Intracellular CO2 Research Articles

Effects of RuBisCO and CO2 concentration on cyanobacterial growth and carbon isotope fractionation.

Carbon isotope biosignatures preserved in the Precambrian geologic record are primarily interpreted to reflect ancient cyanobacterial carbon fixation catalyzed by Form I RuBisCO enzymes. The average range of isotopic biosignatures generally follows that produced by extant cyanobacteria. However, this observation is difficult to reconcile with several environmental (e.g., temperature, pH, and CO2 concentrations), molecular, and physiological factors that likely would have differed during the Precambrian and can produce fractionation variability in contemporary organisms that meets or exceeds that observed in the geologic record. To test a specific range of genetic and environmental factors that may impact ancient carbon isotope biosignatures, we engineered a mutant strain of the model cyanobacterium Synechococcus elongatus PCC 7942 that overexpresses RuBisCO across varying atmospheric CO2 concentrations. We hypothesized that changes in RuBisCO expression would impact the net rates of intracellular CO2 fixation versus CO2 supply, and thus whole-cell carbon isotope discrimination. In particular, we investigated the impacts of RuBisCO overexpression under changing CO2 concentrations on both carbon isotope biosignatures and cyanobacterial physiology, including cell growth and oxygen evolution rates. We found that an increased pool of active RuBisCO does not significantly affect the 13 C/12 C isotopic discrimination (εp ) at all tested CO2 concentrations, yielding εp of ≈ 23‰ for both wild-type and mutant strains at elevated CO2 . We therefore suggest that expected variation in cyanobacterial RuBisCO expression patterns should not confound carbon isotope biosignature interpretation. A deeper understanding of environmental, evolutionary, and intracellular factors that impact cyanobacterial physiology and isotope discrimination is crucial for reconciling microbially driven carbon biosignatures with those preserved in the geologic record.

The emergence and advancement of Tsuji-Trost reaction triggered carbon monoxide recognition and bioimaging.

Considering that carbon monoxide is both a vital gasotransmitter and an obnoxious gas, tremendous efforts have been dedicated toward its recognition through various methods. However, the fluorescent light-up approach through the exploration of optical markers remains one of the most convenient methods owing to its several advantages. Amongst the different approaches towards the development of CO responsive optically active molecular markers, the Tsuji-Trost reaction-based CO recognition strategy has remained one of the most significant areas of interest across researchers working in this field. However, there have been no attempts to exclusively summarize the commendable work done in this area yet. The current review, therefore, attempts to summarize the developments of various optical probes following this reaction strategy until the year 2022. This review provides detailed mechanistic insights into the Tsuji-Trost mediated CO detection strategy. Besides, discussions on the strategic development and employment of probes based on various allyl derivatives - allyl carbamate/carbonate/ethers - will provide a thorough understanding of the detection method. The significant advancements of the Tsuji-Trost reaction as an interesting strategy that is accepted and extensively explored for monitoring CO in various media including air, aqueous solutions and living systems have been elaborately discussed. Various potential applications and utilization of these developed fluorogenic probes for tracing CO in different living systems have been examined systematically. Moreover, monitoring of exogenous/endogenous CO levels, modulation of intracellular CO concentration under various induced conditions and bioimaging of CO in in vivo models have also been detailed here. Briefly, this review summarizes the current prospects of this detection method and the future directions in related fields.

Physiological and Yield Performance Is Partially Linked to Water Use Efficiency of Eggplant Genotypes in a High-Tech Glasshouse

