Current challenges in photosynthesis: from natural to artificial

Photosynthesis is a process by which plants, algae, cyanobacteria, and anoxygenic photosynthetic bacteria capture and store solar energy on a massive scale, in particular via the water-splitting chemistry (Hoganson and Babcock, 1997; Blankenship, 2002; Ferreira et al., 2004; Loll et al., 2005; Yano et al., 2006; Umena et al., 2011). It is the most important reaction on Earth, estimated to produce more than 100 billion tons of dry biomass annually; this means that photosynthesis is producing biomass equal to two Egyptian pyramids per hour. But, this will not be enough to sustain life on Earth by the year 2050. The global fossil fuels on which we currently depend are derived from millions of years of past photosynthetic activity. The fossil energy fuels are limited and must be replaced by renewable and environment-friendly energy source to support and sustain life on Earth (Lewis and Nocera, 2006; Blankenship et al., 2011). To address this immediate energy crisis, worldwide efforts are being made on artificial photosynthesis using the principles and mechanisms observed in nature (Brimblecombe et al., 2009; McConnell et al., 2010; Kanady et al., 2011; Wiechen et al., 2012; Najafpour et al., 2013). It is not a matter of mimicking natural photosynthesis, but to use its current knowledge to improve photosynthesis itself, as well as to produce biofuels, including hydrogen evolution by artificial means (Barber, 2009; Hou, 2010; Nocera, 2012; He et al., 2013).

This book contains 10 chapters and presents recent advances in photosynthesis and artificial photosynthesis. It starts with two opinion articles on possible strategies to improve photosynthesis in plants and fascinating mechanisms of unidirectional photodamage of pheophytin in photosynthesis. The idea that plant photosynthesis is maximized due to the perfect evolution might be faulty. Leister evaluated and argued the issue openly and proposed that improvement of photosynthesis can be made by synthetic biology including genetic engineering, redesign or de novo creation of entire photosystems as well as conventional breeding (Leister, 2012). Unidirectional photodamage of a pheophytin molecule in photosystem II and purple bacterial reaction centers was observed. The mysterious phenomena were analyzed and discussed in terms of different possible functions of the pheophytin in photosynthesis (Hou, 2014).

The book is followed by four review articles that discuss the current state of research on: photosynthetic water oxidation in natural and artificial photosynthesis, as obtained by mass spectrometry (MS) and Fourier transform infrared spectroscopy (FTIR); functional models of thylakoid lumen; and horizontal gene transfer in photosynthetic eukaryotes. The time-resolved isotope-ratio membrane-inlet mass spectrometry (TR-IR-MIMS) is able to determine the isotopic composition of gaseous products. Shevela et al briefly introduced the key aspects of the methodology, summarized the recent results on the mechanisms and pathways of oxygen formation in PS II using this unique technique and outlined the future perspectives of the application in water splitting chemistry (Shevela and Messinger, 2013) Another unique technique in probing the mechanism of water oxidation in PS II is the light-induced FTIR difference spectroscopy. Chu reviewed the recent fruitful structural data, and believed that the FTIR will continue to provide vital structural and mechanistic insights into the water-splitting process in PS II together with isotopic labeling, site-directed mutagenesis, model compound studies, and computational calculation (Chu, 2013). The thylakoid lumen offers the environment for oxygen evolution, electron transfer, and photoprotection in photosynthesis. Jarvi et al evaluated the recent studies of many lumen proteins and highlighted the importance of the thiol-disulfide modulation in controlling the functions of the thylakoid lumen proteins and their pathways of photosynthesis (Järvi et al., 2013). Qiu et al discussed that importance of the horizontal gene transfer (HGT) in enriching the algal genomes and proposed that the alga endosymbionts may be the HGT vectors in photosynthetic eukaryotes (Qiu et al., 2013).

Finally, the book offers four research articles, which focus on FTIR studies on photosynthetic reaction centers, functions of thylakoid protein kinases STN7 and STN8, photosynthesis acclimation of maize seedlings, and characterization of the newly discovered chlorophyll f-containing cyanobacterium Halomicronema hongdechloris. The computational calculation (ONIOM) is increasingly critical in interpreting the FTIR data in elucidating the structural and functional relationship in photosynthesis. Zhao et al using ONIOM type calculation to simulate isotope edited FTIR difference spectra for reaction centers with a variety of foreign quinones in the Q_A site and allows a direct assessment of the appropriateness of previous IR assignments and suggestions (Zhao et al., 2013). The protein kinases STN7 and STN8 are predominately responsible for the thylakoid phosphorylation in PS II. Wunder et al reported the effects of the STN8 expression levels on the formation and modulation of thylakoid proteins and kinases (Wunder et al., 2013). Hirth et al assessed the photosynthetic acclimation responses of the C3 and C4 plants under simulated field light conditions (Hirth et al., 2013). Recently a chlorophyll f (Chl f) in cyanobacterium Halomincronema hongdechloris was identified and has the most red-shifted absorption peak of 707 nm in oxygenic photosynthesis (Chen et al., 2010), which may enhance the potential photosynthesis efficiency for solar fuel production. The Halomincronema hongdechloris was characterized upon the exposure to the different light, pH, salinity, temperature, and nutrition to achieve the optimizing growth culture conditions (Li et al., 2014).

Due to the extremely limited time frame for collecting manuscripts and the strict deadline for publishing this book, several planned manuscripts by world leaders, who had agreed to contribute, are unfortunately not included in this book. Thus, the current book provides a snapshot of the latest work in photosynthesis research. To obtain complete information on the current progress in the field of photosynthesis, we highly recommend reviews and research articles, published in 2013, in two volumes of Photosynthesis Research (Allakhverdiev et al., 2013a,b)

In conclusion, the book provides readers with some of the most recent and exciting breakthroughs from natural to artificial photosynthesis, discusses the potential limitations of the results, and addresses open questions in photosynthesis and energy research. It is written by 31 young active scientists and established leading experts from Australia, Finland, Germany, Sweden, Taiwan, and the United States. We hope that this book is able to provide novel and insightful information to readers and stimulate the future research endeavors in the photosynthesis community.

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