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Here, we describe a model of C3, C3–C4 intermediate, and C4 photosynthesis that is designed to facilitate quantitative analysis of physiological measurements. The model relates the factors limiting electron transport and carbon metabolism, the regulatory processes that coordinate these metabolic domains, and the responses to light, carbon dioxide, and temperature. It has three unique features. First, mechanistic expressions describe how the cytochrome b6f complex controls electron transport in mesophyll and bundle sheath chloroplasts. Second, the coupling between the mesophyll and bundle sheath expressions represents how feedback regulation of Cyt b6f coordinates electron transport and carbon metabolism. Third, the temperature sensitivity of Cyt b6f is differentiated from that of the coupling between NADPH, Fd, and ATP production. Using this model, we present simulations demonstrating that the light dependence of the carbon dioxide compensation point in C3–C4 leaves can be explained by co-occurrence of light saturation in the mesophyll and light limitation in the bundle sheath. We also present inversions demonstrating that population-level variation in the carbon dioxide compensation point in a Type I C3–C4 plant, Flaveriachloraefolia, can be explained by variable allocation of photosynthetic capacity to the bundle sheath. These results suggest that Type I C3–C4 intermediate plants adjust pigment and protein distributions to optimize the glycine shuttle under different light and temperature regimes, and that the malate and aspartate shuttles may have originally functioned to smooth out the energy supply and demand associated with the glycine shuttle. This model has a wide range of potential applications to physiological, ecological, and evolutionary questions.

Domestication involves dramatic phenotypic and physiological diversifications due to successive selection by breeders toward high yield and quality. Although photosynthetic nitrogen use efficiency (PNUE) is a major trait for understanding leaf nitrogen economy, it is unclear whether PNUE of cotton has been improved under domestication. Here, we investigated the effect of domestication on nitrogen allocation to photosynthetic machinery and PNUE in 25 wild and 37 domesticated cotton genotypes. The results showed that domesticated genotypes had higher nitrogen content per mass (Nm), net photosynthesis under saturated light (Asat), and PNUE but similar nitrogen content per area (Na) compared with wild genotypes. As expected, in both genotypes, PNUE was positively related to Asat but negatively correlated with Na. However, the relative contribution of Asat to PNUE was greater than the contribution from Na. Domesticated genotypes had higher nitrogen allocation to light-harvesting (NL, nitrogen in light-harvesting chlorophyll-protein complex), to bioenergetics (Nb, total nitrogen of cytochrome f, ferredoxin NADP reductase, and the coupling factor), and to Rubisco (Nr) than wild genotypes; however, the two genotype groups did not differ in PNUEp, the ratio of Asat to Np (itself the sum of NL, Nb, and Nr). Our results suggest that more nitrogen allocation to photosynthetic machinery has boosted Asat under cotton domestication. Improving the efficiency of nitrogen use in photosynthetic machinery might be future aim to enhance Asat of cotton.

The complete genome sequence of the thermophilic purple sulfur bacterium Thermochromatium tepidum strain MCT (DSM 3771T) is described and contrasted with that of its mesophilic relative Allochromatium vinosum strain D (DSM 180T) and other Chromatiaceae. The Tch. tepidum genome is a single circular chromosome of 2,958,290 base pairs with no plasmids and is substantially smaller than the genome of Alc. vinosum. The Tch. tepidum genome encodes two forms of RuBisCO and contains nifHDK and several other genes encoding a molybdenum nitrogenase but lacks a gene encoding a protein that assembles the Fe–S cluster required to form a functional nitrogenase molybdenum-iron cofactor, leaving the phototroph phenotypically Nif–. Tch. tepidum contains genes necessary for oxidizing sulfide to sulfate as photosynthetic electron donor but is genetically unequipped to either oxidize thiosulfate as an electron donor or carry out assimilative sulfate reduction, both of which are physiological hallmarks of Alc. vinosum. Also unlike Alc. vinosum, Tch. tepidum is obligately phototrophic and unable to grow chemotrophically in darkness by respiration. Several genes present in the Alc. vinosum genome that are absent from the genome of Tch. tepidum likely contribute to the major physiological differences observed between these related purple sulfur bacteria that inhabit distinct ecological niches.

In this study, we studied and developed the modification schemes of environmentally friendly substitutes of neonicotinoid insecticides (NNIs) along with the regulatory measures that effectively enhanced the synergistic degradation of NNIs by soil rhizobia and carbon-fixing bacteria. Firstly, the binding ability of NNIs to the two key proteins was characterized by molecular docking; secondly, the mean square deviation decision method, which is a comprehensive evaluation method, was used to investigate the binding ability of NNI molecules with the two Rubisco rate-limiting enzymes. The three-dimensional quantitative structure-activity relationship (3D-QSAR) model was established for the synergistic degradation and single effect of rhizobia and carbon-fixing bacteria. Finally, after combining the 3D-QSAR model with a contour map analysis of the synergistic degradation effect of soil rhizobia and carbon-fixing bacteria, 102 NNI derivatives were designed. Flonicamid-36 and other four NNI derivatives passed the functional and environmentally friendly evaluation. Taguchi orthogonal experiment and factorial experiment-assisted molecular dynamics method were used to simulate the effects of 32 regulation schemes on the synergistic degradation of NNIS and its derivatives by rhizobia and carbon fixing bacteria. The synergistic degradation capacity of soil rhizobia and carbon-fixing bacteria was increased to 33.32% after right nitrogen supplementation. This indicated that supplementing the correct amount of nitrogen in the soil environment was beneficial to the microbial degradation of NNIs and their derivatives.

Increasing temperature is a key component of global climate change, affecting crop growth and productivity worldwide. Wheat is a major cereal crop grown in various parts of the globe, which is affected severely by heat stress. The morphological parameters affected include germination, seedling establishment, source-sink activity, leaf area, shoot and root growth. The physiological parameters such as photosynthesis, respiration, leaf senescence, water and nutrient relation are also affected by heat. At the cellular level, heat stress leads to the generation of reactive oxygen species that disrupt the membrane system of thylakoid, chloroplast and plasma membrane. The deactivation of the photosystem, reduction in photosynthesis and inactivation of rubisco affect the production of photoassimilates and their allocation. This ultimately affects anthesis, grain filling, size, number and maturity of wheat grains, which hamper crop productivity. The interplay of various systems comprising antioxidants and hormones plays a crucial role in imparting heat stress tolerance in wheat. Thus, implementation of various omics technologies could foster in-depth insights on heat stress effects, eventually devising heat stress mitigation strategies by conventional and modern breeding to develop heat-tolerant wheat varieties. This review provides an integrative view of heat stress responses in wheat and also discusses approaches to develop heat-tolerant wheat varieties.

Sugarcane (Saccharum spp.) is one of the main alternatives for the bioenergy sector due to its great potential for phytomass production, being the photosynthesis a key process related to conversion of the intercepted sunlight energy into phytomass. The aim of this study was to investigate the photosynthesis of nine sugarcane varieties originated from crosses between 1948 and 2006, as well as the species Saccharum officinarum, S. spontaneum and S. robustum. In plants grown inside a growth chamber, photosynthetic response curves to increasing air CO2 concentration were performed and key photosynthetic traits and their heritabilities were estimated. Fourteen physiological traits explained ~ 95% of the variation observed. Significant differences were found in leaf CO2 assimilation at air CO2 concentration of 1500 (A1500) and 400 (A400) μmol mol−1 among sugarcane genotypes, with S. spontaneum, IAC87-3396 and RB83-5486 presenting the highest photosynthetic rates. Sugarcane photosynthesis was strongly correlated with effective quantum yield of photosystem II (r = 0.93), non-photochemical quenching (r = − 0.74), stomatal conductance (r = 0.87), in vivo maximum carboxylation rates of PEPC (Vpmax, r = 0.83) and Rubisco (Vcmax, r = 0.91) and leaf nitrogen content (r = 0.83). The heritability varied from 0.97 (leaf CO2 assimilation) to 0.84 (leaf area). The A1500:A400 ratio higher than one for all genotypes indicates that Rubisco carboxylation sites are not saturated by CO2 and a non-efficient CO2 concentration mechanism. This study revealed a significant natural genotypic variation in sugarcane photosynthesis with high heritability of important traits, suggesting the possibility of breeding for increased photosynthetic activity.