Eggplant (Solanum melongena L.) has become an increasingly common vegetable grown in glasshouses. This study emphasized on the physiological traits and productivity of three eggplant cultivars (Longa, Lydia, and Tracey) in a high-tech glasshouse to determine the genotypic differences of agronomical, morphological, and physiological responses. The physiological parameters as well as the productivity of these eggplant cultivars were evaluated. The results showed that Tracey had significantly higher leaf growth than Longa and Lydia. Longa exhibited significantly higher values of net CO2 assimilation (A), stomatal conductance (gs), and transpiration rate (Tr) than Tracey, whereas Tracey showed significantly larger gs, Tr, and intracellular CO2 concentration (Ci) than Lydia. Tracey showed a significantly higher number of flowers per node compared to the two other varieties, but the number of fruits did not statistically differ among cultivars. Tracy produced the highest yield (fruit weight and fruit yield per m2) due to the significantly higher leaf length and leaf expansion rate despite the lowest level of A among the three cultivars. Interestingly, the higher yield of Tracey translated into better water use efficiency (WUE) in the agronomic term, but its intrinsic WUE (A/gs) was the lowest among the three cultivars. However, significant correlations between photosynthetic parameters and WUE were only found in certain stages of eggplant growth. Therefore, further research work with an emphasis on the source and sink partitioning of a large number of eggplant genotypes is required to investigate the varietal performance of greenhouse eggplants. Then, the information can be translated into protected cropping to set up the growth benchmark for large-scale sustainable production of eggplants with better yield and less water consumption for the horticultural industry.

The effect of CO2 concentration on carbon isotope discrimination during photosynthesis in Ginkgo biloba: implications for reconstructing atmospheric CO2 levels in the geologic past

Some experiments and observations of free-living plants have found that increasing atmospheric concentration of CO2 (pCO2) is directly correlated with increasing discrimination against 13C during photosynthesis (Δ13C) in C3 plants. The inverted form of this correlation has been used to estimate pCO2 in the geological past (i.e. the C3 plant proxy), but there has been little experimental work to establish the relative importance of pCO2 as a driver of discrimination in more natural settings and over a range of pCO2 relevant to the deep-time geologic record. Here we report on an experiment exploring the relationship between pCO2 and Δ13C in Ginkgo biloba, a plant long used to infer past CO2 levels because of the strong similarity of extant to fossil Ginkgo and the abundance of Ginkgo fossils with preserved cuticle from late Mesozoic and Cenozoic periods of warm global climate.We grew Ginkgo biloba plants for three years under ambient pCO2 (∼425 ppm) and elevated levels (∼600, ∼800, and ∼ 1000 ppm) while measuring the carbon isotope composition of air (δ13Cair) and leaves (δ13Cleaf) as well as the ratio of internal to external CO2 concentration (ci/ca), maximum photosynthetic assimilation rate (Amax), C:N ratio, and leaf mass per area (LMA). We found no significant relationship between pCO2 and Δ13Cleaf or ci/ca. We did find a direct correlation of pCO2 with Amax, LMA, and C:N ratio. The lack of increase in Δ13Cleaf with rising pCO2 may result from the lack of change in ci/ca, thicker leaves that slow the rate of diffusion of CO2 through the leaf to mesophyll cells, higher Amax that drives more rapid consumption of intracellular CO2 and/or changes in the relative proportions of starches, lipids or other compounds that have distinct isotopic compositions.Our results, along with a compilation of data from the literature on Δ13Cleaf in many different types of C3 plants, suggest that Δ13Cleaf does not consistently increase with increasing pCO2. Rather, there is a diversity of responses, both positive and negative, that are not clearly related to taxonomic group or growth form but may reflect changes in leaf structure, stomatal response and Amax under higher pCO2. Given the complex relationship between Δ13Cleaf and pCO2 in living plants we consider Δ13Cleaf of fossil plants to be an unreliable proxy for paleo-atmospheric pCO2.

The Spectral Compositions of Light Changes Physiological Response of Chinese Cabbage to Elevated Ozone Concentration.

