Carboxylase Activity Of Rubisco Research Articles

Effect of Secondary Paper Sludge on Physiological Traits of Lactuca sativa L. under Heavy-Metal Stress.

To eliminate the negative effect of soil contamination with heavy metals on plant growth and crop yield, different methods and techniques are the subject of discussion and study. In this study, we aimed to evaluate the effect of secondary pulp and paper-mill sludge application to soil on the response of the main physiological processes such as the growth, photosynthesis, and respiration of lettuce (Lactuca sativa L.) plants to soil contamination with Pb. For the pot experiment, Pb was added to sandy loam soil at concentrations of 0, 50, and 250 mg Pb(NO3)2 per kg of the soil, and secondary sludge was added to a 0, 20, or 40% sludge solution during each plant watering. The Pb-mediated change in plant biomass allocation, decrease in the photosynthetic rate, increase in leaf respiration rate, and the degree of light inhibition of respiration were closely associated with increases in both root and shoot Pb content. For the Pb-free soil condition, secondary sludge application contributed to the allocation of plant biomass towards a greater accumulation in the shoots than in the roots. Although stomatal opening was not affected by either Pb or sludge, sludge application increased photosynthetic CO2 assimilation regardless of soil Pb content, which was associated with an increase in the electron-transport rate and carboxylase activity of Rubisco. Soil contamination with Pb significantly increased the ratio of respiration to photosynthesis, reflecting a shift in the carbon balance toward carbon losses in the leaves, but sludge application modified the coupling between the processes with a decrease in the proportion of respiratory carbon losses. The sludge-mediated recovery of the physiological processes of L. sativa reflected an increase in plant tolerance to soil contamination with heavy metals, the formation of which is associated with plant and soil adjustments initiated by secondary sludge application.

Equisetum praealtum and E. hyemale have abundant Rubisco with a high catalytic turnover rate and low CO2 affinity.

The kinetic properties of Rubisco, a key enzyme for photosynthesis, have been examined in numerous plant species. However, this information on some plant groups, such as ferns, is scarce. This study examined Rubisco carboxylase activity and leaf Rubisco levels in seven ferns, including four Equisetum plants (E. arvense, E. hyemale, E. praealtum, and E. variegatum), considered living fossils. The turnover rates of Rubisco carboxylation (kcatc) in E. praealtum and E. hyemale were comparable to those in the C4 plants maize (Zea mays) and sorghum (Sorghum bicolor), whose kcatc values are high. Rubisco CO2 affinity, estimated from the percentage of Rubisco carboxylase activity under CO2 unsaturated conditions in kcatc in these Equisetum plants, was low and also comparable to that in maize and sorghum. In contrast, kcatc and CO2 affinities of Rubisco in other ferns, including E. arvense and E. variegatum were comparable with those in C3 plants. The N allocation to Rubisco in the ferns examined was comparable to that in the C3 plants. These results indicate that E. praealtum and E. hyemale have abundant Rubisco with high kcatc and low CO2 affinity, whereas the carboxylase activity and abundance of Rubisco in other ferns were similar to those in C3 plants. Herein, the Rubisco properties of E. praealtum and E. hyemale were discussed regarding their evolution and physiological implications.

Vegetation clumping modulates global photosynthesis through adjusting canopy light environment.

The spatial dispersion of photoelements within a vegetation canopy, quantified by the clumping index (CI), directly regulates the within-canopy light environment and photosynthesis rate, but is not commonly implemented in terrestrial biosphere models to estimate the ecosystem carbon cycle. A few global CI products have been developed recently with remote sensing measurements, making it possible to examine the global impacts of CI. This study deployed CI in the radiative transfer scheme of the Community Land Model version 5 (CLM5) and used the revised CLM5 to quantitatively evaluate the extent to which CI can affect canopy absorbed radiation and gross primary production (GPP), and for the first time, considering the uncertainty and seasonal variation of CI with multiple remote sensing products. Compared to the results without considering the CI impact, the revised CLM5 estimated that sunlit canopy absorbed up to 9%-15% and 23%-34% less direct and diffuse radiation, respectively, while shaded canopy absorbed 3%-18% more diffuse radiation across different biome types. The CI impacts on canopy light conditions included changes in canopy light absorption, and sunlit-shaded leaf area fraction related to nitrogen distribution and thus the maximum rate of Rubisco carboxylase activity (Vcmax ), which together decreased photosynthesis in sunlit canopy by 5.9-7.2PgC year-1 while enhanced photosynthesis by 6.9-8.2PgC year-1 in shaded canopy. With higher light use efficiency of shaded leaves, shaded canopy increased photosynthesis compensated and exceeded the lost photosynthesis in sunlit canopy, resulting in 1.0 ± 0.12 PgC year-1 net increase in GPP. The uncertainty of GPP due to the different input CI datasets was much larger than that caused by CI seasonal variations, and was up to 50% of the magnitude of GPP interannual variations in the tropical regions. This study highlights the necessity of considering the impacts of CI and its uncertainty in terrestrial biosphere models.