Chlamydomonas reinhardtii undergoes conditional senescence when grown in batch culture due to nutrient limitation. Here, we explored plastid and photo-physiological adaptations in Chlamydomonas reinhardtii during a long-term ageing experiment by methodically sampling them over 22 weeks. Following exponential growth, Chlamydomonas entered an extended declining growth phase where cells continued to divide, although at a lower rate. Ultimately, this ongoing division was fueled by the recycling of macromolecules that was obvious in the rapidly declining protein and chlorophyll content in the cell during this phase. This process was sufficient to maintain a high level of cell viability as the culture entered stationary phase. Beyond that the cell viability starts to plummet. During the turnover of macromolecules after exponential growth that saw RuBisCO levels drop, the LHCII antenna was relatively stable. This, along with the upregulation of the light stress-related proteins (LHCSR), contributes to an efficient energy dissipation mechanism to protect the ageing cells from photooxidative stress during the senescence process. Ultimately, viability dropped to about 7% at 22 weeks in a batch culture. We anticipate that this research will help further understand the various acclimation strategies carried out by Chlamydomonas to maximize survival under conditional senescence.

Photosynthesis is crucial to the reduction of carbon dioxide in the atmosphere. The key enzyme of photosynthesis, Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), has two mutably competing substrates, CO2 and O2. It has features of carboxylase and oxygenase. Rubisco performs the function of carboxylase to reduce inorganic carbon to form organic substances, which precondition is that more carbon dioxide accumulates around it. Carbon dioxide concentrating mechanisms (CCMs) are vital to cope with the limit of carbon dioxide. Various bicarbonate use pathway has a differential contribution to inorganic carbon assimilation. Bicarbonate transport, extracellular bicarbonate dehydration, or H+-ATPase-driven bicarbonate uptake, which induced CCMs, can support a considerable share of photosynthesis in photosynthetic organisms. However, CCMs in thylakoid membranes may be the most important. The CCMs occurred in the plasma membrane were secondary, evolutionary, and inducible, while CCMs coupled with photosynthetic oxygen evolution in thylakoid membranes, were primitive, major, and indispensable. A hypothetical schematic model of CCMs occurred in the plasma membrane and thylakoid membranes being proposed.

The cultivation of Chlorella vulgaris in sludge extract (SE) from municipal excess sludge diluted with BG11 medium was investigated to achieve sludge reduction and microalgae cultivation. A maximum biomass of 1.404 ± 0.101 g/L was achieved at 15 days in a mixture of 25% BG11 and 75% sludge extract under 10,000-lx light. In early culture periods, heterotrophy dominated the process in the group with a high proportion of sludge extract of excess sludge extract containing relatively high amounts of organic material, which led to enhanced citrate synthase enzyme activities and reduced rubisco enzyme activities. Moreover, increasing the light intensity did not significantly improve biomass production due to its inhibitory effects on respiration in the early culture stages. The response surface model showed that organic matter was the main factor influencing biomass production from 0 to 2 days. The influence of light intensity on biomass production became more noticeable only after depleting the organic matter in sludge extract.

To elucidate the mechanism of succinic acid (SA) inhibition of Microcystis aeruginosa, the chlorophyll fluorescence transients, photosynthesis, photosynthetic electron transport activity, and gene expression of M. aeruginosa were evaluated under various doses of SA. The results demonstrated that, after treatment with 60 mg L-1 SA for 1 h, the chlorophyll fluorescence transients and related parameters changed significantly, indicating that the function and structure of photosynthetic apparatuses of Microcystis were seriously damaged. The initial quantum efficiency α, maximum net photosynthetic rate Pnmax, dark respiration rate Rd, and gross photosynthetic rate decreased to 57%, 49%, 49%, and 46%, respectively, relative to the control. Furthermore, photosystem II (PSII) activity (H2O→p-BQ) and the electron transport activity of H2O→MV and DPC→MV significantly decreased. Real-time PCR analysis revealed that, following incubation with 60 mg L-1 SA for 24 h, the expression level of core protein genes (psbA, psaB, psbD, and psbO) of the photosynthesis centers photosystem I (PSI) and PSII decreased significantly. However, the transcription of gene nblA encoding phycobilisome degradation protein was elevated. The downregulation of the rbcL gene, which encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), resulted in the suppression of CO2 fixation and assimilation. High concentration (60 mg L-1) of SA resulted in damage to oxygen-evolving complex (OEC) and reaction center of PSII, blocking photosynthetic electron transport, thereby lowering the rate photosynthesis and inhibiting the growth of Microcystis. We concluded that inhibition of photosynthesis is an important mechanism of SA inhibition in M. aeruginosa.

Soil salinisation is an important factor limiting the cultivation and distribution of Prunus mume. Therefore, identifying the regulation mechanism of salt tolerance of P. mume will promote its cultivation and molecular breeding. In this study, the garden tree species P. mume ‘Meiren’ was investigated, with a soil NaCl content (w/w) of 0.3%. Photosynthetic gas exchange parameters, relative electrical conductivity, malondialdehyde, osmoregulation substances, and antioxidant enzyme activity were measured in the early (3d), middle (10d), and late (30d) stages of stress. Salt treatment was applied for 0 h, 6 h, 24 h, and 72 h; following this, the gene library was constructed from the leaves. The results showed that the CBL-CIPK, mitogen-activated protein kinase, calcium-dependent protein kinase, and abscisic acid signalling pathways were involved in salt stress signal transduction of P. mume. Furthermore, bHLH, WRPK, ERF, and MYB were identified as potential key transcription factor families of salt tolerance in P. mume. Combined with determined physiological responses, the results showed that early salt stress inhibited the activities of RuBisCO, chlorophyll synthase, glutamyl tRNA reductase, divinyl reductase, and magnesium chelatase; resultantly, this led to a reduction in the photosynthetic rate. Also, it was found that P5CS, SS, LEA, and dehydrin regulated the synthesis of proline, soluble sugar, and macromolecular protein to alleviate osmotic stress. POD gene plays an important role in scavenging reactive oxygen species due to its regulation of POD activity. The findings of this research reveal the internal mechanism of the physiological response and provide a foundation for the construction of a genetic regulatory network in response to salt stress in P. mume.

Agricultural productivity is threatened by increasing incidence of drought and the drought tolerant cyanobacteria offer a better solution in the restoration of soil fertility and productivity. The present study describes the comparative physiological response of the cyanobacterium Anabaena sp. acclimated and un-acclimated to desiccation stress induced by polyethylene glycol (10% PEG). While, the acclimated cyanobacterial cells grew luxuriantly with optimal chlorophyll content, photosynthetic activities and nitrogen fixation, the un-acclimated cells exhibited reduced growth rate, chlorophyll content, photosynthetic activities and nitrogen fixation. Distinct differences in the accumulation of lipid peroxidation products, proline and activity of superoxide dismutase were observed under identical growth conditions in the acclimated and un-acclimated cells. Desiccation-acclimated and un-acclimated cyanobacteria showed significant alterations in the abundance of important proteins in the proteome. Two-dimensional gel electrophoresis followed by MALDI-TOF-MS/MS analysis identified twelve proteins. The acclimated cells showed the up regulation of proteins such as Rubisco, fructose-bis-phosphate aldolase, fructose 1-6 bisphosphatase, phosphoglycerate dehydrogenase and elongation factors Tu and Ts as compared to un-acclimated cells. Therefore, the ability to maintain photosynthesis, antioxidants and increased accumulation of proteins related to energy metabolism helped the acclimated cyanobacterium Anabaena sp. to grow optimally under desiccation stress conditions.

This study aimed to investigate the impact of the herbicide monuron on various aspects of photosynthesis and diazotrophy in the cyanobacterium Nostoc muscorum Meg 1 isolated from a rice field in Cherrapunji, Meghalaya, India. The consequences of monuron exposure on various photosynthetic pigments, functioning of PSII, RuBisCO, nitrogenase and glutamine synthetase enzyme activities, heterocyst frequency, and on production of proteins and carbohydrates in the cyanobacterium were studied in a range of monuron doses (20–100 ppm) to gauge the herbicide’s effect on CO2 and N2 fixation and on net biomass production. The total amount of D1 protein (the host for PSII complex), RuBisCO (the key enzyme for CO2 fixation), nitrogenase (the enzyme responsible for the reduction of atmospheric nitrogen to ammonia), and ammonia assimilating enzyme glutamine synthetase (GS) contents under western blot analysis indicated interruption of new protein synthesis and breakdown of their existing enzyme molecules when exposed to higher monuron concentrations. All parameters studied showed enhanced expression under low dose monuron treatment (20 ppm) indicating a hormetic effect in the exposed organism. The expression of monuron toxicity on various parameters of CO2 and N2 fixation in a dose-dependent manner was immediately visible when cultures were treated with higher doses (40–100 ppm). Scanning and transmission electron microscopic studies further uncovered several undesirable changes in the morphology and ultrastructure of the organism due to herbicide treatment that could be correlated to compromised CO2 and N2 fixation.

