Prying into the green black-box.
Agu Laisk1,2
1Institute of Technology, University of Tartu, W. Ostwaldi 1, 51011, Tartu, Estonia. agu.laisk@ut.ee.
Photosynthesis Research
|September 16, 2022
Summary
This study reveals key insights into leaf photosynthesis, including Rubisco enzyme kinetics and electron transport pathways. Novel findings challenge existing models of photosystem II connectivity and highlight feedback regulation in ATP synthesis.
Area of Science:
- Plant Physiology
- Photosynthesis Research
- Biophysical Chemistry
Background:
- Decades of research in photosynthesis have yielded sophisticated understanding of light-dependent reactions.
- Previous models of enzyme kinetics and electron transport pathways require refinement based on in vivo measurements.
- Understanding the regulation of ATP synthesis is crucial for comprehending overall photosynthetic efficiency.
Purpose of the Study:
- To summarize life-long efforts in photosynthesis research from the Tartu group.
- To investigate the in vivo kinetics of Rubisco and electron flow dynamics.
- To elucidate the mechanisms behind chlorophyll fluorescence induction and ATP synthesis regulation.
Main Methods:
- Development of multifunctional, fast-response, black-box type instruments for intact leaf measurements.
- Kinetical analysis of Rubisco activity, measuring substrate and product competition.
- Precise quantification of absorbed photons, transmittance changes, and electron flow rates through Photosystem I (PSI) and Photosystem II (PSII) components.
Main Results:
- In vivo Rubisco kinetics differ from in vitro, showing linearization due to substrate-product competition; Rubisco Activase activates only a fraction of Rubisco.
- Competition exists between cyclic and linear electron flow pathways; electron flow rates through cytochrome b6f, plastocyanin, and PSI were measured.
- Sigmoidal fluorescence induction is not due to excitonic connectivity but rather changes in fluorescence yield upon QB site occupation; feedback regulation of ATP synthesis leads to oscillations.
Conclusions:
- Novel insights into Rubisco function and electron transport dynamics in intact leaves.
- The prevailing explanation for sigmoidal fluorescence induction is challenged, proposing a new mechanism.
- Photosynthetic electron transport is tightly regulated, with feedback mechanisms influencing ATP synthesis and leading to oscillations under specific conditions.
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