Response of sink manipulation in ‘Lapins’ sweet cherry (Prunus avium L.) branches to late-deficit irrigation

Photosynthetic traits, leaf soluble sugars and fruit yield and size were evaluated in order to identify the role of early sink manipulation (girdling and fruiting spur thinning applied in winter) in modulating the effect of late-deficit irrigation (recovering 60% of crop evapotranspiration during 36 days pre-harvest) in ‘Lapins’ sweet cherry branches. Photosynthesis (PN), stomatal conductance (gs), and fruit weight were affected by both treatments, whereas intercellular CO2 concentration of leaves (Ci), mesophyll conductance (gm), Rubisco carboxylase activity (Vcmax), electron transport rate (Jmax), leaf soluble sugars and branch yield were exclusively affected by sink manipulation. The effect of sink manipulation on PN was mainly observed in the girdling treatment as it was not altered by thinning. In girdled branches, PN dropped by 34%, accompanied by a two-fold increase in leaf soluble sugars, indicating that sink feedback regulation of carbon assimilation occurred. Irrespective of the irrigation, the higher PN observed in the controls were not sufficient to achieve the fruit weight and yield of the girdled branches, indicating that fruit carbon demand in control branches was source-limited. The depressed PN by girdling was associated with significant reductions in gs, gm, Vcmax and Jmax. Since lowered PN by deficit irrigation was neither attributable to a gs-associated decrease in Ci nor to changes in any other photosynthetic variable, further research is needed to clarify this point. Results showed that irrigation deficit was sufficient to reduce PN in girdled branches, whereas it had no effect in control and thinned branches. Thus, the depressive effect of deficit irrigation on PN appeared to be exacerbated by the sink effect.

Chitosan mitigates the adverse effects and improves photosynthetic activity in rice (Oryza sativa L.) seedlings under drought condition

ABSTRACT The ability of chitosan to promote rice growth, physiological traits, and photosynthetic performance in rice seedlings under drought stress was investigated. Rice seedlings (Oryza sativa L. cv. KDML105) were treated with 100 mg l−1 low and high molecular weight (MW) chitosan via a combination of seed priming and foliar spray. The seedlings were subjected to drought stress by withholding water for 4 days, which resulted in the U-shaped (scale 5) leaf rolling. The results showed that drought significantly decreased shoot and root growth. Chitosan application, particularly with high MW chitosan, improved shoot and root growth under drought stress. Chitosan treatment also alleviated the effects of drought stress by elevating relative water content, as well as reducing electrolyte leakage and malondialdehyde content. Antioxidant enzyme activities, including guaiacol peroxidase (GPX) and ascorbate peroxidase (APX), were increased in response to chitosan. Additionally, treating the plant with chitosan improved photosynthetic efficiency as evidenced by increased CO2 response, the maximum rate of Rubisco carboxylase activity (Vcmax), and photosynthetic rate. We conclude that the exogenous application of chitosan aids the plant in coping with the severity of drought stress. While both low and high MW chitosans were effective at alleviating the effect of drought on rice seedlings, high MW chitosan might have a slight advantage with respect to increased effective duration.

A chloroplast Glycolate catabolic pathway bypassing the endogenous photorespiratory cycle enhances photosynthesis, biomass and yield in rice (Oryza sativa L.)