The effects of ozone combined with other environmental factors remain an important topic of the research, both in connection with climate change and the possibility of using modern solutions in horticulture. In our experiment, we compared the influence of ozone (100 ppb) on photosynthesis and changes in the pigment composition of Chinese cabbage (Brassica rapa subsp. pekinensis) leaves depending on the spectral composition of light. We used white LED light (WL), a combination of red + green + blue (RGBL) with a dominant red component and white +blue (WBL) with a dominant blue component in comparison with the classic sodium lamp lighting (yellow light—YL). The values of the parameters describing the light-dependent phase of photosynthesis and the parameters of the gas exchange, as well as non-photosynthesis pigment contents, show that the spectral composition strongly differentiates the response of Chinese cabbage leaves to ozone. In general, the efficiency of photochemical reactions was the highest in YL, but after O3 fumigation, it decreased. In plants growing in WL and WBL, the increase of O3 concentration stimulated light photosynthesis reactions and led to the enhancement of transpiration, stomatal conductance and intracellular CO2 concentration. Changes in photosynthetic activity were accompanied by an increase in the content of anthocyanins and flavonols.

Spermine-mediated polyamine metabolism enhances arsenic-stress tolerance in Phaseolus vulgaris by expression of zinc-finger proteins related genes and modulation of mineral nutrient homeostasis and antioxidative system

The contamination of groundwater and agricultural land by metalloids especially arsenic (As) is one of the most serious threats to people and plants worldwide. Therefore, the present study was design to explore the role of spermine (Spm)- mediated polyamine metabolism in the alleviation of arsenic (As) toxicity in common bean (Phaseolus vulgaris L.). It was noted that As stress caused reduction in the intracellular CO2 concentration, stomatal conductivity and transpiration rate as compared to the control treatment and also impairedplant growth attributes and mineral nutrient homeostasis (sulfur, phosphorus, potassium and calcium). However, the exogenous application of Spm resulted in a considerable enhance in the content of glutathione and nitric oxide, and the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione-reductase (GR), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR) in P. vulgaris seedlings grown As-contaminated soil. In addition, Spm application significantly improved the endogenous production of putrescine and spermidine accompanied along with reduction in malondialdehyde, electrolyte leakage, hydrogen peroxide, superoxide level besides enhanced methylglyoxal (MG) detoxification. Moreover, Spm treatment elevated the expression level of zinc-finger proteins related genes (PvC3H24, PvC3H25, PvC3H26 and PvC3H27) involved in abiotic stress response. The study concluded that Spm acted as an enhancing agent and improved tolerance to As-toxicity by upregulating the expression of zinc-finger proteins related genes, polyamine metabolism, Mg detoxification and antioxidant system in P. vulgaris.

Solid-phase synthesis of peptides with azopyridine side-chains for Mn(i)–CO binding and red-light responsive CO release

A highly efficient one-pot solid-phase synthesis of peptides with azopyridine is reported. When conjugated with the Mn–CO moiety, the resulting peptide- photoCORMs were able to achieve targeted intracellular CO release upon red light illumination.

Archaeal tetraether lipids and their biphytane carbon isotope composition in sediments along an estuarine biogeochemical gradient

The stable carbon isotopic composition of Thaumarchaeota-produced crenarchaeol (δ13Ccren) is thought to reflect the δ13C of dissolved inorganic carbon (DIC) and is valuable in carbon cycle research. Recently, an isotope flux-balance model was proposed that δ13Ccren is dependent on passive CO2 uptake and a slow rate of intracellular conversion to HCO3−, which has been validated in open ocean environments. However, further studies are required in environments with larger ranges of aqueous CO2 and diverse archaeal communities to examine whether the δ13Ccren value could still be predicted by the model. Here, we report δ13C values of biphytanes chemically released from the archaeal tetraether lipids (i.e., GDGTs) in sediments along a transect exhibiting shifts in the archaeal community and showing gradients of salinity, pH, and CO2 in the Pearl River Estuary, South China. Methanogenic and methanotrophic Euryarchaeota are present in the upper estuary, although not significant, as revealed by the elevated relative abundances of GDGT-0 and higher values of methane index in suspended particulate matter (SPM) and surface sediments, as well as the more 13C-depleted C40:0, C40:1, and C40:2 biphytanes than the C40:3 biphytane released from sedimentary GDGTs. Toward the lower estuary and coastal sea, GDGT distributions in SPM and sediments tend to indicate archaeal communities under normal marine conditions. However, there are still differences in δ13C values between C40:0 and C40:3 biphytanes by up to 2.4‰ in sediments, although C40:1, C40:2, and C40:3 were similar in δ13C, likely due to the existence of marine group II Euryarchaeota. Along such a physicochemical and biogeochemical gradient, the values of sedimentary δ13C40:3 increase monotonically with the increase of mean annual pH and the decrease of mean annual CO2. This phenomenon resembles the reported δ13CGDGT profiles, along with the variations in pH and CO2, in water column in the open ocean, and hence consistent in direction with the isotope flux-balance model for Thaumarchaeota lipids. However, our estimated apparent biosynthetic isotope effect (εAr) of crenarchaeol, ranging from 15.2‰ to 19.7‰, is mostly lower than those estimated in the open ocean. With the constraints of thaumarchaeal growth rates in such a dynamic estuarine environment as well as those in the open ocean, we suggest slight reductions in catalytic efficiency and intracellular kinetic isotope effect of intracellular CO2 hydration relative to previously employed values. Such modifications would slightly change the sensitivities of εAr to archaeal growth rate and ambient CO2 concentration but might be more suitable for variable hydrology and community environments.