Early in his career, Russ Monson produced a series of influential eco-physiological papers that helped lay the foundation for the study of C4 plant evolution. Among the most important was a 1984 paper with Maurice Ku and Gerry Edwards that outlined the pathway for the evolutionary bridge from C3 to C4 photosynthesis. This model proposed C4 photosynthesis arose out of a shuttle that imported photorespiratory metabolites into bundle sheath (BS) cells, where glycine decarboxylase cleaved off CO2, allowing it to accumulate and be efficiently refixed by BS Rubisco. By the mid-1990's, Monson's research focus had shifted away from C4 plants, save for one 2003 paper on C3 versus C4 stomatal control with Travis Huxman, and a series of critical reviews on C4 evolution. These reviews heavily influenced the modern synthesis of C4 evolutionary studies, which incorporates phylogenomic understanding with physiological, molecular, and structural characterizations of trait shifts in multiple evolutionary lineages. Subsequent research supported the Monson et al. model from 1984, by showing a glycine shuttle occurs in nearly all C3-C4 intermediate species identified. Monson also examined the physiological controls over the ecological distribution of C3, C3-C4 intermediate, and C4 photosynthesis, building our understanding of the fitness value of the intermediate and C4 pathway in relevant microenvironments. By establishing the foundation for discoveries that followed, Russ Monson can rightly be considered a leading pioneer contributing to the evolutionary biology of C4 photosynthesis.

Rising tropospheric ozone (O3) is a serious threat to plants and animals in the present climate change scenario. High tropospheric O3 has the capability to disrupt cellular organelles leading to impaired photosynthesis and significant yield reduction. Apoplast and chloroplast are two important cellular components in a plant system. Their proteomic response with ethylenediurea (EDU) treatment under tropospheric O3 has not been explored till date. EDU (an organic compound) protects plants exclusively against harmful O3 effects through activation of antioxidant defense mechanism. The present study investigated the mode of action of EDU (hereafter MAE) by identifying proteins involved in apoplast and chloroplast pathways. Two wheat varieties viz. Kundan and PBW 343 (hereafter K and P respectively) and three EDU treatments (0= control, 200, and 300 ppm) have been used for the study. In apoplast isolates, proteins such as superoxide dismutase (SOD), amino methyltransferase, catalase, and Germin-like protein have shown active role by maintaining antioxidant defense system under EDU treatment. Differential expression of these proteins leads to enhanced antioxidative defense mechanisms inside and outside the cell. Chloroplast proteins such as Rubisco, Ferredoxin NADP- reductase (FNR), fructose,1-6 bis phosphatase (FBPase), ATP synthase, vacuolar proton ATPase, and chaperonin have regulated their abundance to minimize ozone stress under EDU treatment. After analyzing apoplast and chloroplast protein abundance, we have drawn a schematic representation of the MAE working mechanism. The present study showed that plants can be capable of O3 tolerance, which could be improved by optimizing the apoplast ROS pool under EDU treatment.

Molecular evolution of the large subunit of the RuBisCO enzyme is understudied in early diverging land plants. These groups show morphological and eco-physiological adaptations to the uneven and intermittent distribution of water in the terrestrial environment. This might have prompted a continuous fine-tuning of RuBisCO under a selective pressure modifying the species-specific optima for photosynthesis in contrasting microdistributions and environmental niches. To gain a better insight into the molecular evolution of RuBisCO large subunits, the aim of this study was to assess the pattern of evolutionary change in the amino acid residues in a monophyletic group of Bryophyta (Orthotrichaceae). Tests for positive, neutral, or purifying selection at the amino acid level were assessed by comparing rates (ω) of non-synonymous (dN) and synonymous (dS) nucleotide substitutions along a Maximum Likelihood phylogenetic tree. Molecular adaptation tests using likelihood ratio tests, reconstruction of ancestral amino acid sites, and intra-protein coevolution analyses were performed. Variable amino acid sites (39) were unevenly distributed across the LSU. The residues are located on rbcL sites that are highly variable in higher plants and close to key regions implying dimer–dimer (L2L2), RuBisCO-activase interactions, and conformational functions during catalysis. Ten rbcL sites (32, 33, 91, 230, 247, 251, 255, 424, 449 and 475) have been identified by the Bayesian Empirical Bayes inference to be under positive selection and under adaptive evolution under the M8 model. The pattern of amino acid variation suggests that it is not lineage specific, but rather representative of a case of convergent evolution, suggesting recurrent changes that potentially favor the same amino acid substitutions that are likely optimized the RuBisCO activity.

Microalgae are a large group of phototrophic microorganisms that convert CO2 into biomass, which can be used as an important source of biofuels. Biofuels have a lot of interesting applications in various industries. The main objective of the current study was to assess the biomass and lipid production, gene expression of acetyl-CoA carboxylase (accD) and ribulose bisphosphate carboxylase large-chain (rbcL), and the lipid content produced by myo-inositol treatment in the microalga Chlorella vulgaris. Three different myo-inositol concentrations (i.e., 50, 100, and 200 mg/L) were added to the algal growth media, and the algal cells were sampled on the day of entering the stationary phase of the growth cycle. Biomass production was increased by increasing the supplement. However, the 200 mg/L concentration of myo-inositol was critical for lipid production. To evaluate the effect of the vitamin on the expression of the accD and rbcL genes, real-time PCR was used. The rbcL gene expression increased in relation to biomass production, i.e., 224.08 times higher than the control. On the other hand, the accD expression at 200 mg/L myo-inositol concentration, as physiological stress, increased, i.e., 95.2 times higher than the control. Therefore, this growth complement can induce biomass and lipid production. Findings of the present study provide valuable insight into determining the biochemical modulation strategies of biomass and lipid production. In this study, two separate controlling systems and two independent promoters were proposed to regulate the transcription of rbcL and accD genes induced by various concentrations of myo-inositol.

To investigate the molecular mechanism of Trichoderma L-amino acid oxidase (Th-LAAO) in protecting and in promoting growth of cabbage infected with Botrytis cinerea, a three-way interaction system was established. Cabbage leaves treated with purified Th-LAAO significantly constrained damaged leaf area caused by B. cinerea infection. In response to Th-LAAO treatment, the expression levels of genes involved in photosynthesis, such as ribulose-1,5-bisphosphate carboxylase oxygenase, Rubisco activase, and ATP synthase increased 2.54, 2.18, and 1.41 folds, respectively. The transcription levels of sucrose transport protein 1 increased 7.6 fold. As to the expression of defense-related genes, the transcription level of ascorbate peroxidase increased 1.46 fold. On the contrary, pathogenesis-related protein 1, chitinase, β-1,3 glucanase, and glutathione S-transferase decreased significantly. Overall, the results indicated that Th-LAAO may stimulate CO2 fixation and sucrose transport and elicit host defense responses in cabbage against B. cinerea, and this elicitation of defense response is likely to contribute to induced systemic resistance of host plant.

C4-like plants represent the penultimate stage of evolution from C3 to C4 plants. Although Coleataenia prionitis (formerly Panicum prionitis) has been described as a C4 plant, its leaf anatomy and gas exchange traits suggest that it may be a C4-like plant. Here, we reexamined the leaf structure and biochemical and physiological traits of photosynthesis in this grass. The large vascular bundles were surrounded by two layers of bundle sheath (BS): a colorless outer BS and a chloroplast-rich inner BS. Small vascular bundles, which generally had a single BS layer with various vascular structures, also occurred throughout the mesophyll together with BS cells not associated with vascular tissue. The mesophyll cells did not show a radial arrangement typical of Kranz anatomy. These features suggest that the leaf anatomy of C. prionitis is on the evolutionary pathway to a complete C4 Kranz type. Phosphoenolpyruvate carboxylase (PEPC) and pyruvate, Pi dikinase occurred in the mesophyll and outer BS. Glycine decarboxylase was confined to the inner BS. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) accumulated in the mesophyll and both BSs. C. prionitis had biochemical traits of NADP-malic enzyme type, whereas its gas exchange traits were close to those of C4-like intermediate plants rather than C4 plants. A gas exchange study with a PEPC inhibitor suggested that Rubisco in the mesophyll could fix atmospheric CO2. These data demonstrate that C. prionitis is not a true C4 plant but should be considered as a C4-like plant.