Photorespiration accounts for 20–50 % reduction in grain yield in C3 crops. The process is essential to remove 2-phosphoglycolate produced due to the oxygenation activity of the ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) enzyme. Attempts were made to improve photosynthesis through enriched CO2 concentration by installing numerous photorespiratory bypass modules in the chloroplast of several crops. In this study, we have introduced Escherichia coli glycolate catabolic pathway (ECGC) into rice chloroplast to bypass photorespiration partially (PB) or completely (FB). Five genes encoding glyoxylate carboligase (GCL), tartronic semialdehyde reductase (TSR), and three subunits of glycolate dehydrogenase (GDH) were introduced to get FB plants, whereas only the three subunits of GDH were introduced to get PB plants. Southern analysis confirmed stable integration of the transgenes and their expression was confirmed by RT-qPCR analysis in the T3 progenies. Both FB and PB transformed lines exhibited increased photosynthetic efficiency, biomass, and grain yield than wild type (WT) with empty vector control. The introduction of ECGC pathway favoured the carboxylase activity of RuBisCO while decreasing its oxygenase activity fostering the functioning of Calvin-Benson cycle and resulting in an increased carbon-assimilation that was manifested in their superior architecture and harvest index. These findings will support rice and related cereal crop breeding programs to increase yield under elevated temperature and arid conditions.

Carbon dots as light converter for plant photosynthesis: Augmenting light coverage and quantum yield effect

Carbon dots (CDs) with gradient-changed quantum yield (QY) were prepared by regulating the graphitic N and hydroxyl group contents. Then, the QY effect of CDs on plant photosynthesis was studied using chloroplasts and rice plants. After incubation for 2 h in the dark, CDs entered into the chloroplasts and converted ultraviolet radiation to photosynthetically active radiation. By this mechanism, CD1:0.2 (300 μg·mL−1) with a moderate QY of 46.42% significantly increased the photosynthetic activity of chloroplast (200 μg·mL−1) to reduce DCPIP and ferricyanide by 43.77% and 25.45%, respectively. After spraying on rice seedlings, CD1:0.2 (300 μg·mL−1) was evenly distributed in the leaves and resulted in maximum increases in the electron transport rate and photosynthetic efficiency of photosystem II by 29.81% and 29.88%, respectively. Furthermore, CD1:0.2 significantly increased the chlorophyll content and RuBisCO carboxylase activity of rice by 64.53% and 23.39%, respectively. Consequently, significant increases were observed in the growth of CD1:0.2-treated rice, including 18.99%, 64.31%, and 61.79% increases in shoot length, dry weights of shoot and root. These findings contribute to the exploitation of solar energy and agricultural production using CDs in the future.

Electronic structure benchmark calculations of CO2 fixing elementary chemical steps in RuBisCO using the projector-based embedding approach.

Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) is the main enzyme involved in atmospheric carbon dioxide (CO2 ) fixation in the biosphere. This enzyme catalyzes a set of five chemical steps that take place in the same active-site within magnesium (II) coordination sphere. Here, a set of electronic structure benchmark calculations have been carried out on a reaction path proposed by Gready et al. by means of the projector-based embedding approach. Activation and reaction energies for all main steps catalyzed by RuBisCO have been calculated at the MP2, SCS-MP2, CCSD, and CCSD(T)/aug-cc-pVDZ and cc-pVDZ levels of theory. The treatment of the magnesium cation with post-HF methods is explored to determine the nature of its involvement in the mechanism. With the high-level ab initio values as a reference, we tested the performance of a set of density functional theory (DFT) exchange-correlation (xc) functionals in reproducing the reaction energetics of RuBisCO carboxylase activity on a set of model fragments. Different DFT xc-functionals show large variation in activation and reaction energies. Activation and reaction energies computed at the B3LYP level are close to the reference SCS-MP2 results for carboxylation, hydration and protonation reactions. However, for the carbon-carbon bond dissociation reaction, B3LYP and other functionals give results that differ significantly from the ab initio reference values. The results show the applicability of the projector-based embedding approach to metalloenzymes. This technique removes the uncertainty associated with the selection of different DFT xc-functionals and so can overcome some of inherent limitations of DFT calculations, complementing, and potentially adding to modeling of enzyme reaction mechanisms with DFT methods.

