Co-function of C3-and C4-photosynthetic pathways in C3, C4 and C3-C4 intermediate Flaveria species

The potential for C₄ photosynthesis was investigated in five C₃-C₄ intermediate species, one C₃ species, and one C₄ species in the genus Flaveria, using ¹⁴CO₂ pulse-¹²CO₂ chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating ¹⁴CO₂ into the C₄ acids malate and aspartate, following an 8-s pulse. The proportion of ¹⁴C label in these C₄ products ranged from 50–55% to 20–26% in the C₃-C₄ intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, ¹⁴CO₂ into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C₄ photosynthesis among the intermediate species based on the apparent rate of conversion of ¹⁴C label from the C₄ cycle to the C₃ cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C₄-cycle products and an increase in percentage label in C₃-cycle products during chase periods with ¹²CO₂, although the rate of change was slower than in the C₄ species, F. palmeri. In these C₃-C₄ intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C₃-C₄ intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C₄-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C₄ and C₃ cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C₃ species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C₄-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O₂, the absorbed quantum yields for CO₂ uptake (in mol CO₂·[mol quanta]^-1) averaged 0.053 in F. cronquistii (C₃), 0.051 in F. trinervia (Spreng.) Mohr (C₄), 0.052 in F. ramosissima (C₃-C₄), 0.051 in F. anomala (C₃-C₄), 0.050 in F. linearis (C₃-C₄), 0.046 in F. floridana (C₃-C₄), and 0.044 in F. pubescens (C₃-C₄). In 2% O₂ an enhancement of the quantum yield was observed in all of the C₃-C₄ intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O₂ were intermediate in value to the C₃ and C₄ species, indicating a co-function of the C₃ and C₄ cycles in CO₂ assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O₂ presumably reflect an ineffcient transfer of carbon from the C₄ to the C₃ cycle. The response of the quantum yield to four increasing O₂ concentrations (2–35%) showed lower levels of O₂ inhibition in the C₃-C₄ intermediate F. ramosissima, relative to the C₃ species. This indicates that the co-function of the C₃ and C₄ cycles in this intermediate species leads to an increased CO₂ concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O₂.Abbreviations PEP phosphoenolpyruvate - PGA 3-phosphoglycerate - RuBP ribulose-1,5-bisphosphate     

Demonstration in human plasma of a form of C3 that has the conformation of "C3b-like C3".

Disruption of the thioester in native C3 yields a C3 molecule that functionally resembles C3b. It has been proposed that this C3 molecule (iC3) plays a key role in initiation of the alternative pathway of the C system. However, its presence in plasma has never been demonstrated. We investigated the presence of iC3 in plasma, using mAb that recognize iC3 as well as C3 activation products but not native C3. One of these mAb, anti-C3-5, which binds iC3 via its C3a moiety, was used together with polyclonal 125I-anti-C3c to develop a RIA for iC3. Plasma incubated with methylamine yielded a strong response in this RIA, whereas neither fresh plasma nor serum in which the C system had been activated by incubation with aggregated IgG, did show this strong response. The specificity of this RIA was further demonstrated by additional experiments including experiments with purified preparations of the various forms of C3. Mean level of iC3 in freshly obtained plasma samples from 10 normal donors was 27 nmol/liter, which is 0.49% of total C3. Analysis by SDS-PAGE of C3 species that had been immunoprecipitated by mAb antiC3-5, revealed that some iC3 consisted of C3 molecules with an intact alpha-chain whereas another part consisted of iC3 molecules with an alpha-chain that had been cleaved by factor I. Thus, this study shows that fresh human plasma contains a C3 species with the conformation of "C3b-like C3" (iC3).     

Effects of irradiance and temperature on photosynthesis in C3, C4 and C3/C4 Panicum species

Species in the Laxa and Grandia groups of the genus Panicum are adapted to low, wet areas of tropical and subtropical America. Panicum milioides is a species with C₃ photosynthesis and low apparent photorespiration and has been classified as a C₃/C₄ intermediate. Other species in the Laxa group are C₃ with normal photorespiration. Panicum prionitis is a C₄ species in the Grandia group. Since P. milioides has some leaf characteristics intermediate to C₃ and C₄ species, its photosynthetic response to irradiance and temperature was compared to the closely related C₃ species, P. laxum and P. boliviense and to P. prionitis. The response of apparent photosynthesis to irradiance and temperature was similar to that of P. laxum and P. boliviense, with saturation at a photosynthetic photo flux density of about 1 mmol m^-2 s^-1 at 30°C and temperature optimum near 30°C. In contrast, P. prionitis showed no light saturation up to 2 mmol m^-2 s^-1 and an optimum temperature near 40°C. P. milioides exhibited low CO₂ loss into CO₂-free air in the light and this loss was nearly insensitive to temperature. Loss of CO₂ in the light in the C₃ species, P. laxum and P. boliviense, was several-fold higher than in P. milioides and increased 2- to 5-fold with increases in temperature from 10 to 40°C. The level of dark respiration and its response to temperature were similar in all four Panicum species examined. It is concluded that the low apparent photorespiration in P. milioides does not influence its response of apparent photosynthesis to irradiance and temperature in comparison to closely related C₃ Panicum species.Abbreviations AP apparent photosynthesis - I CO₂ compensation point - gl leaf conductance; gm, mesophyll conductance - PPFD photosynthetic photon flux density - PR apparent photorespiration rate - RuBPC sibulose bisphosphate carboxylase     