Mutualistic associations with symbiotic dinoflagellates (zooxanthellae) enable invertebrate hosts to thrive in tropical waters that are shallow and oligotrophic. Giant clams can harbor multiple species of symbiotic dinoflagellates (Family: Symbiodiniaceae) from mainly three genera, Symbiodinium, Cladocopium and Durusdinium, but whether they have distinct physiological functions at the genus level in the holobiont remains unclear. As symbiotic dinoflagellates use form II ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) to fix inorganic carbon, we attempted to estimate the phototrophic potentials and thus the relative abundances of Symbiodinium, Cladocopium and Durusdinium in five organs (outer mantle, inner mantle, foot muscle, ctenidium and hepatopancreas) of the fluted giant clam Tridacna squamosa through quantitative real-time PCR (qPCR) with primers that are specific to form II RuBisCO gene sequences (rbcII) of each genus. Based on the transcript levels of rbcII derived from Symbiodinium (Symb-rbcII), Cladocopium (Clad-rbcII) and Durusdinium (Duru-rbcII), we demonstrated that the symbiont population of T. squamosa from Vietnam was dominated by Durusdinium. Furthermore, the proportion of Symb-rbcII, Clad-rbcII and Duru-rbcII, and hence the phototrophic potentials of Symbiodinium, Cladocopium and Durusdinium, varied among five organs of T. squamosa, and along the length of the outer mantle. For dinoflagellates freshly isolated from the outer mantle of T. squamosa, Symb-rbcII, Clad-rbcII and Duru-rbcII exhibited different responses to light at the transcriptional level. Importantly, these results corroborate the proposition that the association with different genera and/or species of dinoflagellates might confer distinct physiological advantages to the host clam, which differs under various environmental conditions.

Rice grain yield is drastically reduced under low light especially in kharif (wet) season due to cloudy weather during most part of crop growth. Therefore, 50–60% of yield penalty was observed. To overcome this problem, identification of low light tolerant rice genotypes with a high buffering capacity trait such as photosynthetic rate has to be developed. Sedoheptulose-1,7 bisphosphatase, a light-regulated enzyme, plays pivotal role in the Calvin cycle by regenerating the substrate (RuBP) for RuBisCo and therefore, indirectly regulates the influx of CO2 for this crucial process. We found a potential role of SBPase expression and activity in low light tolerant and susceptible rice genotypes by analyzing its influence on net photosynthetic rate and biomass. We observed a significant relationship of yield with photosynthesis, SBPase expression and activity especially under low light conditions. Two tolerant and two susceptible rice genotypes were used for the present study. Tolerant genotypes exhibited significant but least reduction compared to susceptible genotypes in the expression and activity of SBPase, which was also manifested in its photosynthetic rate and finally in the grain yield under low light. However, susceptible genotypes showed significant reduction in SBPase activity along with photosynthesis and grain yield suggesting that tracking the expression and activity of SBPase could form a simple and reliable method to identify the low light tolerant rice cultivars. The data were analyzed using the Indostat 7.5, Tukey–Kramer method through Microsoft Excel 2019 and PAST4.0 software. The significant association of SBPase activity with the grain yield, net assimilation rate, electron transfer rate, biomass and grain weight were observed under low light stress. These traits should be considered while selecting and breeding for low light tolerant cultivars. Thus, SBPase plays a major role in the low light tolerance mechanism in rice.

The objective of this study was to identify the effect of abscisic acid (ABA), putrescine (Put) and hydrogen peroxide (H2O2) foliar pre-treatment on drought tolerance of barley. Despite water limitation, ABA-sprayed plants preserved increased water content, photosynthetic efficiency of PSII (ΦPSII) and CO2 assimilation rate (Pn) compared to untreated stressed plants. The ABA-treated plants presented also the lowest rate of lipid peroxidation (MDA), lowered the rate of PSII primary acceptor reduction (1 – qP) and increased the yield of regulated energy dissipation (NPQ) with higher accumulation of PGRL1 (PROTON GRADIENT REGULATION LIKE1) protein. These plants preserved a similar level of photochemical efficiency and the rate of electron transport of PSII (ETRII) to the well-watered samples. The significantly less pronounced response was observed in Put-sprayed samples under drought. Additionally, the combined effects of drought and H2O2 application increased the 1 – qP and quantum yield of non-regulated energy dissipation in PSII (ΦNO) and reduced the accumulation of Rubisco activase (RCA). In conclusion, ABA foliar application allowed to balance water retention and preserve antioxidant capacity resulting in efficient photosynthesis and the restricted risk of oxidative damage under drought. Neither hydrogen peroxide nor putrescine has been able to ameliorate drought stress as effectively as ABA.

Made available in DSpace on 2022-05-01T16:48:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-04-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In tropical no-till systems, applying lime (L) and phosphogypsum (PG) on the soil surface may be a potential strategy for reducing soil acidification and improving soybean root growth, thereby enhancing plant nutrition and physiological responses and, in turn, crop resistance to dry spells. This study evaluated the impact of long-term (17 years) surface soil amendment on soil fertility and soybean root development, nutrition, gas exchange, carbon and antioxidant enzyme activity, and grain yield in a tropical region subject to dry spells. The treatments consisted of the following long-term soil amendments: control (no soil amendment); L alone; PG alone; and L + PG (LPG). Liming, especially when combined with PG, improved soil fertility, as evidenced by increases in pH and P, Ca2+, and Mg2+ levels throughout the soil profile, but reduced Al3+ and micronutrients (Fe, Mn, Cu, and Zn). The improvements in soil fertility were associated with increased root development throughout the profile. Long-term application of LPG reduced the negative impacts of dry spells on pigment concentrations, gas exchange, Rubisco and sucrose synthase activities and antioxidant metabolism, and increased soybean grain yield. Our results reveal that long-term application of LPG is an important approach for increasing the vertical movement of cationic bases and roots in no-till systems to improve soybean nutrition. Long-term amendment with LPG enhanced both carbon and antioxidant metabolism in soybean plants, resulting in higher soybean grain yield, despite the predisposition of this tropical region to dry spells. Department of Crop Science College of Agricultural Sciences São Paulo State University (UNESP), São Paulo Department of Soil Science and Agricultural Engineering State University of Ponta Grossa (UEPG), Paraná Soils Department Center of Rural Sciences (CRS) Federal University of Santa Maria (UFSM), Rio Grande do Sul Department of Biosystems Engineering School of Sciences and Engineering São Paulo State University (UNESP), São Paulo Department of Crop Science College of Agricultural Sciences São Paulo State University (UNESP), São Paulo Department of Biosystems Engineering School of Sciences and Engineering São Paulo State University (UNESP), São Paulo FAPESP: 2018/11063-7 FAPESP: 2019/12764-1 CNPq: 421637/2018-8

The review describes the structures of plant carbonic anhydrases (CAs), enzymes catalyzing the interconversion of inorganic carbon forms and belonging to different families, as well as the interaction of inhibitors and activators of CA activity with the active sites of CAs in representatives of these families. We outline the data that shed light on the location of CAs in green cells of C3 plants, algae and angiosperms, with the emphasis on the recently obtained data. The proven and proposed functions of CAs in these organisms are listed. The possibility of the involvement of several chloroplast CAs in acceleration of the conversion of bicarbonate to CO2 and in supply of CO2 for fixation by Rubisco is particularly considered. Special attention is paid to CAs in various parts of thylakoids and to discussion about current knowledge of their possible physiological roles. The review states that, despite the significant progress in application of the mutants with suppressed CAs synthesis, the approach based on the use of the inhibitors of CA activity in some cases remains quite effective. Combination of these two approaches, namely determining the effect of CA activity inhibitors in plants with certain knocked-out CA genes, turns out to be very useful for understanding the functions of other CAs.

The present study was carried out to investigate the effects of hydrogen peroxide (H2O2) on the growth, photosynthesis, leaf histology, mineral uptake, phytochemical accumulation, and Rubisco gene expression in Ficus deltoidea var. deltoidea, a slow growing medicinal plant. The F. deltoidea plants were spray-treated with 0 (control), 8, 16, 30 and 60 mM H2O2 under field conditions. The results showed that the applications of 30 mM H2O2 increased the plant height, leaf number, and syconium number by 26%, 9% and 2275%, respectively, over the control specimen. Photosynthetic rates, transpiration, stomatal conductance and chlorophyll content of F. deltoidae plants increased significantly after treatment of 30 mM H2O2. A lower concentration (8 and 16 mM) of H2O2 also improved the leaf histological properties such as tracheary elements and other vascular cells. In addition, treatments with 30 mM H2O2 increased calcium, potassium, total phenolic and flavonoids content, in F. deltoidea plants, by 14%, 15%, 12% and 72%, respectively. In addition, H2O2 treatment at 30 mM concentration downregulated the Rubisco gene with a between 1 and 5 times fold gene expression change. From this study, it can be concluded that spraying with 30 and 16 mM of H2O2 once a week enhanced growth, photosynthesis, mineral accumulation, phenol and flavonoid content, as well as aided Rubisco gene expression, under field conditions.