The strategies of water–carbon regulation of plants in a subtropical primary forest on karst soils in China

Abstract. Coexisting plant species in a karst ecosystem may use diverse strategies of trade off between carbon gain and water loss to adopt to the low soil nutrient and low water availability conditions. An understanding of the impact of CO2 diffusion and maximum carboxylase activity of Rubisco (Vcmax) on the light-saturated net photosynthesis (A) and intrinsic water use efficiency (iWUE) can provide insight into physiological strategies of the water–carbon regulation of coexisting plant species used in adaptation to karst environments at the leaf scale. We selected 63 dominant species (across 6 life forms) in a subtropical karst primary forest in southwestern China, measured their CO2 response curves, and calculated the corresponding stomatal conductance to CO2 (gs), mesophyll conductance to CO2 (gm), and Vcmax. The results showed that gs and gm varied about 7.6- and 34.5-fold, respectively, and that gs was positively related to gm. The contribution of gm to the leaf CO2 gradient was similar to that of gs. gs ∕ A, gm ∕ A and gt ∕ A was negatively related to Vcmax ∕ A. The relative limitations of gs (ls), gm (lm), and Vcmax (lb) to A for the whole group (combined six life forms) were significantly different from each other (P < 0.05). lm was the largest (0.38 ± 0.12), followed by lb (0.34 ± 0.14), and ls (0.28 ± 0.07). No significant difference was found between ls, lm, and lb for trees and tree/shrubs, while lm was the largest, followed by lb and ls for shrubs, grasses, vines and ferns (P < 0.05). iWUE varied about 3-fold (from 29.52 to 88.92 µmol CO2 mol−1 H2O) across all species, and was significantly correlated with gs, Vcmax, gm ∕ gs, and Vcmax ∕ gs. These results indicated that karst plants maintained relatively high A and low iWUE through the covariation of gs, gm, and Vcmax as an adaptation to a karst environment.

Structural controls on photosynthetic capacity through juvenile‐to‐adult transition and needle ageing in Mediterranean pines

Abstract Needle photosynthetic potentials strongly vary among primary (juvenile) and secondary (adult) needles (heteroblasty) in Pinus species, but there is limited understanding of the underlying structural, diffusional and chemical controls. We studied differences in needle photosynthetic characteristics among current‐year juvenile and adult needles and among different‐aged adult needles in Mediterranean pines Pinus halepensis Mill., P. pinea L. and P. nigra J. F. Arnold subsp. salzmannii (Dunal) Franco, hypothesizing that needle anatomical modifications upon juvenile‐to‐adult transition lead to reduced photosynthetic capacity due to greater limitation of photosynthesis by mesophyll conductance and due to an increase in the share of support tissues at the expense of photosynthetic tissues. We also hypothesized that such alterations occur with needle ageing, but to a lower degree. Photosynthetic capacity per dry mass was 2.4‐ to 2.7‐fold higher in juvenile needles, and this was associated with 3.4‐ to 3.7‐fold greater mesophyll diffusion conductance, 2‐ to 2.5‐fold greater maximum carboxylase activity of Rubisco (Vcmax) and 2.2‐ to 3‐fold greater capacity for photosynthetic electron transport (Jmax). The latter differences were driven by modifications in mesophyll volume fraction and changes in the share of nitrogen between structural and photosynthetic functions. Analogous changes in photosynthetic characteristics occurred with needle ageing, but their extent was less. These results indicate that conifer foliage photosynthetic machinery undergoes a profound change from a fast return strategy in juveniles to slow return stress‐resistant strategy in adults and that this strategy shift is driven by modifications in foliage biomass investments in support and photosynthetic functions as well as by varying mesophyll diffusional controls on photosynthesis. Changes in needle morphophysiotype during tree and needle ageing need consideration in predicting changes in tree photosynthetic potentials through tree ontogeny and during and among growing seasons. A plain language summary is available for this article.

Physiological effects of short acute UVB treatments in Chenopodium quinoa Willd

Increased ultraviolet B (UVB) radiation due to global change can affect plant growth and metabolism. Here, we evaluated the capacity of quinoa to resist under short acute UVB irradiation. Quinoa was daily exposed for 30 or 60 min to 1.69 W m−2 UVB. The results showed that 30 min exposure in 9 d-course did not cause severe alterations on photosynthetic pigments and flavonoids, but a significant increase of antioxidant capacity was observed. Otherwise, 60 min UVB in 5 d-course reduced almost all these parameters except for an increase in the de-epoxidation of xanthophyll cycle pigments and led to the death of the plants. Further studies of gas exchange and fluorescence measurements showed that 30 min UVB dramatically decrease stomatal conductance, probably associated to reactive oxygen species (ROS) production. Inhibition of photosynthetic electron transport was also observed, which could be a response to reduce ROS. Otherwise, irreversible damage to the photosynthetic apparatus was found with 60 min UVB probably due to severe ROS overproduction that decompensates the redox balance inducing UVB non-specific signaling. Moreover, 60 min UVB compromised Rubisco carboxylase activity and photosynthetic electron transport. Overall, these data suggest that quinoa modulates different response mechanisms depending on the UVB irradiation dosage.

