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Table of contents
Chapter 1: General introduction
1. 1. Marine ecosystems, phytoplankton and photosynthesis
1. 1. 1. Most of the genetic diversity in the Ocean is known
1. 1. 2. Phytoplankton plays a crucial role in fluxes of matter and energy in the ocean
1. 1. 3. Origin and taxonomic diversity of phytoplankton
1. 2. Reactions and mechanisms involved in eukaryotic photosynthesis
1. 2. 1. Different types of photosynthesis
1. 2. 2. The chloroplast: an organelle hosting photosynthesis
1. 2. 3. The Calvin-Benson-Bassham cycle synthesizes organic carbon from CO2
1. 2. 4. The photosynthetic electron transfer chain uses light energy to supply the CBB cycle
1. 2. 5. From light absorption to energy storage
1. 2. 6. Monitoring photosynthesis with chlorophyll fluorescence
1. 3. Regulation of the photosynthetic process and acclimation to changing environments
1. 3. 1. Light stress and photo-inhibition
1. 3. 2. Protecting photosystem I and II from light stress
1. 3. 3. Photosynthetic alternative pathways
1. 3. 4. CEF, a crucial regulative pathway remaining mysterious
1. 4. Thesis outline
1. 5. Bibliography
2 Exploring the diversity of cyclic electron flow around photosystem I in microalgae species
Chapter 2: Probing PSI activity
2.1. How to probe photosystem I with absorption spectroscopy?
2.1.1. Some reminders about photosystem I
2.1.2. Measuring P700 redox state to investigate PSI activity
2.1.3. Electrochromic Shift: an internal voltmeter
2.2. Article: Critical reappraisal of methods to measure photosystem I activity
2.3. Discussion
2.3.1. The P700 pulse method underestimates Y(I) because of reduction of PSI acceptors during the multiple turnover pulse
2.3.2. Technical considerations regarding P700 measurements
2.3.3. Generalization to the case of an active photosystem II
2.3.4. Revisiting the literature based on the P700 pulse method
2.3.5. Partial conclusions and transition
2.4. Bibliography
Chapter 3: Diversity of cyclic electron flow in microalgae
3.1 Introduction: CEF, a still mysterious alternative pathway
3.1.1. Role of CEF in ATP/NADPH adjustment and photo-protection
3.1.2. Regulation of CEF rate
3.1.3. Measuring CEF is a methodological challenge
3.1.4. Chapter outlines
3.2 Material and methods
3.2.1 Strains, growth and sampling
3.2.2 Chemicals
3.2.3 In vivo spectroscopy
3.2.4 ECS spectra and linearity with electric field
3.2.5 Absorption cross section assessment
3.3 Results (I): Exploring CEF diversity
3.3.1 DCMU titration reveals CEF behavior
3.3.2 Which observables?
3.3.3 CEF is not essential to photosynthesis in the dinoflagellate Amphidinium carterae
3.3.4 CEF is independent on LEF photosynthesis in the dinoflagellate Symbiodinium sp.
3.3.5 Chlamydomonas reinhardtii displays a CEF which is dependent on LEF
3.3.6 Partial conclusion on CEF diversity
3.4 Results (II): Evaluating CEF and LEF absolute rates as a function of light irradiance in the green alga Chlamydomonas reinhardtii
3.4.1 ECS-based estimations of the PSI and PSII absorption cross sections
3.4.2 Validation of the method for measurement of absorption cross sections
3.4.3 Evaluating CEF absolute rates from ETR(total) and ETR(II)
3.4.4 Calculations of the ATP/NADPH ratio produced by the photosynthetic chain
3.5 Discussion and future perspectives
3.5.1 A simple and robust protocol to investigate CEF diversity highlights three different behaviors
3.5.2 Limitations of the DCMU titration method
3.5.3 Despite a complex relationship, CEF and LEF remain proportional at all light intensities in Chlamydomonas reinhardtii
3.6 Bibliography
Chapter 4: Photosynthetic physiology of the coccolithophore Emiliania huxleyi Major environmental determinants and signature of viral infection in the field
4.1 Introduction
4.2 Material and methods
4.2.1 Mesocosm setup, treatments and sampling
4.2.2 Flow cytometry/ qPCR
4.2.3 Measurement of environmental (abiotic) parameters
4.2.4 Photophysiology by Fast Induction and Relaxation fluorometry (FIRe)
4.2.5 Statistical analyses
4 Exploring the diversity of cyclic electron flow around photosystem I in microalgae species
4.3 Results
4.3.1 A two phases phytoplankton bloom occured
4.3.2 Photosynthetic physiology
4.3.3 Fluorescence signals were mainly due to Emiliania huxleyi from day 9 to 24th of the experiment
4.3.4 Evolution of environmental parameters during the experiment
4.3.5 Environmental determinants of E. huxleyi photosynthesis
4.3.6 A photosynthetic signature of viral infection?
4.4 Conclusion and discussion
4.5 Bibliography
Chapter 5: General discussion
5. 1. 1. The importance of cross validations of methods
5. 1. 2. Using the flash-induced ECS to estimate the photochemical rate: a good choice?
5. 1. 3. Studying CEF and its abiotic and biotic determinants in the field: an accessible project?
5. 2. Roles of CEF and mechanisms of the regulation of the CEF and LEF
5. 2. 1. ATP:NADPH ratio equilibration
5. 2. 2. A role of CEF when PSII is inhibited?
5. 2. 3. CEF and LEF regulation
5. 3. Three years were too short for…
5. 3. 1. Revisiting literature using P700 method
5. 3. 2. Exploring cyclic electron flow using our methods
5. 3. 3. Harness all data collected in the field
5. 4. Bibliography
Appendix
