11th International Conference on "Photosynthesis and Hydrogen Energy Research for Sustainability".

All aerobic life on Earth depends on oxygenic photosynthesis, occurring in both prokaryotic and eukaryotic organisms. This process can be divided into light reactions and carbon fixation. This special issue is a result of the International Conference on "Photosynthesis and Hydrogen Energy Research for Sustainability 2023," held in honor of Robert Blankenship, Gyozo Garab, Michael Grätzel, Norman Hüner, and Gunnar Öquist. After extensive discussions on various aspects of photosynthesis and hydrogen energy, eight high-quality papers were selected. These papers cover studies on abiotic stress, an overview of photosynthesis, thylakoid membrane lipid organization, energy transfer, and the genomics of both prokaryotic and eukaryotic photosynthesis, as well as biohydrogen production from cyanobacteria. The authors used new methods and techniques, likely bringing fresh ideas for improving biomass and crop yield.

Access to the Antenna System of Photosystem I via Single-Molecule Excitation-Emission Spectroscopy.

In the development of single-molecule spectroscopy, the simultaneous detection of the excitation and emission spectra has been limited. The fluorescence excitation spectrum based on background-free signals is compatible with the fluorescence-emission-based detection of single molecules and can provide insight into the variations in the input energy of the different terminal emitters. Here, we implement single-molecule excitation-emission spectroscopy (SMEES) for photosystem I (PSI) via a cryogenic optical microscope. To this end, we extended our line-focus-based excitation-spectral microscope system to the cryogenic temperature-compatible version. PSI is one of the two photosystems embedded in the thylakoid membrane in oxygen-free photosynthetic organisms. PSI plays an essential role in electron transfer in the photosynthesis reaction. PSIs of many organisms contain a few red-shifted chlorophylls (Chls) with much lower excitation energies than ordinary antenna Chls. The fluorescence emission spectrum originates primarily from the red-shifted Chls, whereas the excitation spectrum is sensitive to the antenna Chls that are upstream of red-shifted Chls. Using SMEES, we obtained the inclining two-dimensional excitation-emission matrix (2D-EEM) of PSI particles isolated from a cyanobacterium, Thermosynechococcus vestitus (equivalent to elongatus), at about 80 K. Interestingly, by decomposing the inclining 2D-EEMs within time course observation, we found prominent variations in the excitation spectra of the red-shifted Chl pools with different emission wavelengths, strongly indicating the variable excitation energy transfer (EET) pathway from the antenna to the terminal emitting pools. SMEES helps us to directly gain information about the antenna system, which is fundamental to depicting the EET within pigment-protein complexes.

Reddening of the Unicellular Green Alga Euglena gracilis by Dried Bonito Stock and Intense Red Light Irradiation.

This study confirms for the first time that the significant red coloration of Euglena gracilis is induced by bonito stock (BS), a traditional Japanese food, and intense red light exposure (605~660 nm, 1000~1300 µmol photons/m2/s). Under the condition, excessive photosynthetic activity destroyed many chloroplasts, while carotenoids were maintained, resulting in the formation of reddened cells. The HPLC analysis revealed that diadinoxanthin was the primary carotenoid present in reddened cells. Additionally, an undefined xanthophyll, not produced under normal culture conditions, was synthesized and suggested to contain a C=O bond. While it has been reported that strong light stress can increase the total carotenoid content of cells, this study did not verify this claim, and it should be investigated further in future research. Under white light irradiation conditions (90 µmol photons/m2/s) in BS medium, no reddening of cells was observed, and good growth was achieved (over four times the cell density in CM medium on the seventh day). This cell suspension is considered to have a high nutritional value because it is composed of functional food, BS and E. gracilis. The fact that this method does not involve genetic modification suggests the possibility of industrial applications, including food use, even in reddened cells.

International conference on "Photosynthesis and Hydrogen Energy Research for Sustainability-2023": in honor of Robert Blankenship, Gyozo Garab, Michael Grätzel, Norman Hüner and Gunnar Öquist.

The 11th International Photosynthesis Conference on Hydrogen Energy Research and Sustainability 2023 was organized in honor of Robert Blankenship, Gyozo Garab, Michael Grätzel, Norman Hüner, and Gunnar Öquist, in Istanbul, Türkiye at Bahçesehir University Future Campus from 03 to 09 July 2023. It was jointly supported by the International Society of Photosynthesis Research (ISPR) and the International Association for Hydrogen Energy (IAHE). In this article we provide brief details of the conference, its events, keynote speakers, and the scientific contribution of scientists honored at this conference. Further, we also describe the participation of young researchers, their talks, and their awards.