scholarly journals Heterocyst Thylakoid Bioenergetics

Life ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 13 ◽  
Author(s):  
Ann Magnuson
Keyword(s):  
Nitrogen Fixation ◽  
Electron Transport ◽  
Water Oxidation ◽  
Production Systems ◽  
Photosynthetic Electron Transport ◽  
Transport Pathways ◽  
Cell Factories ◽  
Diazotrophic Growth ◽  
Photosynthetic Water Oxidation

Heterocysts are specialized cells that differentiate in the filaments of heterocystous cyanobacteria. Their role is to maintain a microoxic environment for the nitrogenase enzyme during diazotrophic growth. The lack of photosynthetic water oxidation in the heterocyst puts special constraints on the energetics for nitrogen fixation, and the electron transport pathways of heterocyst thylakoids are slightly different from those in vegetative cells. During recent years, there has been a growing interest in utilizing heterocysts as cell factories for the production of fuels and other chemical commodities. Optimization of these production systems requires some consideration of the bioenergetics behind nitrogen fixation. In this overview, we emphasize the role of photosynthetic electron transport in providing ATP and reductants to the nitrogenase enzyme, and provide some examples where heterocysts have been used as production facilities.

scholarly journals Regulation of photosynthetic electron flow on dark to light transition by ferredoxin:NADP(H) oxidoreductase interactions

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Manuela Kramer ◽  
Melvin Rodriguez-Heredia ◽  
Francesco Saccon ◽  
Laura Mosebach ◽  
Manuel Twachtmann ◽  
...  
Keyword(s):  
Electron Transport ◽  
Electron Flow ◽  
Carbon Assimilation ◽  
Photosynthetic Electron Transport ◽  
Immunogold Labelling ◽  
Free Radical Damage ◽  
Transport Pathways ◽  
Photosynthetic Electron Flow ◽  
Radical Damage

During photosynthesis, electron transport is necessary for carbon assimilation and must be regulated to minimize free radical damage. There is a longstanding controversy over the role of a critical enzyme in this process (ferredoxin:NADP(H) oxidoreductase, or FNR), and in particular its location within chloroplasts. Here we use immunogold labelling to prove that FNR previously assigned as soluble is in fact membrane associated. We combined this technique with a genetic approach in the model plant Arabidopsis to show that the distribution of this enzyme between different membrane regions depends on its interaction with specific tether proteins. We further demonstrate a correlation between the interaction of FNR with different proteins and the activity of alternative photosynthetic electron transport pathways. This supports a role for FNR location in regulating photosynthetic electron flow during the transition from dark to light.

scholarly journals Symbiosis extended: exchange of photosynthetic O2 and fungal-respired CO2 mutually power metabolism of lichen symbionts

2019 ◽  
Vol 143 (3) ◽  
pp. 287-299 ◽  
Author(s):  
Marie-Claire ten Veldhuis ◽  
Gennady Ananyev ◽  
G. Charles Dismukes
Keyword(s):  
Electron Transport ◽  
Energy Conversion ◽  
Water Oxidation ◽  
Photosynthetic Electron Transport ◽  
Fluorescence Yield ◽  
Consecutive Series ◽  
Low Light ◽  
Conversion Rates ◽  
Algal Photosynthesis ◽  
Flavoparmelia Caperata

AbstractLichens are a symbiosis between a fungus and one or more photosynthetic microorganisms that enables the symbionts to thrive in places and conditions they could not compete independently. Exchanges of water and sugars between the symbionts are the established mechanisms that support lichen symbiosis. Herein, we present a new linkage between algal photosynthesis and fungal respiration in lichen Flavoparmelia caperata that extends the physiological nature of symbiotic co-dependent metabolisms, mutually boosting energy conversion rates in both symbionts. Measurements of electron transport by oximetry show that photosynthetic O2 is consumed internally by fungal respiration. At low light intensity, very low levels of O2 are released, while photosynthetic electron transport from water oxidation is normal as shown by intrinsic chlorophyll variable fluorescence yield (period-4 oscillations in flash-induced Fv/Fm). The rate of algal O2 production increases following consecutive series of illumination periods, at low and with limited saturation at high light intensities, in contrast to light saturation in free-living algae. We attribute this effect to arise from the availability of more CO2 produced by fungal respiration of photosynthetically generated sugars. We conclude that the lichen symbionts are metabolically coupled by energy conversion through exchange of terminal electron donors and acceptors used in both photosynthesis and fungal respiration. Algal sugars and O2 are consumed by the fungal symbiont, while fungal delivered CO2 is consumed by the alga.

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