Acetate-assisted carbon monoxide fermentation of Clostridium sp. AWRP

Acetogens are of great interest on conversion of synthesis gas in that they can efficiently utilize CO-containing gases to produce C2 and higher metabolic products. However, high concentration of CO is known to inhibit the reduction of CO2 into formate, thereby diminishing an overall carbon fixation rate. We report that acetate supplementation can be a simple, effective approach to mitigating CO inhibition in Clostridium sp. AWRP (hereinafter called AWRP). The added acetate rapidly reduced into ethanol by the AWRP cells, which coincided with CO oxidation. From stoichiometric calculations, the acetate reduction was observed to allow carbon fixation, indicating that the CO oxidation might reduce the intracellular CO levels below inhibitory levels. Furthermore, AWRP exhibited an 83 % higher maximum specific growth rate (μmax) in the acetate-supplemented bottle cultures than in the control. In the bioreactor experiments, the AWRP culture with exogenous acetate displayed 2.9- and 2.3-fold higher titers of ethanol (232 mM) and 2,3-butanediol (23 mM), respectively, as well as μmax (2.6-fold) and maximum cell density (1.9-fold), than without acetate supplementation. These results indicate that this approach can be applied to various fermentative experiments using CO-containing gases to shorten the overall cultivation time.

Exogenous nitric oxide alleviates manganese toxicity in bean plants by modulating photosynthesis in relation to leaf lipid composition.

Nitric oxide (NO) is a signaling molecule controlling several steps of plant development and defense process under stress conditions. NO-induced alleviation of manganese (Mn) toxicity was investigated on bean plants submitted for 28days to 500µM MnCl2. Manganese excess decreased plant dry weight and elongation and increased levels of reactive oxygen species and lipid peroxidation leading to up-regulation of superoxide dismutase, catalase, and ascorbate peroxidase activities. The inhibitory effects of Mn on plant growth were associated to reduction of light-saturated carbon assimilation (Amax), stomatal conductance (gs), and transpiration (E). By contrast, Mn induced significant increase in the apparent quantum yield (ɸ) and light compensation point (LCP). Interestingly, intracellular CO2 (Ci) remains stable under Mn stress. Concomitantly, leaf membrane lipids have drastically reduced under high Mn concentration. After Mn exposition, leaf fatty acids exhibited a significant loss of linolenic acid, accompanied by an accumulation of palmitoleic, stearic, and linoleic acids leading to alteration of lipid desaturation. NO supply reversed Mn toxicity as evidenced by enhancement of growth biomass and recovery of Amax, E, ɸ, and LCP. Similarly, NO addition has positive effects on leaf lipid content and composition leading to restoration of lipid unsaturation. The modulation of fatty acid composition can be a way to reduce leaf membrane damages and maintain optimal photosynthesis and plant growth. Despite the absence of enough evidences in how NO is involved in lipid and photosynthesis recovery under Mn stress conditions, it is assumed that NO beneficial effects are attributable to NO/Mn cross-talk.