The present study was aimed to assess the effect of nitric oxide (NO) and the interaction of NO with hydrogen peroxide (H2O2) on plant tolerance to low temperatures in cucumber seedlings. Exogenous NO significantly increased the endogenous NO content, initial and total activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), RuBisCO carboxylation rate (Vc,max), RuBP regeneration rate (Jmax) and the transcript levels of related genes in cucumber seedlings under low temperatures (11 °C/7 °C); however, the effect of NO was blocked by PTIO (NO scavenger). In addition, the SNP treatment significantly improved the contents of glucose, fructose, sucrose, starch, and the activities of sucrose phosphate synthase (SPS), acid invertase (AI), sucrose synthase (SS), as well as the expression levels of SUCROSE PHOSPHATE SYNTHASE 1&2 (SPS1, SPS2), SUCROSE TRANSPORTER 1&2 (SUT2, SUT4), β-starch hydrolase (BAM), and invertase gene (INVERTASE) in cucumber leaves under low temperatures, and the positive effect of NO was impaired by PTIO. Furthermore, we found that the H2O2, induced by NO, participated in NO-induced elevation of ascorbic acid (AsA), glutathione (GSH), and increased activities of related enzymes in the AsA-GSH cycle at low temperatures. However, the positive effect of NO was blocked by l-NAME (NOS inhibitor), PTIO, DPI (inhibitor of NADPH oxidase), and DMTU (reactive oxygen species scavenger). Taken together, our findings indicate that NO increased the low temperature tolerance of cucumber seedlings via H2O2 by improving the efficiency of the Calvin cycle, which in turn increased the carbohydrates content and accelerated the AsA-GSH cycle to enhance ROS scavenging.

Role of Rubisco Activase in imparting thermotolerance to the photosynthetic apparatus under high temperature. Thus, to improve the grain filling, we need to fine tune these crucial enzymes and their regulation, which directly or indirectly affect spike photosynthesis. CO2 fixation in cereals crops like bread wheat (Triticum aestivum L.) is also contributed by ear photosynthesis beside the other organs like leaves or the flag leaf. 1000-grain weight of three Indian wheat cultivars (cvs.) PBW343, K7903, and HD2329 were calculated under three treatments until maturity stage (i.e. removal of flag leaf, removal of awns and shaded spikes). We observed that awn removal showed a significant decrease in 1000-grain weight in all cultivars. To delve deeper into the biological and molecular pathways taking place underlying the awn physiology, we conducted the awn transcriptome analysis of thermosusceptible Indian wheat cv. PBW343 under heat stress (HS) at 42 °C for 2 h using RNA-sequencing (RNA-seq). Differential expression analysis revealed, 160 transcripts, out of these, 143 transcripts were significantly upregulated and 17 transcripts were repressed under HS conditions. Of these Rca1β was selected for characterization and overexpression studies. Ectopic expression of TaRca1β in rice transgenics indicate a direct correlation with tolerance under HS conditions. TaRca1β provides a better photosynthate energy partitioning under HS with a significant reduction in the non-photochemical fluorescence quenching of the photosynthetic machinery.

The algal pyrenoid is a naked phase-separated liquid compartment inside the chloroplast consisting predominantly of densely packaged Rubisco and most often transversed by a system of lipid membranes. The pyrenoid participates in carbon-concentrating mechanisms of algae. During the cell division, the daughter cells of algae acquire the pyrenoids via their assembly or fission, the mechanisms of which are not fully understood. We suppose that the chloroplast nucleoid scaffolds the new pyrenoid like the cyanobacterial nucleoid positions carboxysomes before the cell division. This work was aimed at visualization and localization of the chloroplast DNA relative to the pyrenoid in synchronously dividing cells of Dunaliella salina with DNA-specific fluorescent DAPI stain through the fluorescent confocal microscope. The intense DNA-specific blue DAPI fluorescence was discovered in the pyrenoids matrix under the starch shell in the presumably pre-mitotic cells, during and following the pyrenoid fission. In the interphase cells, the chloroplast DNA localized both in the pyrenoid core and in several small nucleoids on the outer surface of the starch shell around the pyrenoid. The observations were compared with the literature data on the same and other algal species. The spatial pre-requisite exists in D. salina for the chloroplast nucleoid to scaffold the pyrenoid fission. A potential alternative explanation was declared being the algal pyrenoid as the chloroplast genetic center. The theoretical and practical implications of the findings were discussed.

Chlorella vulgaris is a form of microalgae commonly employed as a biological source of oil for biodiesel production. Major algal cultivation strategies are focused on stimulating growth rate and lipid content. In the present study, the algal growth media was supplemented with iron (III) chloride (FeCl3), as a stimulating factor for growth and lipid production, in three iron concentrations including 90, 200, and 500 µM. The turbidity of algal cells was measured on different days, to determine the growth rate. In optimum iron concentration, this measurement experienced a 2.1-fold increase. Next, the lipid content was extracted, and the amount of lipid produced in each treatment was calculated, which demonstrated a 4.57-fold increase in lipid productivity. The expression of genes corresponding to the metabolic enzymes (i.e. acetyl-CoA carboxylase (accD) and ribulose bisphosphate carboxylase large chain (rbcL)) was evaluated using real-time PCR under different initial iron feeds. As demonstrated in the results, the initial iron feed of 90 µM was an optimum concentration that obtained the highest growth rate, more cell density, and increased lipid production. In 90 µM initial iron concentration, the expression of accD and rbcL genes showed a 4.8- and 35-fold increase, respectively, compared to that of the control genes. Based on the results, this optimum iron concentration could satisfy the industrial interest in biodiesel production from C. vulgaris as a potential stimulating factor. However, higher levels of iron (e.g. 200 and 500 µM) failed to act as positive stress for increasing biodiesel production. Finally, in this paper, different mechanisms where iron affects acetyl-CoA carboxylase (ACCase) and 1,5-ribulose bisphosphate carboxylase/oxygenase (RuBisCo) are illustrated.

Nitric oxide (NO) acts as a gaseous diffusible plant growth regulator. It plays an important role in growth and development of plants. Therefore, in present study mustard plants were sprayed with different concentrations of sodium nitroprusside (0, 10–4 M, 10–5 M and 10–6 M), a donor of NO, at 25 days after sowing to assess different physiological parameters. The results indicate that foliar spray of SNP upregulate chlorophyll content, chlorophyll fluorescence along with gaseous exchange parameters which further boost overall photosynthetic efficiency. A gradual increase in carbon metabolism (total reducing sugars, total carbohydrate content, glucose, fructose, sucrose and starch content) was also observed in SNP-treated plants as compared to control. Nutrient status (carbon, nitrogen, phosphorus, sulfur, potassium and magnesium) of leaves also shows a significant increase. The activity of various enzymes associated with nitrogen metabolism, CO2/HCO3− homeostasis, glycolysis, Calvin cycle and Krebs cycle (nitrate reductase, carbonic anhydrase, hexokinase, rubisco, fumarase and succinate dehydrogenase) were also increased in the presence of SNP. It was also reported that O2−, H2O2 and MDA were decreased in SNP-treated samples. SNP application also upregulate antioxidative defense system by increasing the activity of antioxidant enzymes, i.e., CAT, POX and SOD. Thus, it can be concluded from the present observation that SNP proved beneficial and alter most of the parameters which ultimately improve photosynthetic efficiency in mustard plants.

Phosphorus (P) is an essential macronutrient for plant growth and its metabolism. Because reproductive growth could be influenced by carbon metabolism of the functional leaf (MSL), we hypothesized that soil available phosphorus (AP) deficiency would limit boll dry mass distributions of the whole cotton plant by decreasing photosynthesis of MSL and inhibiting carbon metabolism in the MSL. This study aimed to determine the correlations between carbon metabolism and cotton boll dry mass in relation to soil AP deficiency, and key carbon-metabolism enzymes responsive to P for different low-P-sensitive cultivars. A three-year (2015–2017) pot experiment was conducted with three available phosphorus (AP) levels [3 (P0, AP deficiency), 8 (P1), and 12 (P2, as a control) mg P2O5 kg−1] with two cotton cultivars (CCRI 79 and LMY 28). Low soil AP had significant decreases on leaf P content, net photosynthetic rate (Pn) in the functional leaf (MSL), as well as boll dry mass. The P0 and P1 caused a significant increase in nonstructural carbohydrates (soluble sugar, sucrose, hexose, starch), in especial sucrose (↑8–17% for CCRI 79 and ↑20–32% for LMY 28). Similarly, the lower P levels (P0 and P1) prominently down-regulated the activities of Rubisco, sucrose phosphate synthase (SPS), and amylase, but up-regulated cytosolic fructose-1,6-bisphosphatases and soluble acid invertase (SAI). Moreover, only the absolute value of slope in SAI for LMY 28 was higher than that for CCRI 79 in 2015 and 2016. Our results indicated that the response of carbon-metabolizing enzymes to low AP content was mediated by SAI for CCRI 79 and LMY 28. In our results, Pn, Rubisco, and SAI were the dominant factors affecting the boll dry mass under low soil AP.