Bacterial microcompartments as metabolic modules for plant synthetic biology.

Bacterial microcompartments (BMCs) are megadalton-sized protein assemblies that enclose segments of metabolic pathways within cells. They increase the catalytic efficiency of the encapsulated enzymes while sequestering volatile or toxic intermediates from the bulk cytosol. The first BMCs discovered were the carboxysomes of cyanobacteria. Carboxysomes compartmentalize the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) with carbonic anhydrase. They enhance the carboxylase activity of RuBisCO by increasing the local concentration of CO2 in the vicinity of the enzyme's active site. As a metabolic module for carbon fixation, carboxysomes could be transferred to eukaryotic organisms (e.g. plants) to increase photosynthetic efficiency. Within the scope of synthetic biology, carboxysomes and other BMCs hold even greater potential when considered a source of building blocks for the development of nanoreactors or three-dimensional scaffolds to increase the efficiency of either native or heterologously expressed enzymes. The carboxysome serves as an ideal model system for testing approaches to engineering BMCs because their expression in cyanobacteria provides a sensitive screen for form (appearance of polyhedral bodies) and function (ability to grow on air). We recount recent progress in the re-engineering of the carboxysome shell and core to offer a conceptual framework for the development of BMC-based architectures for applications in plant synthetic biology.

Comparative modeling and molecular dynamics suggest high carboxylase activity of the Cyanobium sp. CACIAM14 RbcL protein.

Rubisco catalyzes the first step reaction in the carbon fixation pathway, bonding atmospheric CO2/O2 to ribulose 1,5-bisphosphate; it is therefore considered one of the most important enzymes in the biosphere. Genetic modifications to increase the carboxylase activity of rubisco are a subject of great interest to agronomy and biotechnology, since this could increase the productivity of biomass in plants, algae and cyanobacteria and give better yields in crops and biofuel production. Thus, the aim of this study was to characterize in silico the catalytic domain of the rubisco large subunit (rbcL gene) of Cyanobium sp. CACIAM14, and identify target sites to improve enzyme affinity for ribulose 1,5-bisphosphate. A three-dimensional model was built using MODELLER 9.14, molecular dynamics was used to generate a 100ns trajectory by AMBER12, and the binding free energy was calculated using MM-PBSA, MM-GBSA and SIE methods with alanine scanning. The model obtained showed characteristics of form-I rubisco, with 15 beta sheets and 19 alpha helices, and maintained the highly conserved catalytic site encompassing residues Lys175, Lys177, Lys201, Asp203, and Glu204. The binding free energy of the enzyme-substrate complexation of Cyanobium sp. CACIAM14 showed values around -10 kcalmol(-1) using the SIE method. The most important residues for the interaction with ribulose 1,5-bisphosphate were Arg295 followed by Lys334. The generated model was successfully validated, remaining stable during the whole simulation, and demonstrated characteristics of enzymes with high carboxylase activity. The binding analysis revealed candidates for directed mutagenesis sites to improve rubisco's affinity.

Floating and submerged leaves of Potamogeton nodosus exhibit distinct variation in the antioxidant system as an ecophysiological adaptive strategy.

During evaluations of the ecophysiological adaptations of floating and submerged leaves of Potamogeton nodosus Poir, investigations were carried to assess their antioxidant status. Floating leaves possessed a significantly higher level of C skeletons per unit of area compared with submerged leaves as they possessed greater PSI and PSII activity (hence had superior potential to harness absorbed light energy and generate assimilatory power) and carboxylase activity of Rubisco (hence superior potential to fix CO2) compared with the latter. Interestingly, submerged leaves possessed ~2 times higher H2O2 levels compared with floating leaves. In contrast, the activity of all antioxidant enzymes tested (catalase, guaiacol peroxidase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase) were significantly higher in floating leaves than in submerged leaves. Amazingly, catalase activity (a H2O2 detoxifying enzyme) was over fourfold higher in floating leaves than in submerged leaves. Among the nonenzymatic antioxidants, although levels of phenolics, ascorbate and thiols did not vary significantly between floating and submerged leaves, the level of total carotenoids was significantly higher in the former than the latter. In summary, floating leaves possess superior and efficient photosynthetic machinery for light and dark reactions, and also possess strong and superior enzymatic antioxidant machinery for scavenging reactive oxygen species and maintenance of the NAD(P)H to NAD(P)+ ratio compared with submerged leaves. Accordingly, floating leaves possessed superior potential to withstand photodamage compared with submerged leaves. We believe that excess H2O2 provides an ideal defence tool for submerged leaves to counter predators, pests and pathogens.