C3 polymorphism in Greece

The polymorphism of the third component of the human complement (C3) was investigated in a sample of 1,055 unrelated healthy individuals from nine different areas of Greece. The estimated gene frequencies were: C3S = 0.786 and C3F = 0.211. Three individuals were found to have rare variant C3 types. The allele frequencies resemble those reported for other Caucasian populations.     

C3 photosynthesis in silico

A computer model comprising light reactions, electron–proton transport, enzymatic reactions, and regulatory functions of C₃ photosynthesis has been developed as a system of differential budget equations for intermediate compounds. The emphasis is on electron transport through PSII and PSI and on the modeling of Chl fluorescence and 810 nm absorptance signals. Non-photochemical quenching of PSII excitation is controlled by lumenal pH. Alternative electron transport is modeled as the Mehler type O₂ reduction plus the malate-oxaloacetate shuttle based on the chloroplast malate dehydrogenase. Carbon reduction enzymes are redox-controlled by the ferredoxin–thioredoxin system, sucrose synthesis is controlled by the fructose 2,6-bisphosphate inhibition of cytosolic FBPase, and starch synthesis is controlled by ADP-glucose pyrophosphorylase. Photorespiratory glycolate pathway is included in an integrated way, sufficient to reproduce steady-state rates of photorespiration. Rate-equations are designed on principles of multisubstrate-multiproduct enzyme kinetics. The parameters of the model were adopted from literature or were estimated from fitting the photosynthetic rate and pool sizes to experimental data. The model provided good simulations for steady-state photosynthesis, Chl fluorescence, and 810 nm transmittance signals under varying light, CO₂ and O₂ concentrations, as well as for the transients of post-illumination CO₂ uptake, Chl fluorescence induction and the 810 nm signal. The modeling shows that the present understanding of photosynthesis incorporated in the model is basically correct, but still insufficient to reproduce the dark-light induction of photosynthesis, the time kinetics of non-photochemical quenching, ‘photosynthetic control’ of plastoquinone oxidation, cyclic electron flow around PSI, oscillations in photosynthesis. The model may find application for predicting the results of gene transformations, the analysis of kinetic experimental data, the training of students.     

Role of C3 in humoral immunity. Defective antibody production in C3-deficient dogs

Previous studies have shown that animals pharmacologically depleted of C3 have impaired antibody responses. However, such C depletion is neither complete nor sustained, and the C3 cleavage products generated by C3 depletion can both enhance and inhibit the immune response. To clarify the role of C3 in humoral immunity, the antibody response of dogs with genetically determined total deficiency of C3 (C3D) was examined. Serum IgG levels of the C3D animals were within the normal range, but were significantly lower than levels seen in normal controls or C3D heterozygotes. Specific antibody production was defective: the antibody titers of C3D dogs in response to primary intravenous immunization with two different T cell-dependent Ag (sheep E and bacteriophage phi X-174) were markedly reduced when compared to either normal controls or C3D heterozygotes. After secondary immunization with T-dependent Ag, the total antibody titers were normal, but the C3D dogs made proportionately more IgM and less IgG antibody than did either control group. After i.v. immunization with a T cell-independent Ag (DNP-Ficoll), the C3D dogs had reduced levels of IgM and IgG antibody after primary and secondary immunization. Neither i.m. immunization nor the use of a 20-fold increase in Ag dose i.v. could correct the defect seen in the antibody response of C3D dogs. The results herein demonstrate that C3 plays a critical role in the generation of a normal humoral immune response.     

C3、C4和C3-C4中间型植物的进化

介绍了有关C3、C4和C3-C4中间型植物进化的形态学、生理学、分子生物学、遗传学等方面的证据;推断地球上首先出现C3植物,然后是C3-C4中间类型植物,最后出现C4植物.     

C3 and C6 complement types in schizophrenia

C3 and C6 complement types were studied in schizophrenic patients and controls. The distributions of the three common C3 types (F, FS and S) among the patients was significantly different from that in the controls (p less than 0.005) and the frequency of the C3F gene was significantly increased (p less than 0.0005) among the patients. There were no significant differences in C6 gene or phenotype frequencies between patient and controls.     

Genetic polymorphism of C3 and serum levels of immunoglobulins,C3, C4 components of complement and C3-proactivator in four different populations of Afghanistan

Summary The C3 phenotype distribution was studied in 4 different populations from Afghanistan. The gene frequencies of C3^s allele were: Tajiks (0.8547), Pushtoons (0.8812), Hazaras (0.9036) and Osbeks (0.8530). These values were significantly higher than in European populations studied previously. No significant differences were found between the mean serum levels of C3, C4 and C3-proactivator among 4 population groups. A higher concentration of IgG, IgA and IgM was observed in Afghanistan sera than reported for Europeans.Supported by the Stiftung Volkswagenwerk.Dedicated to Prof. J. Kühnau on his 75th birthday.     

