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A guide to environmental fluctuations that examines photosynthesis under both controlled and stressed conditions Photosynthesis, Productivity and Environmental Stress is a much-needed guide that explores the topics related to photosynthesis (both terrestrial and aquatic) and puts the focus on the basic effect of environmental fluctuations. The authors—noted experts on the topic—discuss photosynthesisunder both controlled and stressed conditions and review new techniques for mitigating stressors including methods such as transgeneics, proteomics, genomics, ionomics, metabolomics, micromics, and more. In order to feed our burgeoning world population, it is vital that we must increase food production. Photosynthesis is directly related to plant growth and crop production and any fluctuation in the photosynthetic activity imposes great threat to crop productivity. Due to the environmental fluctuations plants are often exposed to the different environmental stresses that cause decreased photosynthetic rate and problems in the plant growth and development. This important book addresses this topic and: * Covers topics related to terrestrial and aquatic photosynthesis * Highlights the basic effect of environmental fluctuations * Explores common stressors such as drought, salinity, alkalinity, temperature, UV-radiations, oxygen deficiency, and more * Contains methods and techniques for improving photosynthetic efficiency for greater crop yield Written for biologists and environmentalists, Photosynthesis, Productivity and Environmental Stress offers an overview of the stressors affecting photosynthesis and includes possible solutions for improved crop production.

In plants and algae, light serves both as the energy source for photosynthesis and a biological signal that triggers cellular responses via specific sensory photoreceptors. Red light is perceived by bilin-containing phytochromes and blue light by the flavin-containing cryptochromes and/or phototropins (PHOTs), the latter containing two photosensory light, oxygen, or voltage (LOV) domains. Photoperception spans several orders of light intensity, ranging from far below the threshold for photosynthesis to values beyond the capacity of photosynthetic CO2 assimilation. Excess light may cause oxidative damage and cell death, processes prevented by enhanced thermal dissipation via high-energy quenching (qE), a key photoprotective response. Here we show the existence of a molecular link between photoreception, photosynthesis, and photoprotection in the green alga Chlamydomonas reinhardtii. We show that PHOT controls qE by inducing the expression of the qE effector protein LHCSR3 (light-harvesting complex stress-related protein 3) in high light intensities. This control requires blue-light perception by LOV domains on PHOT, LHCSR3 induction through PHOT kinase, and light dissipation in photosystem II via LHCSR3. Mutants deficient in the PHOT gene display severely reduced fitness under excessive light conditions, indicating that the sensing, utilization, and dissipation of light is a concerted process that plays a vital role in microalgal acclimation to environments of variable light intensities.

Photosynthesis: a supercomplex of supercomplexes During photosynthesis, light energy is utilized by photosystems 1 (PSI) and II (PSII), located in the thylakoid membranes of chloroplasts, to establish an electron flow that ultimately results in the production of ATP and NADPH. Two modes of electron flow exist — a linear electron flow and a cyclic electron flow. The latter pathway generates more ATP but the molecular components of the supercomplex involved in the process have remained elusive. This issue is now addressed directly in the green alga Chlamydomonas reinhardtii . A combination of biochemical and spectroscopic techniques reveals the supercomplex that drives cyclic electron flow to be made up not only of the photosystem/peripheral antenna supercomplex, but also of two known redox proteins — cytochrome b 6 f complex and ferredoxin-NADPH oxidoreductase (FNR) — with a few small proteins as well. During photosynthesis, light energy is used by photosystems I and II to establish electron flow, which ultimately results in the production of ATP and NADPH. Two modes of electron flow exist, a linear electron flow and a cyclic electron flow (CEF). The latter pathway generates more ATP, but its molecular components have been elusive. Here, a combination of biochemical and spectroscopic techniques has been used to identify the supercomplex that drives CEF in the green alga Chlamydomonas reinhardtii . Photosynthetic light reactions establish electron flow in the chloroplast’s thylakoid membranes, leading to the production of the ATP and NADPH that participate in carbon fixation. Two modes of electron flow exist—linear electron flow (LEF) from water to NADP + via photosystem (PS) II and PSI in series 1 and cyclic electron flow (CEF) around PSI (ref. 2 ). Although CEF is essential for satisfying the varying demand for ATP, the exact molecule(s) and operational site are as yet unclear. In the green alga Chlamydomonas reinhardtii , the electron flow shifts from LEF to CEF on preferential excitation of PSII (ref. 3 ), which is brought about by an energy balancing mechanism between PSII and PSI (state transitions 4 ). Here, we isolated a protein supercomplex composed of PSI with its own light-harvesting complex (LHCI), the PSII light-harvesting complex (LHCII), the cytochrome b 6 f complex (Cyt bf ), ferredoxin (Fd)-NADPH oxidoreductase (FNR), and the integral membrane protein PGRL1 (ref. 5 ) from C. reinhardtii cells under PSII-favouring conditions. Spectroscopic analyses indicated that on illumination, reducing equivalents from downstream of PSI were transferred to Cyt bf , whereas oxidised PSI was re-reduced by reducing equivalents from Cyt bf , indicating that this supercomplex is engaged in CEF ( Supplementary Fig. 1 ). Thus, formation and dissociation of the PSI–LHCI–LHCII–FNR–Cyt bf –PGRL1 supercomplex not only controlled the energy balance of the two photosystems, but also switched the mode of photosynthetic electron flow.