A reversible decrease in ribulose 1,5-bisphosphate carboxylase/oxygenase carboxylation activity caused by the aggregation of the enzyme's large subunit is triggered in response to the exposure of moderate irradiance-grown plants to low irradiance.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is highly regulated in response to fluctuations in the environment, including changes in irradiance. However, no complex data are available on Rubisco regulatory mechanisms triggered in plants which are submitted to moderate-low irradiance shift. Therefore, we investigated in a comprehensive way the changes at the level of amount of Rubisco protein, its structural organization and carboxylase activity of the holoenzyme as triggered by exposure of moderate irradiance-grown Arabidopsis thaliana plants to low irradiance conditions. An exposure of moderate irradiance-grown plants to low irradiance for a single photoperiod caused the exclusion of a certain pool of Rubisco under altered conditions owing to oxidative modifications resulting in the formation of protein aggregates involving Rubisco large subunit (LS). As a result, both initial and total Rubisco carboxylase activities were reduced, whereas Rubisco activation state remained largely unchanged. The results of the determination of reactive oxygen species indicated that a moderate/low irradiance transition had stimulated (1) O2 accumulation and we strongly suggest that Rubisco oxidative modifications leading to formation of aggregates encompassing Rubisco-LS were triggered by (1) O2 . When moderate irradiance regime was resumed, the majority of Rubisco-LS containing aggregates tended to be resolubilized, and this allowed Rubisco carboxylation activities to be largely recovered, without changes in the activation state of the enzyme. In the longer term, these results allow us to better understand a complexity of Rubisco regulatory mechanisms activated in response to abiotic stresses and during recovery from the stresses.

Assay of the Carboxylase Activity of Rubisco from Chlamydomonas reinhardtii

Assay of the Carboxylase Activity of Rubisco from Chlamydomonas reinhardtii

The photosynthetic parameters of cucumber as affected by irradiances with different red:far-red ratios

We compared photosynthetic performance between cucumber (Cucumis sativus L.) leaves acclimated to saturating irradiances with high red: far red (R:FR = 10) and normal R:FR (= 1.4) ratios. The net photosynthetic rate (PN) and stomatal conductance (gs) of the leaves acclimated to high R:FR were greater than those of the leaves acclimated to normal R:FR; the greater gs partly explains the greater PN. The greater gs of the high-R:FR-leaves probably resulted from a higher stomatal density and/or a greater size. PN of the high R:FR leaves was still greater than that of the normal R:FR leaves at the same intercellular CO2 concentration (ci). This indicates that non-stomatal factors also increased the photosynthetic capacity of the high R:FR leaves. The maximum Rubisco carboxylase activity estimated from a PN-ci curve analysis was also greater in the high R:FR leaves, however, the intrinsic water-use efficiency (WUEi = PN/gs) of the high R:FR leaves was lower than that of the normal R:FR leaves.

The Prochlorococcus carbon dioxide-concentrating mechanism: evidence of carboxysome-associated heterogeneity.