Cacao (Theobroma cacao L.) Response to Water Stress: Physiological Characterization and Antioxidant Gene Expression Profiling in Commercial Clones.

The increase in events associated with drought constraints plant growth and crop performance. Cacao (Theobroma cacao L.) is sensitive to water deficit stress (DS), which limits productivity. The aim of this research was to characterise the response of seven (CCN51, FEAR5, ICS1, ICS60, ICS95, EET8, and TSH565) commercially important cacao clones to severe and temporal water deficit stress. Ten-month-old cacao trees were submitted to two treatments: well-watered and water-stressed until the leaf water potential (Ψleaf) reached values between −3.0 and −3.5 MPa. The effects of hydric stress on water relations, gas exchange, photochemical activity, membrane integrity and oxidative stress-related gene expression were evaluated. All clones showed decreases in Ψleaf, but TSH565 had a higher capacity to maintain water homeostasis in leaves. An initial response phase consisted of stomatal closure, a general mechanism to limit water loss: as a consequence, the photosynthetic rate dropped by approximately 98% on average. In some clones, the photosynthetic rate reached negative values at the maximum stress level, evidencing photorespiration and was confirmed by increased intracellular CO2. A second and photosynthetically limited phase was characterized by a drop in PSII quantum efficiency, which affected all clones. On average, all clones were able to recover after 4 days of rewatering. Water deficit triggered oxidative stress at the early phase, as evidenced by the upregulation of oxidative stress markers and genes encoding ROS scavenging enzymes. The effects of water deficit stress on energy metabolism were deduced given the upregulation of fermentative enzyme-coding genes. Altogether, our results suggest that the EET8 clone was the highest performing under water deficit while the ICS-60 clone was more susceptible to water stress. Importantly, the activation of the antioxidant system and PSII repair mechanism seem to play key roles in the observed differences in tolerance to water deficit stress among clones.

Ectomycorrhizal Inoculation Enhances the Salt Tolerance of Quercus mongolica Seedlings.

Salt stress harms the growth and development of plants, and the degree of soil salinization in North China is becoming increasingly severe. Ectomycorrhiza (ECM) is a symbiotic system formed by fungi and plants that can improve the growth and salt tolerance of plants. No studies to date have examined the salt tolerance of Quercus mongolica, a typical ectomycorrhizal tree species of temperate forests in the northern hemisphere. Here, we inoculated Q. mongolica with two ectomycorrhizal fungi (Gomphidius viscidus; Suillus luteus) under NaCl stress to characterize the effects of ECM. The results showed that the symbiotic relationship of Q. mongolica with G. viscidus was more stable than that with S. luteus. The cross-sectional area of roots increased after inoculation with the two types of ectomycorrhizal fungi. Compared with the control group, plant height, soluble sugar content, and soluble protein content of leaves were 1.62, 2.41, and 2.04 times higher in the G. viscidus group, respectively. Chlorophyll (Chl) content, stomatal conductance (Gs), and intracellular CO2 concentration (Ci) were significantly higher in Q. mongolica inoculated with ectomycorrhizal fungi than in the control, but differences in the net photosynthetic rate (Pn), transpiration rate (Tr), and photosystem II maximum photochemical efficiency (Fv/Fm) were lower. The relative conductivity of Q. mongolica inoculated with the two ectomycorrhizal fungi was consistently lower than that of non-mycorrhizal seedlings, with the effect of G. viscidus more pronounced than that of S. luteus. The malondialdehyde (MDA) content showed a similar pattern. Peroxidase (POD) and catylase (CAT) levels in mycorrhizal seedlings were generally higher than those of non-mycorrhizal seedlings under normal conditions, and were significantly higher than those of non-mycorrhizal seedlings on the 36th and 48th day after salt treatment, respectively. Overall, the results indicated that the salt tolerance of Q. mongolica seedlings was improved by ectomycorrhizal inoculation.