The purpose of this paper is to review the scientific results and summarise the emerging topic of the effects of statistic magnetic field on the structure, biochemical activity, and gene expression of plants. The literature on the subject reports a wide range of possibilities regarding the use of the magnetic field to modify the properties of plant cells. MFs have a significant impact on the photosynthesis efficiency of the biomass and vigour accumulation indexes. Treating plants with SMFs accelerates the formation and accumulation of reactive oxygen species. At the same time, the influence of MFs causes the high activity of antioxidant enzymes, which reduces oxidative stress. SMFs have a strong influence on the shape of the cell and the structure of the cell membrane, thus increasing their permeability and influencing the various activities of the metabolic pathways. The use of magnetic treatments on plants causes a higher content of proteins, carbohydrates, soluble and reducing sugars, and in some cases, lipids and fatty acid composition and influences the uptake of macro- and microelements and different levels of gene expression. In this study, the effect of MFs was considered as a combination of MF intensity and time exposure, for different varieties and plant species. The following article shows the wide-ranging possibilities of applying magnetic fields to the dynamics of changes in the life processes and structures of plants. Thus far, the magnetic field is not widely used in agricultural practice. The current knowledge about the influence of MFs on plant cells is still insufficient. It is, therefore, necessary to carry out detailed research for a more in-depth understanding of the possibilities of modifying the properties of plant cells and achieving the desired effects by means of a magnetic field.