The ability of Prochlorococcus to numerically dominate open ocean regions and contribute significantly to global carbon cycles is dependent in large part on its effectiveness in transforming light energy into compounds used in cell growth, maintenance, and division. Integral to these processes is the carbon dioxide-concentrating mechanism (CCM), which enhances photosynthetic CO2 fixation. The CCM involves both active uptake systems that permit intracellular accumulation of inorganic carbon as the pool of bicarbonate and the system of HCO3 (-) conversion into CO2. The latter is located in the carboxysome, a microcompartment designed to promote the carboxylase activity of Rubisco. This study presents a comparative analysis of several facets of the Prochlorococcus CCM. Our analyses indicate that a core set of CCM components is shared, and their genomic organization is relatively well conserved. Moreover, certain elements, including carboxysome shell polypeptides CsoS1 and CsoS4A, exhibit striking conservation. Unexpectedly, our analyses reveal that the carbonic anhydrase (CsoSCA) and CsoS2 shell polypeptide have diversified within the lineage. Differences in csoSCA and csoS2 are consistent with a model of unequal rates of evolution rather than relaxed selection. The csoS2 and csoSCA genes form a cluster in Prochlorococcus genomes, and we identified two conserved motifs directly upstream of this cluster that differ from the motif in marine Synechococcus and could be involved in regulation of gene expression. Although several elements of the CCM remain well conserved in the Prochlorococcus lineage, the evolution of differences in specific carboxysome features could in part reflect optimization of carboxysome-associated processes in dissimilar cellular environments.

Pigments apparatus and anthocyanins reactions of borage to irrigation, methylalchol and titanium dioxide

This study was done to evaluate the effect of methanol and nano TiO2 foliar application on photosynthetic apparatus, anthocyanin and changes of nitrate reductase in borage (Borago officinalis L.) under deficit irrigation. Tests were done as a split factorial experiment set up as a completely randomized block design with four replications, in the year 2012, at Shahriyar City, Iran. Irrigation conditions were the factors tested in the main plots: deficit irrigation condition (irrigation every 7 days) and irrigation every 14 days. Methanol solutions 0 (control or sprayed with water), 15%, 35% and 45% (v/v) and, nanoTiO2 treatment (0 or control and nano TiO2 at concentrations of 0.01%, 0.03% and 0.05%) were tested in the sub plots. Plant characteristics under evaluation were those of; chlorophyll (Chl) a,b and total chlorophyll, Spad value, net photosynthetic rate, rubisco carboxylase activity, anthocyanin and nitrate reductase enzyme (NR). Also evaluated were the effects of interaction of deficit irrigation and methanol on all measured traits, and results determined the effect as significant with the exception of NR and interactions of deficit irrigation and nano TiO2 on all measured traits. Test results showed that maximum amount of traits at deficit irrigation was achieved by spraying with 45% v/v oncentration of methanol and nano Tio2 at the concentration of 0.05%. But the best treatments under normal irrigation were 15% v/v of methanol and 0.03% of nano Tio2. but at the methanol concentration of 45% and non-application of nano Tio2 under normal irrigation had the least effect. In summary, results of these tests determined that application of methanol and nano Tio2, can promote plant resistance to drought stress (particularly borage plants).

EFFECTS OF PHYTOHORMONES ON PROLINE CONTENT AND ANTIOXIDANT ENZYMES OF VARIOUS WHEAT CULTIVARS UNDER SALINITY STRESS

Salinity stress is one of the important agricultural problems in the world. A factorial experiment based on completely randomized design with four replications was conducted to evaluate the effects of phytohormones (gibberellic acid and abscisic acid) on the activity of antioxidant enzymes (peroxidase, superoxide dismutase and catalase), rubisco activity and content, and proline in three wheat cultivars (Gascogen, Zagros, and Kuhdasht) under control and salinity stress (3.5 and 7 dS m−1). The results showed that salinity stress (3.5 and 7 dS m−1) decreased the activity of catalase, rubisco, carboxylase, but increased peroxidase, superoxide dismutase activity and proline content. Gibberellic acid caused 58.03% increased in rubisco carboxylase activity in Zagros at 7 dS m−1 in comparison with abscisic acid under salinity stress compared with the control plants in Kuhdasht. Activity of superoxide dismutase in Kuhdasht cultivar at 7 dS m−1 salinity level showed 76.43% increased in Gascogen under salinity stress compared with the control plants with gibberellic acid application. The highest proline content as an osmolyte was found in Zagros at 7 dS m−1 salinity level with abscisic acid (194 μmol g−1 DM) application. Peroxidase activity increased 83.31% and catalase activity decreased 61.27% compared with the control plants in Zagros. Gibberellic acid application significantly prevented reduction in rubisco content under salinity stress. In conclusion, increased in peroxidase and superoxide dismutase activity and proline content decreased the adverse effects of salinity stress on studied cultivars. Also, the foliage spray of gibberellic acid enhanced and improved the growth condition. In this experiment, Zagros cultivar showed more tolerance to salinity stress than the other two cultivars.