The folding and assembly of RuBisCO, the most abundant enzyme in nature, needs a series of chaperones, including the RuBisCO accumulation factor Raf1, which is highly conserved in cyanobacteria and plants. Here, we report the crystal structures of Raf1 from cyanobacteria Anabaena sp. PCC 7120 and its complex with RuBisCO large subunit RbcL. Structural analyses and biochemical assays reveal that each Raf1 dimer captures an RbcL dimer, with the C-terminal tail inserting into the catalytic pocket, and further mediates the assembly of RbcL dimers to form the octameric core of RuBisCO. Furthermore, the cryo-electron microscopy structures of the RbcL-Raf1-RbcS assembly intermediates enable us to see a dynamic assembly process from RbcL8Raf18 to the holoenzyme RbcL8RbcS8. In vitro assays also indicate that Raf1 can attenuate and reverse CcmM-mediated cyanobacterial RuBisCO condensation. Combined with previous findings, we propose a putative model for the assembly of cyanobacterial RuBisCO coordinated by the chaperone Raf1.

Thaumarchaeota constitute an abundant and ubiquitous phylum of Archaea that play critical roles in the global nitrogen and carbon cycles. Most well-characterized members of the phylum are chemolithoautotrophic ammonia-oxidizing archaea (AOA), which comprise up to 5 and 20% of the total single-celled life in soil and marine systems, respectively. Using two high-quality metagenome-assembled genomes (MAGs), here we describe a divergent marine thaumarchaeal clade that is devoid of the ammonia-oxidation machinery and the AOA-specific carbon-fixation pathway. Phylogenomic analyses placed these genomes within the uncultivated and largely understudied marine pSL12-like thaumarchaeal clade. The predominant mode of nutrient acquisition appears to be aerobic heterotrophy, evidenced by the presence of respiratory complexes and various organic carbon degradation pathways. Both genomes encoded several pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenases, as well as a form III RuBisCO. Metabolic reconstructions suggest anaplerotic CO(2) assimilation mediated by RuBisCO, which may be linked to the central carbon metabolism. We conclude that these genomes represent a hitherto unrecognized evolutionary link between predominantly anaerobic basal thaumarchaeal lineages and mesophilic marine AOA, with important implications for diversification within the phylum Thaumarchaeota.

Pyropia haitanensis has a typical parthenogenetic behavior under unisexual culture condition. In this study, ultrastructural evolution and physiological traits of photosynthesis and the expression characteristics of key enzyme genes related to carbon and nitrogen assimilation pathways at different developmental stages of parthenogenesis were analyzed. Ultrastructural observations showed that the gametophytic vegetative cells had cell wall, pyrenoids, abundant chloroplasts, and rarely scattered floridean starch grains. However, the appearance of gathered chloroplasts, plastoglobuli, large lipid droplets, pyrenoids encircled by numerous plastoglobuli, and an increased number of floridean starch grains in the cells during parthenogenesis provide neutral lipid and energy resources that are compatible with the developmental transitions. Physiologically, vegetative gametophytes possessed the highest Fv/Fm and Chl. a content and the lowest C/N ratio. However, compared with vegetative cell proliferation stage, the activities of RubisCO (ribulose bisphosphate carboxylase) and external CA (carbonic anhydrase) increased at early stages of parthenogenesis, and Fv/Fm and activities of PEPC (phosphoenolpyruvate carboxylase) and PEPCK (phosphoenolpyruvate carboxykinase) remained higher at later stages of parthenogenesis, suggesting that dynamic photosynthetic carbon fixation occurs in parthenogenesis. Quantitative real-time PCR analysis showed that selective regulation of key enzyme genes related to carbon and nitrogen assimilation pathways maintained stable carbon and nitrogen metabolism during developmental transitions of parthenogenesis. Moreover, during parthenogenesis, photosynthetic carbon fixation pathway potentially changed from C3 pathway at female gametophyte stage to C4 pathway at parthenosporophyte stage, which is similar to that of gametophytes and sporophytes in sexual reproduction. Meanwhile, the ammonia assimilation involved GDH pathway (glutamate dehydrogenase pathway) and GS/GOGAT cycle (glutamine synthetase/glutamate synthase cycle) in female gametophyte stage, while GS/GOGAT cycle was dominant in parthenosporophyte stage, suggesting that GS/GOGAT cycle may play an important role in the carbon and nitrogen balance during the developmental transitions of parthenogenesis. These results provide important information for revealing the adaptation strategy of parthenogenesis in Pyropia.

Inhibition of angiotensin I-converting enzyme (ACE) is one of the key factors to repress high blood pressure. Although many studies have been reported that seaweed protein hydrolysates showed the ACE inhibitory activity, the comprehensive understanding of the relationship was still unclear. In this study, we employed chloroplast genome for in silico analysis and compared it with in vitro experiments. We first extracted water-soluble proteins (WSP) from red alga Grateloupia asiatica, which contained mainly PE, PC, APC, and Rbc, and prepared WSP hydrolysate by thermolysin, resulting that the hydrolysate showed ACE inhibitory activity. Then, we determined the complete chloroplast genome of G. asiatica (187,518 bp: 206 protein-coding genes, 29 tRNA, and 3 rRNA) and clarified the amino acid sequences of main WSP, i.e., phycobiliproteins and Rubisco, to perform in silico analysis. Consequently, 190 potential ACE inhibitory peptides existed in the main WSP sequences, and 21 peptides were obtained by in silico thermolysin digestion. By comparing in vitro and in silico analyses, in vitro ACE inhibitory activity was correlated to the IC50 value from in silico digestion. Therefore, in silico approach provides insight into the comprehensive understanding of the potential bioactive peptides from seaweed proteins.

A green-colored gametophytic blade of wild Pyropia was found in a natural population in the estuary area of the Naruse River, northeast Japan. To identify the isolated green mutant strain K-G1 and the wild-type strain K-1 derived from the same population, we carried out morphological observations and molecular analysis of the RUBISCO spacer region and the rbcL gene. As a result, the two strains were identified as Pyropia kinositae, which is a species closely related to the marine crop Pyropia yezoensis. Under the same laboratory culture, the growth and pigment contents of the green mutant K-G1 were compared with those of the wild-type K-1. The growth of the conchocelis and gametophytic blade tended to be slower in the green mutant than in the wild type, although differences in their growth were not apparent in some of the temperature conditions examined. Maturation of the conchocelis and blade in the two strains was fastest at 20 °C among the temperature conditions examined (5–25 °C). The phycoerythrin content was significantly lower in the green mutant than in the wild type. Additionally, the color phenotype of the green mutant was genetically stable in both the sporophytic conchocelis and gametophytic phases. Because the color of a pigmentation mutant facilitates cross-confirmation as a genetic marker in monoecious Pyropia species, these results suggest that the green mutant of P. kinositae will contribute as new breeding material for cross-breeding and polyploidy breeding in Pyropia.

The green revolution’s breeding of semi-dwarf rice cultivars in the 1960s improved crop yields, with large increases in the use of nitrogen (N) fertilizer. However, excess N application has caused serious environmental problems, including acid rain and the eutrophication of rivers and oceans. To use N to improve crop yields, while minimizing the associated environmental costs, there is a need to produce crops with higher N-use efficiency and higher yield components. Here we show that transgenic rice overproducing ribulose 1,5-bisphosphate carboxylase–oxygenase (Rubisco)—the key enzyme of photosynthesis—exhibits increased yields with improved N-use efficiency for increasing biomass production when receiving sufficient N fertilization in an experimental paddy field. This field experiment demonstrates an improvement in photosynthesis linked to yield increase due to a higher N-use efficiency in a major crop. Transgenic rice engineered to increase photosynthetic activity through overproduction of ribulose 1,5-bisphosphate carboxylase–oxygenase (Rubisco) shows increased rice yields, with improved nitrogen-use efficiency, in an experimental paddy field.