A new approach, time-resolved serial femtosecond crystallography, is used to view the intermediate states of a photosystem complex following illumination, shedding light on proton transfer and O=O bond formation. Bond formation in photosystem II Technical developments, such as X-ray free electron lasers (XFEL), allow for a more detailed view of the structure of the photosystem complexes, making it possible to get a glimpse of the mechanisms of proton transfer and bond formation. Jian-Ren Shen and colleagues use a new approach, time-resolved serial femtosecond crystallography, with X-ray free electron lasers to view the intermediate states formed after two-flash illumination. Upon illumination, the authors see that the disappearance of one water molecule relocates another water molecule towards an oxygen atom, in a manner that may reflect proton transfer. They also gain evidence for the inclusion of a new oxygen atom that would be positioned to form an O=O bond that has been hypothesized but never previously detected. These insights increase our understanding of the mechanism of water oxidation in photosystem II. Photosystem II (PSII) is a huge membrane-protein complex consisting of 20 different subunits with a total molecular mass of 350 kDa for a monomer. It catalyses light-driven water oxidation at its catalytic centre, the oxygen-evolving complex (OEC) 1 , 2 , 3 . The structure of PSII has been analysed at 1.9 Å resolution by synchrotron radiation X-rays, which revealed that the OEC is a Mn 4 CaO 5 cluster organized in an asymmetric, ‘distorted-chair’ form 4 . This structure was further analysed with femtosecond X-ray free electron lasers (XFEL), providing the ‘radiation damage-free’ 5 structure. The mechanism of O=O bond formation, however, remains obscure owing to the lack of intermediate-state structures. Here we describe the structural changes in PSII induced by two-flash illumination at room temperature at a resolution of 2.35 Å using time-resolved serial femtosecond crystallography with an XFEL provided by the SPring-8 ångström compact free-electron laser. An isomorphous difference Fourier map between the two-flash and dark-adapted states revealed two areas of apparent changes: around the Q B /non-haem iron and the Mn 4 CaO 5 cluster. The changes around the Q B /non-haem iron region reflected the electron and proton transfers induced by the two-flash illumination. In the region around the OEC, a water molecule located 3.5 Å from the Mn 4 CaO 5 cluster disappeared from the map upon two-flash illumination. This reduced the distance between another water molecule and the oxygen atom O4, suggesting that proton transfer also occurred. Importantly, the two-flash-minus-dark isomorphous difference Fourier map showed an apparent positive peak around O5, a unique μ 4 -oxo-bridge located in the quasi-centre of Mn1 and Mn4 (refs 4 , 5 ). This suggests the insertion of a new oxygen atom (O6) close to O5, providing an O=O distance of 1.5 Å between these two oxygen atoms. This provides a mechanism for the O=O bond formation consistent with that proposed previously 6 , 7 .

Microalgae are considered to be a dual solution for CO[sub.2] fixation and biogas slurry purification due to their high photosynthetic efficiency and strong environmental adaptability. However, their application is constrained by the low solubility of CO[sub.2] in the solution environment, which restricts microalgal growth, resulting in low biomass production and poor slurry purification efficiency. In this study, we developed MgFe layered double hydroxide (LDH) that spontaneously combined with Chlorella pyrenoidosa to help it concentrate CO[sub.2] , thereby increasing biomass yield and purification capacity for food waste biogas slurry. The prepared MgFe-LDH exhibited a typical layered structure with a CO[sub.2] adsorption capacity of 4.44 mmol/g. MgFe-LDH and C. pyrenoidosa carried opposite charges, enabling successful self-assembly via electrostatic interaction. Compared with the control, the addition of 200 ppm MgFe-LDH increased C. pyrenoidosa biomass and pigment content by 36.82% and 63.05%, respectively. The removal efficiencies of total nitrogen, total phosphorus, and ammonia nitrogen in the slurry were enhanced by 20.04%, 31.54% and 14.57%, respectively. The addition of LDH effectively alleviated oxidative stress in C. pyrenoidosa and stimulated the secretion of extracellular polymeric substances, thereby enhancing the stress resistance and pollutant adsorption capabilities. These findings provided a new strategy for the industrial application of microalgal technology in CO[sub.2] fixation and wastewater treatment.

