New insights about photosynthetic processes in natural conditions

​Press release by University of Turku

Researchers of the University of Turku, Finland and Wageningen University, the Netherlands, have made an important step in describing how sunlight is absorbed and distributed in the photosynthetic machinery of cyanobacterial cells during light fluctuations. Previously photo-regulatory mechanisms have been mainly studied during more artificial light conditions.

– Due to the complexity of the photo-regulatory mechanisms, most of the research makes use of highly specific, well-defined artificial conditions, such as single-wavelength light and the presence of chemicals to regulate the energy flow. In our study we use light conditions which are found in the environment, says Doctoral Candidate Luca Bersanini from the University of Turku.

A decisive  biophysical approach together with biochemical methods was applied by Volha Chukhutsina (Wageningen University) and Luca Bersanini (University of Turku) to follow the energy transfer from light towards photosynthetic machinery on a 10^-12 second timescale.
 
The new study uses “natural” light conditions: a dark-to-light scheme typical of what the organisms experience when external factors move them between these regimes in the sea.

– In darkness, the cells accumulate many electrons due to respiratory processes. These electrons can be re-used for the creation of energy-rich species during photosynthesis, Bersanini says.

The study shows that in darkness, the cells seem to “get ready” for an increase in light intensity by adopting a larger light-harvesting antenna.

– In this way, during the first seconds after the light appears, they can immediately utilize the electron pool very efficiently to re-create energy-rich molecules, Bersanini says.

Cyanobacteria contribute substantially to the global fixation of carbon dioxide, and knowledge about their photosynthetic strategies may contribute to original solutions for energy sustainability.

Cyanobacteria are ancient single-celled aquatic organisms, also known as blue-green algae: their blue color arises from their big “light-harvesting” pigment-protein complexes.

The aquatic environment poses various challenges to the photosynthetic apparatus. In the upper water layers, one of the main challenges is the fluctuating incident light intensity. Waves and currents cause scattering of the light in waters and, in particular, suddenly increased light intensities can cause imbalances in the photosynthetic apparatus. It is well-known that the cells have regulatory mechanisms to rapidly modulate the amount of absorbed light by rearranging the light-harvesting machinery, but in this study our researchers shed light on a new mechanism of adaptation.

The study was published in Nature Scientific Reports: http://www.nature.com/articles/srep14193