C4-derived soil organic carbon decomposes faster than its C3 counterpart in mixed C3/C4 soils

The large difference in the degree of discrimination of stable carbon isotopes between C3 and C4 plants is widely exploited in global change and carbon cycle research, often with the assumption that carbon retains the carbon isotopic signature of its photosynthetic pathway during later stages of decomposition in soil and sediments. We applied long-term incubation experiments and natural ¹³C-labelling of C3 and C4-derived soil organic carbon (SOC) collected from across major environmental gradients in Australia to elucidate a significant difference in the rate of decomposition of C3- and C4-derived SOC. We find that the active pool of SOC (ASOC) derived from C4 plants decomposes at over twice the rate of the total pool of ASOC. As a result, the proportion of C4 photosynthesis represented in the heterotrophic CO₂ flux from soil must be over twice the proportional representation of C4-derived biomass in SOC. This observation has significant implications for much carbon cycle research that exploits the carbon isotopic difference in these two photosynthetic pathways.     

Downregulation of Complement C3 and C3aR Expression in Subcutaneous Adipose Tissue in Obese Women

Background

The central component of the complement system, C3, is associated with obesity, metabolic syndrome and cardiovascular disease however the underlying reasons are unknown. In the present study we evaluated gene expression of C3, the cleavage product C3a/C3adesArg and its cognate receptor C3aR in subcutaneous and omental adipose tissue in women.

Methods

Women (n = 140, 21–69 years, BMI 19.5–79 kg/m²) were evaluated for anthropometric and blood parameters, and adipose tissue gene expression.

Results

Subjects were separated into groups (n = 34–36) according to obesity: normal/overweight (≤30 kg/m²), obese I (≤45 kg/m²), obese II (≤51 kg/m²), and obese III (≤80 kg/m²). Overall, while omental expression remained unchanged, subcutaneous C3 and C3aR gene expression decreased with increasing adiposity (2-way ANOVA, p<0.01), with a concomitant decrease in SC/OM ratio (p<0.001). In subcutaneous adipose, both C3 and C3aR expression correlated with apoB, and apoA1 and inversely with waist circumference and blood pressure, while C3aR also correlated with glucose (p<0.05–0.0001). While omental C3aR expression did not correlate with any factor, omental C3 correlated with waist circumference, glucose and apoB (all p<0.05). Further, while plasma C3a/C3adesArg increased and adiponectin decreased with increasing BMI, both correlated (C3a negatively and adiponectin positively) with subcutaneous C3 and C3aR expression (p<0.05–0.001) or less).

Conclusions

The obesity-induced down-regulation of complement C3 and C3aR which is specific to subcutaneous adipose tissue, coupled to the strong correlations with multiple anthropometric, plasma and adipokine variables support a potential role for complement in immunometabolism.     

Plasma C3 and C4 Concentrations in Management of Glomerulonephritis

As part of a larger study of serial complement profiles in glomerulonephritis plasma C3 and C4 concentrations were measured using commercially available immunodiffusion plates. A total of 303 samples were obtained from 128 patients suffering from forms of nephritis associated with hypocomplementaemia—namely, lupus nephritis, mesangiocapillary glomerulonephritis (M.C.G.N.), and acute glomerulonephritis.These simple measurements of C3 and C4 gave clinically useful information. In lupus nephritis C3 and C4 generally correlated and C4 concentrations were more often and more profoundly depressed than C3 concentrations. Neither C3 nor C4 concentrations alone correlated well with the antinuclear factor titre.In both acute glomerulonephritis and M.C.G.N. the C3 concentrations were frequently lower than 20% of normal (which was never the case in patients with lupus), while the C4 concentration was usually normal and was almost never depressed in the absence of C3 depression. This suggests activation of complement at the C3 level by the “bypass” pathway in acute nephritis as well as in M.C.G.N., though both may be operating in some patients. In acute glomerulonephritis but not in M.C.G.N. C3 concentrations returned to normal within eight to 12 weeks.The two varieties of M.C.G.N. identified by the site of the deposits in the capillary glomerular walls differed in their C3 levels. In 10 patients with intramembranous dense linear deposits the C3 was always low over very long periods of time, rising in three out of four patients only after transplantation and immunosuppression. Other patients with M.C.G.N., in contrast, often showed normal C3 concentrations. Concentrations of C4 did not differ in either group, being normal in 80% of samples from all types.     

C3植物中C4途径的研究进展

综述了C3植物中C4途径的发现及研究现状;阐述了C3植物中C4途径的几种作用机理;根据C3植物中C4途径的存在,探讨了改造C3植物的遗传特性;并展望了这一领域的研究前景。