The Precambrian: a green alternative Dozens of studies in the past decade have reported carbon isotope variations in Neoproterozoic carbonate rocks and linked them to perturbations of the global carbon cycle. Paul Knauth and Martin Kennedy have taken a sideways look at the data by concentrating on the oxygen isotope measurements (for over 20,000 samples) that are necessarily obtained as part of the carbon isotope analysis but are often overlooked. They arrive at the striking conclusion that the combined oxygen and carbon isotope systematics are identical to those of well-understood Phanerozoic examples that lithified in coastal pore fluids receiving a groundwater influx of photosynthetic carbon from terrestrial phytomass. Rather than being perturbations to the carbon cycle, widely reported decreases in 13 C/ 12 C in Neoproterozoic carbonates are more easily interpreted by analogy to the Phanerozoic examples. And that could suggest a 'greening' of the Earth under a ground-hugging mat of photosynthetic algae, mosses and fungi in the late Precambrian. Such an event, producing oxygen and phytomass, could even be indirectly responsible for the critical transition from the essentially microbial world of the Precambrian to the metazoan world of the Cambrian. The low 13 C/ 12 C ratio in some Neoproterozoic carbonates is considered to be evidence of carbon cycle perturbations unique to the Precambrian. Here, all published oxygen and carbon isotope data for Neoproterozoic marine carbonates are compiled. The combined isotope systematics are found to be identical to those of well-understood Phanerozoic examples, suggesting an influx of photosynthetic carbon rather than perturbations to the carbon cycle — and implying an explosion of photosynthesizing communities on late Precambrian land surfaces. Many aspects of the carbon cycle can be assessed from temporal changes in the 13 C/ 12 C ratio of oceanic bicarbonate. 13 C/ 12 C can temporarily rise when large amounts of 13 C-depleted photosynthetic organic matter are buried at enhanced rates 1 , and can decrease if phytomass is rapidly oxidized 2 or if low 13 C is rapidly released from methane clathrates 3 . Assuming that variations of the marine 13 C/ 12 C ratio are directly recorded in carbonate rocks, thousands of carbon isotope analyses of late Precambrian examples have been published to correlate these otherwise undatable strata and to document perturbations to the carbon cycle just before the great expansion of metazoan life. Low 13 C/ 12 C in some Neoproterozoic carbonates is considered evidence of carbon cycle perturbations unique to the Precambrian. These include complete oxidation of all organic matter in the ocean 2 and complete productivity collapse such that low- 13 C/ 12 C hydrothermal CO 2 becomes the main input of carbon 4 . Here we compile all published oxygen and carbon isotope data for Neoproterozoic marine carbonates, and consider them in terms of processes known to alter the isotopic composition during transformation of the initial precipitate into limestone/dolostone. We show that the combined oxygen and carbon isotope systematics are identical to those of well-understood Phanerozoic examples that lithified in coastal pore fluids, receiving a large groundwater influx of photosynthetic carbon from terrestrial phytomass. Rather than being perturbations to the carbon cycle, widely reported decreases in 13 C/ 12 C in Neoproterozoic carbonates are more easily interpreted in the same way as is done for Phanerozoic examples. This influx of terrestrial carbon is not apparent in carbonates older than ∼850 Myr, so we infer an explosion of photosynthesizing communities on late Precambrian land surfaces. As a result, biotically enhanced weathering generated carbon-bearing soils on a large scale and their detrital sedimentation sequestered carbon 5 . This facilitated a rise in O 2 necessary for the expansion of multicellular life.

This review analyzes data available in the literature on the rates, characteristics, and mechanisms of oxygen reduction to a superoxide anion radical at the sites of photosynthetic electron transport chain where this reduction has been established. The existing assumptions about the role of the components of these sites in this process are critically examined using thermodynamic approaches and results of the recent studies. The process of O2 reduction at the acceptor side of PSI, which is considered the main site of this process taking place in the photosynthetic chain, is described in detail. Evolution of photosynthetic apparatus in the context of controlling the leakage of electrons to O2 is explored. The reasons limiting application of the results obtained with the isolated segments of the photosynthetic chain to estimate the rates of O2 reduction at the corresponding sites in the intact thylakoid membrane are discussed.

Improving nitrogen uptake efficiency by citrus in Mediterranean areas, where this crop predominates, is crucial for reducing ground-water pollution and enhancing environmental sustainability. This aligns with the Farm to Fork Strategy (European Green Deal) objectives, which aim to reduce the use of mineral fertilizers by up to 20% and to eliminate soil contamination from nitrogen entirely. In this context, exploring the potential of plant growth-promoting bacteria application to reduce nutrient inputs is a promising opportunity. The objective of the present study was to evaluate the effect of two Bacillus subtilis strains either individually inoculated or in combination with Saccharomyces cerevisiae on 15N-labeled fertilizer uptake efficiency and physiological parameters. Individual inoculations positively affected tree water potential, leaf chlorophyll concentrations (SPAD-values) and photosynthetic performance, enhancing tree growth. Fertilizer-15N use efficiency increased, as did phosphorus and potassium uptakes. Conversely, no response was observed in the trees co-inoculated with S cerevisiae. Therefore, PGPB can be considered an interesting means to reduce reliance on synthetic fertilizers in citrus orchards, minimizing the environmental impact and promoting sustainable production practices.