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During photosynthetic water oxidation, the Mn4Ca cluster in Photosystem II progresses through five intermediate Si (i = 0–4) states. X-ray crystallography studies have reported the insertion of one new O ligand during the formation of the S3 state, but recent studies question the presence of this additional ligand based on cryo-EM and earlier room-temperature crystallography data. There is also controversy about whether the O-O bond interaction already occurs in the S3 state or in the subsequent S3 to S0 transition. Here we report conventional high-resolution data for the S1, S2, and S3 states to a resolution of ~1.9 Å, and anomalous diffraction data at two energies (9.5 keV and 7 keV), that was used to model the Mn positions, followed by determination of oxygen positions using the high-resolution maps. We show that the new oxygen atom, OX (or O6), in the S3 state is observable as a distinct peak without any restraints, confirming its ligation to Mn1 and Ca. The OX-O5 distance is ~2.1 Å, supporting no strong interaction between them in the S3 state, suggesting that if this is the O-O bond formation site, it is formed during the S3 to S0 transition initiated by the final oxidation of the cluster.

Essential plant nutrient elements are “eaten” along with light in the process of photosynthesis, primarily in the leaves. Two pigment-protein systems embedded in the thylakoid membrane, Photosystem I and Photosystem II, mediate light absorption, excitation energy transfer, primary photochemistry, electron transfer, oxidation of water, and reduction of NADP+ to NADPH. In addition to electron transfer, several membrane complexes release protons (H+) into the thylakoid lumen, generating an H+ gradient which is utilized by ATP synthase to produce ATP. Here, we describe how essential nutrient elements play vital roles in the metabolic pathways of photosynthesis and how their absences limit productivity because they are integral to the trafficking and turnover of metabolites. We provide an overview of key processes of photosynthesis, activation by metalloproteins, and the sites of their interactive roles in plants. An original open-source figure of the Z-Scheme of photosynthesis and the location of elements therein is provided for education and lectures. Signaling between nutrients, as well as crosstalk with plant growth regulators are important for directing metabolic pathways of photosynthates, such as sugars, highlighting the significance for management of minerals in the modulation of photosynthesis in the field. 

Three plant researchers describe in this book how plants emerged via the fusion of several different types of simple prokaryotic organisms and, through algae, evolved into land plants. During their evolution, they survived global ice ages, violent volcanic eruptions, and collisions with celestial bodies. The authors follow the development of landplants along various paths- some of which have ended. Horsetaills, quillworts and the Chinese temple tree are among the last remnants of once-great plant groups, whereas flowering plants now thrive, with their number of species exceeding all other plant groups combined.With the help of insects and fungi, flowering plants have reached this position. The final chapters provide a glimpse into the future of plants, our planet, and humanity, spanning 42 chapters in total.

This chapter compares two different techniques for monitoring photosynthetic O₂ production; the wide-spread Clark-type O₂ electrode and the more sophisticated membrane inlet mass spectrometry (MIMS) technique. We describe how a simple membrane inlet for MIMS can be made out of a commercial Clark-type cell and outline the advantages and drawbacks of the two techniques to guide researchers in deciding which method to use. Protocols and examples are given for measuring O₂ evolution rates and for determining the number of chlorophyll molecules per active photosystem II reaction center.

Green organisms evolve oxygen (O2) via photosynthesis and consume it by respiration. Generally, net O2 consumption only becomes dominant when photosynthesis is suppressed at night. Here, we show that green thylakoid membranes of Scots pine (Pinus sylvestris L) and Norway spruce (Picea abies) needles display strong O2 consumption even in the presence of light when extremely low temperatures coincide with high solar irradiation during early spring (ES). By employing different electron transport chain inhibitors, we show that this unusual light-induced O2 consumption occurs around photosystem (PS) I and correlates with higher abundance of flavodiiron (Flv) A protein in ES thylakoids. With P700 absorption changes, we demonstrate that electron scavenging from the acceptor-side of PSI via O2 photoreduction is a major alternative pathway in ES. This photoprotection mechanism in vascular plants indicates that conifers have developed an adaptative evolution trajectory for growing in harsh environments.