Rubisco specificity factor (Sc/o), a measure of the relative capacities of an enzyme to catalyze carboxylation and oxygenation of ribulose-1,5-bisphosphate, determines the extent of photosynthetic CO2 assimilation and photorespiratory CO2 release. The current model of C3 photosynthesis, the Farquhar–von Caemmerer–Berry (FvCB) model, requires a species-specific Sc/o. However, Sc/o values have never been reported in conifers, likely because in vitro kinetic analysis of conifer Rubisco presents difficulties. To estimate the Sc/o of conifers and compare it with angiosperm Sc/o, we measured changes in leaf CO2 compensation points (Γ) in response to O2 partial pressure for a variety of leaves, with different rates of day respiration (Rday) and maximum Rubisco carboxylation (Vcmax) in gymnosperms (Ginkgo biloba), conifers (Metasequoia glyptostroboides and Cryptomeria japonica), and angiosperms (Nicotiana tabacum and Phaseolus vulgaris). As predicted by the FvCB model, the slope of a linear function of Γ vs O2 partial pressure, d, increased alongside increasing Rday/Vcmax. The Sc/o was obtainable from this relationship between d and Rday/Vcmax, because the d values at Rday/Vcmax = 0 corresponded to α/Sc/o, where α was the photorespiratory CO2 release rate per Rubisco oxygenation rate (generally assumed to be 0.5). The calculated Sc/o values of N. tabacum and P. vulgaris exhibited good agreement with those reported by in vitro studies. The Sc/o values of both conifers were similar to those of the two angiosperm species. In contrast, the Sc/o value of G. biloba was significantly lower than those of the other four studied species. These results suggest that our new method for Sc/o estimation is applicable to C3 plants, including those for which in vitro kinetic analysis is difficult. Furthermore, results also suggest that conifer Sc/o does not differ significantly from that of C3 angiosperms, assuming α remains unchanged.

Grapevine is one of the most important fruit crops in the world, which is severely threatened by drought. Therefore, understanding grapevine drought response mechanisms is needed to develop grapevine cultivars that can tolerate this stress. In the present report, a comparative proteomic study using 2D-PAGE was performed on two wild grapevine accessions, Tebaba (salt tolerant) and Houamdia (salt sensitive), to identify proteins that play key roles in drought responsive mechanisms. Plants were exposed to water deficit stress for 16 days. Physiological observations did not indicate any difference in drought tolerance between the two accessions. However, the comparative proteomic study showed that 18 drought-responsive proteins changed in both accessions under drought stress and 48 (29 in Houamdia and 19 in Tebaba) were variety specific. Based on changes in protein abundance induced by drought stress, carbohydrate and energy metabolism were similarly up-regulated in both accessions. Amino acid metabolism was more negatively affected by the stress in Houamdia accession. Interestingly, the three ROS scavenging proteins APX, ASR2 and GRXS17 were up-regulated only in Tebaba. Some drought-responsive proteins, such as RBP, RuBisCO, RCA, 26S protease, CLpA and 14–3-3-like protein were up-regulated by the stress in Tebaba, whereas they were down-regulated in Houamdia. Taken together, these results suggest that Tebaba may alleviate drought stress through an activation of photosynthesis and redox reactions, and a degradation of misfolded/damaged proteins. Information given in this report could be helpful for selecting candidate proteins/genes as markers in improving drought tolerance in grapevine cultivars.

Despite living in oligotrophic tropical waters, giant clams can grow to large sizes because they live in symbiosis with extracellular phototrophic dinoflagellates (zooxanthellae) and receive photosynthates from them. The physical presence of zooxanthellae in five organs (colorful outer mantle, whitish inner mantle, ctenidium, hepatopancreas and foot muscle) of Tridacna squamosa had been confirmed by microscopy, and high densities of zooxanthellae were detected in specific regions of the inner mantle and foot muscle. Symbiotic dinoflagellates use form II ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) to fix inorganic carbon during C3 photosynthesis. Using qPCR primers that were designed comprehensively against all known zooxanthellal form II RuBisCO gene sequences (rbcII) in existing databases, we demonstrated that the outer mantle of T. squamosa (TS) had the greatest phototrophic potential as reflected by its high zooxanthellal rbcII (TSZrbcII) transcript level, which varied among different regions of the outer mantle. The other four organs also expressed moderate levels of TSZrbcII, despite the lack of iridophores and direct light exposure. Importantly, light exposure led to significant increases in the protein abundance of TSZRBCII in the outer mantle but not the other four organs. Taken together, these results indicate that organs inside the mantle cavity had low phototrophic potentials, but zooxanthellae residing inside these organs might serve some unidentified functions to benefit the host.

Sugarcane mosaic virus (SCMV), belonging to genus Potyvirus, family Potyviridae, is a severe pathogen of several agricultural important crops, mainly sugarcane. Due to complex nature of sugarcane, the effect of SCMV pathogenicity on sugarcane photosynthetic systems remains to be explored. In this study, we investigated the alterations occurring in the photosynthetic system in the sugarcane genotypes at the cytopathological, physiological and biological, transcriptome and proteome level. We generated the transcriptome assembly of two genotypes (susceptible Badila and resistant B-48) using Saccharum spontaneum L. as a reference genome. RNA-sequencing data revealed the significant upregulation of NAD(P)H, RubisCO, oxygen-evolving complex, chlorophyll a and b binding protein, Psb protein family, PSI reaction center subunit II, and IVgenes in B-48, as compared to its counterparts. Upregulated genes in B-48 are associated with various processes such as stability and assembly of photosystem, protection against photoinhibition and antiviral defense. The expression pattern of differentially abundant genes were further verified at the proteomics level. Overall, differentially expressed genes/proteins (DEGs/DEPs) showed the consistency of expression at both transcriptome and proteome level in B-48 genotype. Comprehensively, these data supported the efficiency of B-48 genotype under virus infection conditions and provided a better understanding of the expression pattern of photosynthesis-related genes in sugarcane.

Photosynthesis could be improved by increasing photosynthetic rate per unit leaf area and by optimizing light interception and utilization through modified canopy architecture, and also by modifying photosynthetic duration. The yield potential of wheat is determined by the accumulated photosynthates over the entire growing season or the fraction of the total biomass partitioned into grain at harvest. Significant correlation between grain yield and net photosynthesis rate was found under controlled environmental condition (in vitro) but similar relationship under open field conditions is not established. However, phenotyping of photosynthetic traits based on biochemical models can provide accurate physiological information, and thus connecting those traits with yield at crop level would only make crop improvement feasible involving photosynthetic manipulations. At this perspective, the present investigation was undertaken with ten diverse wheat genotypes to characterize pre-anthesis photosynthetic traits and its possible relationship with wheat productivity under in vivo condition. Genotypes were found to have high natural variations for pre-anthesis photosynthetic traits under in vivo condition. Genotypes like DPW-621-50, K 0307, HW 2044 were having high value of Vcmax, Jmax and Cc and thus expected to have better photosynthetic efficiency under ambient atmospheric CO2 condition. Rubisco specificity factor (τ) was found high in KRL-210, HD 2009, KRL-19 and thus expected to have better carboxylase activity under normal condition. Maximum genetic distance was recorded between KRL-210 and DPW-621-50. Rubisco specificity factor (τ) was found as highly correlated with fraction of photorespiration (F) and chloroplast CO2 concentration (Cc). Positive correlation of Cc with fraction of photorespiration (F), mesophyll conductance (gm) and Rubisco specificity factor (τ) indicated high value of CO2 compensation point (Г*). However, correlation between flag leaf photosynthesis rate and grain or biological yield was found non-significant in the present wheat genotypes.

24-Epibrassinolide (EBL) and/or spermine (Spm) applications regulate photosynthetic process and hormonal balance in drought-stressed plants. A pot experiment was conducted to investigate the potential effects of 25 mg l−1 EBL and/or 0.1 mg l−1 Spm applied to maize (Zea mays L.; hybrid Giza 129) exposed to water deficiency (50 and 75% field capacity). Plastic pots were planted with maize plants and designed in a complete randomized design with four replications. Drought significantly impaired photosynthetic pigments content, photochemical reactions of photosynthesis, net photosynthetic rate, transpiration rate, stomatal conductance, maximum quantum efficiency of PSII photochemistry, electron transport rate, actual photochemical efficiency of PSII, photochemical quenching coefficient, effective quantum yield of PSII photochemistry, activities of Rubisco, Rubisco activase, and carbonic anhydrase, seeds carbohydrate content as well as concentrations of auxins, cytokinins, and gibberellins. These changes were significantly modulated in drought-affected plants after EBL and Spm combined application. Moreover, this combined treatment under water shortage conditions inhibited the increased concentrations of intercellular CO2, non-photochemical quenching coefficients, and abscisic acid as well as diminished the enhanced activity of glycolate oxidase. These results reinforce the utility of this combined treatment not only in improving the photosynthetic capability but also in regulating the hormonal homeostasis as a powerful strategy to enhance the plant drought tolerance. Indeed, exogenous application of 25 mg l−1 Spm + 0.1 mg l−1 EBL can preserve the photosynthetic apparatus activity under water deficiency.

