photoinhibition are proposed to be due to differences in pigment content and photoprotection. This was supported by the results presented, in that for each of the three species, the decline in the ratio of variable:maximum fluorescence normalised to Chlorophyll a for a given number of photons, is the same for a give species regardless of exposure irradiance. An additional model was constructed to simulate 3-step xanthophyll cycling (violaxanthin, antheraxanthin & zeaxanthin) in higher plants and chlorophyte algae. Both models were incorporated within existing photoacclimation models. The resultant model can simulate dynamic photoacclimation and photoinhibition under both nutrient replete and limiting conditions, and compares well with independent published experimental results. Experimental investigations into the 2-step xanthophyll cycle seen in prymnesiophyte algae (diadinoxanthin & diatoxanthin) presented here suggested that the relationship between non-photochemical quenching and the epoxidation state of the cycle was not as simple as the relationship seen in higher plants. Further research is required to clarify the relationship between non-photochemical quenching and this 2-step cycle, and the part of non-photochemical quenching that occurs in the presence of inhibitors of the de-epoxidation step of this cycle (DpH dependant quenching).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available