Photosynthetic water oxidation by Photosystem II (PSII) is a fascinating process because it sustains life on Earth and serves as a blue print for scalable synthetic catalysts required for renewable energy applications. The biophysical, computational, and structural description of this process, which started more than 50 years ago, has made tremendous progress over the past two decades, with its high-resolution crystal structures being available not only of the dark-stable state of PSII, but of all the semi-stable reaction intermediates and even some transient states. Here, we summarize the current knowledge on PSII with emphasis on the basic principles that govern the conversion of light energy to chemical energy in PSII, as well as on the illustration of the molecular structures that enable these reactions. The important remaining questions regarding the mechanism of biological water oxidation are highlighted, and one possible pathway for this fundamental reaction is described at a molecular level.

In general, the word, photosynthesis, is considered synonymous with oxygenic photosynthesis, a process by which cyanobacteria, algae, aquatic, and terrestrial plants produce oxygen and carbohydrates, using light (photons), water and carbon dioxide. Further, we have anoxygenic bacterial photosynthesis where oxygen is not evolved, but a substrate, other than water, is oxidized, and rhodopsin-type systems, where ATP is produced. In principle, one could expand the concept of the term photosynthesis, provided appropriate caveats are added, to include lightdriven assimilation of molecular nitrogen, photoproduction of molecular hydrogen, and even synthesis of vitamin D in skin. We conclude with a glimpse of the rapidly developing field of artificial photosynthesis.

The regulation of photosynthetic machinery with a nonoxidative approach is a powerful but challenging strategy for the selective inhibition of bloom-forming cyanobacteria. Acetylacetone (AA) was recently found to be a target-selective cyanocide for Microcystis aeruginosa, but the cause and effect in the studied system are still unclear. By recording of the chemical fingerprints of the cells at two treatment intervals (12 and 72 h with 0.1 mM AA) with omics assays, the molecular mechanism of AA in inactivating Microcystis aeruginosa was elucidated. The results clearly reveal the effect of AA on ferredoxin and the consequent effects on the physiological and biochemical processes of Microcystis aeruginosa. In addition to its role as an electron acceptor of photosystem I, ferredoxin plays pivotal roles in the assimilation of nitrogen in cyanobacterial cells. The effect of AA on ferredoxin and on nonheme iron of photosystem II first cut off the photosynthetic electron transfer flow and then interrupted the synthesis of adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH), which ultimately might affect carbon fixation and nitrogen assimilation metabolisms. The results here provide missing pieces in the current knowledge on the selective inhibition of cyanobacteria, which should shed light on the better control of harmful blooms.

On the occasion of the 90th birthday of Govindjee, Professor Emeritus of Plant Biology, Biochemistry, and Biophysics, the University of Illinois at Urbana-Champaign (UIUC), over 100 celebrants have sent felicitations and messages to thank him for mentoring, nurturing, and building the community of photosynthesis researchers belonging to four generations; and in making the scientific knowledge accessible to students and young researchers via his monumental writings and editorial contributions. Govindjee joined UIUC in September of 1956 to study as a graduate student in the laboratory of Robert Emerson. In 1961, he joined UIUC as an Assistant Professor and retired as a full professor in 1999. He is well-known for pioneering work in oxygenic photosynthesis, leading to the current Z-scheme, and for his breakthrough advances concerning light harvesting, primary charge separation, the role of bicarbonate on the two-electron gate of photosystem II, water oxidation, nonphotochemical quenching, and the use of biophysical techniques, such as prompt fluorescence, delayed fluorescence, thermoluminescence, and nuclear magnetic resonance. Today, despite his retirement, Govindjee continues to explore several important questions in the field of photosynthesis and documents the history of science. This tribute, in turn, attempts to capture scientific collaborations, as well as scholarly and personal contributions made by Govindjee to the lives of hundreds of scholars and students worldwide.

We celebrate Govindjee, Professor Emeritus of Plant Biology, Biochemistry, and Biophysics, University of Illinois at Urbana-Champaign, on the occasion of his 90th birthday. He is renowned for his pioneering work in the discovery of the two-light reactions and two photosystems, PSI and PSII, leading to the Z-scheme of the electron transport chain; and for breakthrough advances in oxygenic photosynthesis. Govindjee’s publications have been cited over 26,000 times. He is an elected Fellow of the American Association of the Advancement of Science, USA; National Academy of Agriculture Science, India; and National Academy of Sciences, India; and beyond that, he has received many awards from scientific societies, most recently, the ISPR Lifetime Achievement Award, August 2022. As even today, Govindjee continues to actively contribute to the field, we highlight the major events in his colorful personal and rigorous scientific life with emphasis on the work done after his retirement, and as well, his prodigious accomplishments as teacher, editor, and science historian.