Physiological and metabolic changes in two Himalayan medicinal herbs under drought, heat and combined stresses.

The online version contains supplementary material available at 10.1007/s12298-021-01027-w.

The Effect of the Foliar Application of Biostimulants and Fertilisers on the Growth and Physiological Parameters of Maiden Apple Trees Cultivated with Limited Mineral Fertilisation

The article describes an experiment conducted on maiden apple trees of selected cultivars growing in a nursery. The aim of the study was to investigate how the foliar application of four biostimulants (Aminoplant 0.4%, Biamino Plant 0.2%, Bispeed 0.2% and Fylloton 0.4%) and two fertilisers (Basfoliar 6-12-6 and Basfoliar 12-4-6+S both at a concentration of 0.5%) affected the growth of the trees cultivated with the mineral fertilisation reduced by half. The plants were sprayed with the preparations and fertilisers four times at three-week intervals, between late May and late July. Selected parameters of the plants’ physiological processes were also assessed: net photosynthetic rate (Pn), transpiration rate (E), stomatal conductance (C) and intracellular CO2 (I). The foliar application of all the biostimulants and fertilisers significantly improved the growth of the maiden apple trees. The lowest values of the plant growth parameters were noted in the control combination, which was treated with a full dose of mineral fertiliser. The foliar spraying of the apple trees particularly improved the total length and number of side shoots and the fresh weight of maiden apple trees. The apple tree cultivars differed in their growth parameters, and the influence of individual foliar treatments was not conclusive. The foliar application of selected preparations intensified the leaf transpiration coefficient and the internal concentration of carbon dioxide, but it did not increase the net photosynthesis intensity or stomatal conductance.

Easily Available, Amphiphilic Diiron Cyclopentadienyl Complexes Exhibit in Vitro Anticancer Activity in 2D and 3D Human Cancer Cells through Redox Modulation Triggered by CO Release.

A straightforward two‐step procedure via single CO removal allows the conversion of commercial [Fe2Cp2(CO)4] into a range of amphiphilic and robust ionic complexes based on a hybrid aminocarbyne/iminium ligand, [Fe2Cp2(CO)3{CN(R)(R’)}]X (R, R’=alkyl or aryl; X=CF3SO3 or BF4), on up to multigram scales. Their physicochemical properties can be modulated by an appropriate choice of N‐substituents and counteranion. Tested against a panel of human cancer cell lines, the complexes were shown to possess promising antiproliferative activity and to circumvent multidrug resistance. Interestingly, most derivatives also retained a significant cytotoxic activity against human cancer 3D cell cultures. Among them, the complex with R=4‐C6H4OMe and R’=Me emerged as the best performer of the series, being on average about six times more active against cancer cells than a noncancerous cell line, and displayed IC50 values comparable to those of cisplatin in 3D cell cultures. Mechanistic studies revealed the ability of the complexes to release carbon monoxide and to act as oxidative stress inducers in cancer cells.

Alleviation of Salt-Induced Adverse Effects on Gas Exchange, Photosynthetic Pigments Content and Chloroplast Ultrastructure in Gerbera Jamesonii L. by Exogenous Salicylic Acid Application