Purple non-sulfur photosynthetic bacteria such as Rhodobacter sphaeroides and Rhodopseudomonas palustris produce hydrogen gas (H2) via proton reduction, which is catalyzed by nitrogenase. Although the expression of nitrogenase is usually repressed under nitrogen-sufficient conditions, a partial deletion of nifA, which encodes a transcriptional activator of nitrogen-fixation genes, has been reported to enable the constitutive expression of nitrogenase in R. palustris. In this study, we evaluated the effects of a similar mutation (nifA* mutation) on H2 production during the photoheterotrophic growth of R. sphaeroides, based on the notion that H2 production by nitrogenase compensates for the loss of CO2 fixation via the Calvin cycle, thereby restoring the redox balance. The chromosomal nifA* mutation resulted in the slight restoration of the photoheterotrophic growth of a mutant strain lacking ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), the key enzyme of the Calvin cycle, when the strain was cultured in van Niel's yeast medium. In addition, the strain with the nifA* mutation produced detectable levels of H2 during photoheterotrophic growth with acetate and ammonium; however, the H2 production was considerably lower than that observed during the photoheterotrophic growth of the strain with acetate and L-glutamate, where L-glutamate serves as a poor nitrogen source, thereby causing nitrogenase derepression. On the other hand, introduction of a multicopy plasmid harboring nifA* markedly restored the photoheterotrophic growth of the RubisCO-deletion mutant in van Niel's yeast medium and resulted in efficient H2 production during the photoheterotrophic growth with acetate and ammonium.

The oxygenase activity of Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) converts ribulose-1,5-bisphosphate (RuBP) into 2-phosphoglycolate, which in turn channels into photorespiration, resulting in carbon and energy loss in higher plants. We observed that glycolate can be accumulated extracellularly when two genes encoding the glycolate dehydrogenase of cyanobacteria Synechocystis sp. PCC 6803 were inactivated. This inspired us to explore the oxygenase function of Rubisco for production of glycolate, an important industrial chemical, from CO

With the rapid growth of world population, it is essential to increase agricultural productivity to feed the growing population. Over the past decades, many methods have been used to increase crop yields. Despite the success in boosting the crop yield through these methods, global food production still needs to be increased to be on par with the increasing population and its dynamic consumption patterns. Additionally, given the prevailing environmental conditions pertaining to the global temperature increase, heat stress will likely be a critical factor that negatively affects plant biomass and crop yield. One of the key elements hindering photosynthesis and plant productivity under heat stress is the thermo-sensitivity of the Rubisco activase (RCA), a molecular chaperone that converts Rubisco back to active form after it becomes inactive. It would be an attractive and practical strategy to maintain photosynthetic activity under elevated temperatures by enhancing the thermo-stability of RCA. In this context, this review discusses the need to improve the thermo-tolerance of RCA under current climatic conditions and to further study RCA structure and regulation, and its limitations at elevated temperatures. This review summarizes successful results and provides a perspective on RCA research and its implication in improving crop yield under elevated temperature conditions in the future.

Hypergravity—an evolutionarily novel environment has been exploited to comprehend the response of living organisms including plants in the context of extra-terrestrial applications. Recently, researchers have shown that hypergravity induces desired phenotypic variability in seedlings. In the present study, we tested the utility of hypergravity as a novel tool in inducing reliable phenotype/s for potential terrestrial crop improvement applications. To investigate, bread wheat seeds (UAS-375 genotype) were subjected to hypergravity treatment (10×g for 12, and 24 h), and evaluated for seedling vigor and plant growth parameters in both laboratory and greenhouse conditions. It was also attempted to elucidate the associated biochemical and hormonal changes at different stages of vegetative growth. Resultant data revealed that hypergravity treatment (10×g for 12 h) significantly enhanced root length, root volume, and root biomass in response to hypergravity. The robust seedling growth phenotype may be attributed to increased alpha-amylase and TDH enzyme activities observed in seeds treated with hypergravity. Elevated total chlorophyll content and Rubisco (55 kDa) protein expression across different stages of vegetative growth in response to hypergravity may impart physiological benefits to wheat growth. Further, hypergravity elicited robust endogenous phytohormones dynamics in root signifying altered phenotype/s. Collectively, this study for the first time describes the utility of hypergravity as a novel tool in inducing reliable root phenotype that could be potentially exploited for improving wheat varieties for better water usage management.

RuBisCO (Ribulose 1,5 bisphosphate carboxylase/oxygenase) by virtue of its dual specificity towards oxygen and carbon dioxide is an important rate-limiting step in photosynthesis and is believed to be the key factor for limited productivity of higher plants and algae. The photoautotrophic growth rate of cyanobacteria is a culmination of several factors including, rates of photosynthetic reactions, stress combating mechanisms and basic biomass generation metabolism in combination with optimal nutrient availability, irradiance, gaseous environment, etc. In case of cyanobacteria, the effect of RuBisCO in affecting the multiplication rate has been observed to show varied response. The current paper presents the RuBisCO activity of an early diverging cyanobacterium, Gloeobacter violaceus PCC 7421 and also compares the growth rates and RuBisCO activity of various cyanobacteria. A spectrophotometric estimation in a coupled enzyme assay system of the heterologous expressed G. violaceus PCC 7421 RuBisCO in E. coli, upon purification, revealed a carboxylation activity of LSu to be 5 nMol of phosphoglycerate min-1 mg-1 of protein, which is in coherence with the organism's slow growth rate. Further, the in vitro complementation of RbcL with RbcS in presence of RbcX of G. violaceus facilitated partial reconstitution of the protein and was hence found to cause a four-fold enhancement in its specific activity. The unique characteristics of the primitive cyanobacteria, such as, absence of thylakoids, lack of several photosystem constituting genes, slow carboxylation rate, pose limitation for its rapid multiplication. The RuBisCO carboxylation rate is observed as not the sole but an important parameter for obtaining optimal cell multiplication rates in photo-autotrophically multiplying cyanobacteria.

G protein γ subunit qPE9-1 plays multiple roles in rice growth and development. However, the role of qPE9-1 in rice exposed to elevated carbon dioxide concentration (eCO2) is unknown. Here, we investigated its role in the regulation of rice growth under eCO2 conditions using qPE9-1 overexpression (OE) lines, RNAi lines and corresponding WT rice. Compared to atmospheric carbon dioxide concentration (aCO2), relative expression of qPE9-1 in rice leaf was approximately tenfold higher under eCO2. Under eCO2, the growth of WT and qPE9-1-overexpressing rice was significantly higher than under aCO2. Moreover, there was no significant effect of eCO2 on the growth of qPE9-1 RNAi lines. Furthermore, WT and qPE9-1-overexpressing rice showed higher net photosynthetic rate and carbohydrate content under eCO2 than under aCO2. Moreover, the relative expression of some photosynthesis related genes in WT, but not in RNAi3 line, showed significant difference under eCO2 in RNA-seq analysis. Compared to WT and RNAi lines, the rbcL gene expression and Rubisco content of rice leaves in qPE9-1-overexpressors were higher under eCO2. Overall, these results suggest that qPE9-1 is involved in rice adaptation under elevated CO2 concentration by regulating leaf photosynthesis via moderating rice photosynthetic light reaction and Rubisco content.

Determine whether salicylic acid (SA) can alleviate the inhibitory effects of Al stress on dry matter accumulation in Panax notoginseng, and to investigate the mechanism by which the SA regulates photosynthesis and carbohydrate metabolism. Effects of SA on the biomass of P. notoginseng and the concentration of Al in leaves under Al stress were evaluated. SA and the scavenger paclobutrazol (PAC, SA synthetic inhibitor) were used to assess the effects of SA on photosynthesis and the metabolism of total nonstructural carbohydrates (TNC) in P. notoginseng. SA reduced Al by 13.23% in the leaves of P. notoginseng under Al stress. It also promoted the synthesis of carbohydrates in the leaves and their transport to the roots. Additionally, SA alleviated the Al-induced reduction of chlorophyll (Chl) by upregulating the expression of Chl synthesis genes (CHLM, CHLG, HEMB1, HEMC, and HEME) and downregulating the degradation genes (CLH2 and PPH1). Concomitantly, the rubisco activase (RCA) and rubisco enzyme activities were promoted by upregulating the expressions of the RCA, rbcL, and rbcS genes via treatment with SA, thereby restoring the synthesis and metabolism of TNC. Furthermore, SA attenuated the decrease in photosynthetic capacity and photosynthesis system II photochemistry efficiency in Al-stressed plants. Furthermore, SA significantly reduced the H2O2 concentration by 12.22% under Al stress. By regulating photosynthesis-related genes and photochemical processes, SA promoted photosynthesis and enhanced leaf carbohydrate synthesis under Al stress. Thus, SA enhanced the production of P. notoginseng biomass, ultimately reducing the inhibitory effects of Al.