Aims: The effects of exogenously applied salicylic acid (SA) on gas exchange characteristics, photosynthetic pigments and chloroplast ultrastructure were investigated in gerbera at their reproductive stage under salt-stressed conditions.
 Methodology: A pot experiment was conducted under glasshouse conditions at the Zhejiang University, Hangzhou, China, (30° N/120° E) between February 2008 and March 2009.Plants, pretreated with foliar applications of 0, 0.5, and 1.0 mmoldm-3 SA at the onset of flower initiation were irrigated with 100 mmoldm-3NaCl(aq) for two weeks, starting after three days from the SA pretreatment. Control did not receive either NaCl or SA.Photosynthetic rate, gas exchange, photosynthetic pigments content and chloroplast ultrastructure were investigated against treatments. All data were subjected to analysis of variance (ANOVA) and Generalized Linear Model (GLM) using SAS statistical software. Pearson’s correlation test was carried out to study the relationships among the parameters. The means were compared using Duncan’s multiple range test (DMRT). For all the tests, P< .05 was considered statistically significant.
 Results: Salt stress adversely affected the gas exchange characteristics, photosynthetic pigment contents and chloroplast ultrastructure. SA application significantly increased the net photosynthesis, stomatal conductivity, intra-cellular CO2 content and transpiration rate but decreased the stomatal limitation, compared to those of untreated salt-stressed plants. Further, the enhanced photosynthetic pigment contents and notably undamaged chloroplast ultrastructure were evident of the ameliorative effects of SA on photosynthetic system under salt stress. Of the two concentrations tested, 0.5 mmoldm-3 SA concentration seemed to have greater effect throughout the experiment showing no significant variation from control in some attributes (chlorophyll contents and chloroplast ultrastructure).
 Conclusion: Responses of plants pretreated with SA spraying and significant correlation among them plausibly suggest SA-induced enhancement of photosynthetic system as another target for conferring salt tolerance in crop plants.

Mixotrophic growth of the extremophile Galdieria sulphuraria reveals the flexibility of its carbon assimilation metabolism.

Summary Galdieria sulphuraria is a cosmopolitan microalga found in volcanic hot springs and calderas. It grows at low pH in photoautotrophic (use of light as a source of energy) or heterotrophic (respiration as a source of energy) conditions, using an unusually broad range of organic carbon sources. Previous data suggested that G. sulphuraria cannot grow mixotrophically (simultaneously exploiting light and organic carbon as energy sources), its photosynthetic machinery being repressed by organic carbon.Here, we show that G. sulphuraria SAG21.92 thrives in photoautotrophy, heterotrophy and mixotrophy. By comparing growth, biomass production, photosynthetic and respiratory performances in these three trophic modes, we show that addition of organic carbon to cultures (mixotrophy) relieves inorganic carbon limitation of photosynthesis thanks to increased CO2 supply through respiration. This synergistic effect is lost when inorganic carbon limitation is artificially overcome by saturating photosynthesis with added external CO2.Proteomic and metabolic profiling corroborates this conclusion suggesting that mixotrophy is an opportunistic mechanism to increase intracellular CO2 concentration under physiological conditions, boosting photosynthesis by enhancing the carboxylation activity of Ribulose‐1,5‐bisphosphate carboxylase‐oxygenase (Rubisco) and decreasing photorespiration.We discuss possible implications of these findings for the ecological success of Galdieria in extreme environments and for biotechnological applications.

Linking exogenous foliar application of glycine betaine and stomatal characteristics with salinity stress tolerance in cotton (Gossypium hirsutum L.) seedlings

BackgroundGlycine betaine (GB) plays a crucial role in plants responding to abiotic stresses. Studying the physiological response of cotton seedlings to exogenous GB under salt stress provides a reference for the application of GB to improve the resistance of cotton seedlings under salt stress. The purpose of this research is to examine the impacts of foliar-applied GB on leaf stomatal structure and characteristics, gas exchange and chlorophyll fluorescence characteristics and plant growth indicators of Gossypium hirsutum L. under NaCl stress conditions.ResultsUnder the salinity of 150 mM, the four concentrations of GB are 0, 2.5, 5, and 7.5 mM, and the control (CK) was GB-untreated non-saline. Salt stress negatively affected leaf stomata as well as gas exchange and chlorophyll fluorescence and decreased plant growth parameters of cotton seedlings. The treatment with 5 mM GB significantly increased the evolution of photosynthetic rate (Pn), transpiration rate (Tr), intracellular CO2 concentration (Ci) and stomatal conductance (gs) compared to the GB-untreated saline treatment. The Exogenous foliar-applied GB has sustainably decreased the carboxylation efficiency (Pn/Ci) and water use efficiency (WUE). The concentration of 5 mM GB leads to a significant improvement of leaf stomatal characteristics. The leaf gas exchange attributes correlated positively with stomatal density (SD), stomatal length (SL) and stomatal with (SW).ConclusionThe overall results suggested that exogenous foliar supplementation with GB can effectively alleviate the damage of salt stress to cotton seedlings. The effect of applying 5 mM GB could be an optional choice for protecting cotton seedlings from NaCl stress through promoting the stomatal functions, photosynthetic activities and growth characteristics.

In vitro acclimatization of Curcuma longa under controlled iso-osmotic conditions.

In vitro acclimatization has been validated as the successful key to harden the plantlets before transplanting to ex vitro conditions. In the present study, we investigated the potential of different sugar types (glucose, fructose, galactose, sucrose) in regulating morphological, physiological and biochemical strategies, survival percentage and growth performance, and rhizome traits of turmeric under iso-osmotic potential. Leaf greenness (SPAD value) in acclimatized plantlets (4% glucose; -1.355 MPa osmotic potential) of 'ST018' was retained and greater than in 'PB009' by 1.69-fold, leading to maintain high Fv/Fm (maximum quantum yield of PSII), ΦPSII (photon yield of PSII) and Pn (net photosynthetic rate) levels, and retained shoot height, leaf length, leaf width, shoot fresh weight and shoot dry weight after one month upon transplanting to ex vitro conditions. In addition, Pn, Ci (intracellular CO2), gs (stomatal conductance) and E (transpiration rate) in acclimatized plantlets (6% sucrose; -1.355 MPa osmotic potential) of 'PB009' were stabilized as physiological adapted strategies, regulating the shoot and root growth and fresh and dry weights of mini-rhizome. Interestingly, the accumulation of total curcuminoids in mini-rhizome derived from 6% sucrose acclimatized plantlets of 'ST018' was greater than in 'PB009' by 3.76-fold. The study concludes that in vitro acclimation of turmeric 'PB009' and 'ST018' using 6% sucrose and 4% glucose, respectively, promoted percent survival, physiological adaptations, and overall growth performances under greenhouse conditions.

Alleviating Cr(VI) stress in horse gram (Macrotyloma uniflorum Var. Madhu) by native Cr-tolerant nodule endophytes isolated from contaminated site of Sukinda.

Sukinda chromite mine of Odisha is a heavily polluted site, generating huge overburden dumps. The present experiment was designed to evaluate the potential of two native nodule endophytic bacterial strains, viz. Bacillus aryabhattai AS03 (MT645244) and Rhizobium pusense AS05 (MT645243), isolated from contaminated sites to be considered remediation tool to minimize the effect of Cr toxicity on Macrotyloma uniflorum var. Madhu. The two nodule endophytic bacterial strains AS03 and AS05 exhibited tolerance to 1800 and 3000 ppm of Cr(VI) respectively in vitro when cultured alone. AAS analysis confirmed higher accumulation of Cr(VI) in roots and less accumulation in shoots which is dose-specific (bio-inoculant) either treated alone or combined. Complete absence of Cr accumulation approximately 99% in shoots of Macrotyloma was observed owing to synergistic effect of both the strains (biochar-based formulation). This study also suggests increased shoot and root length, nodule nos., and leghemoglobin content of the plant at 60 days indicating the plant growth-promoting effects of both the strains. ROS and antioxidant enzymes of the plant recorded decreasing trend in inoculated plants. However, a significant increment in transpiration rate, total photosynthetic rate, intracellular CO2 conc., and stomatal conductance in leaves was observed owing to dual inoculation. Our findings corroborate the supremacy of synergistic effect of both the strains applied in the form of biochar-based biofertilizer in enhancing growth and tolerance index of M. uniflorum cultivated in Cr(VI)-stressed soil. This investigation depicts the efficiency of the two nodule bacteria as a mixed inoculant to alleviate Cr toxicity and making the seeds safe for consumption.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-021-13009-2.