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     

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.     

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 variants and disease

The distribution of C3 variants in dermatitis herpetiformis, thyroid cancer, spinal muscular atrophy, multiple sclerosis and psoriasis was studied, and also the Bf phenotype distribution in thyroid cancer. In thyroid cancer there was a significant deficit of heterozygotes for the C3 locus, a possible decrease in the C3F allele frequency and a significant elevation of frequency of the BfF allele. The possible involvement of these alleles in susceptibility to thyroid cancer appears worth further examination.     

Inhibition of lymphocyte blastogenesis by C3c and C3d.

The C3 cleavage products C3c and C3d were tested for their ability to alter the immunoproliferative response of human peripheral mononuclear cells to the antigens SLO and SK-SD, and to the mitogens PHA and PWM. It was found that both C3c (30 to 120 micrograms/ml) and C3d (10 to 40 micrograms/ml) inhibited lymphocyte blastogenesis in the presence on antigens but not mitogens, when cells were cultured in either autologous plasma or FCS. Similarly, the response to antigens of cell populations enriched for T lymphocytes was inhibited, whereas the response to optimal or suboptimal doses of mitogens was unaffected. When nonadherent (NA) cells were reconstituted with increasing numbers of adherent (AD) cells to potentiate the proliferative response of NA cells to the antigen SLO, the addition of either C3c or C3d abolished the potentiation of the response at low levels of reconstitution. However, at given dose of C3c or C3d, addition of excess AD cells could restore the proliferative response. These results suggest that both C3c and C3d can inhibit T cell proliferation in response to antigen and that they may act at the level of the monocyte-T lymphocyte interaction to modulate cellular immune responses.     

Antifungal activity of C3a and C3a-derived peptides against Candida

Antimicrobial peptides are generated during activation of the complement system [Nordahl et al. Proc. Natl. Acad. Sci. U. S. A. 2004, 101:16879-16884]. Here we show that the anaphylatoxin C3a exerts antimicrobial effects against the yeast Candida. Fluorescence microscopy and electron microscopy analysis demonstrated that C3a-derived peptides bound to the cell surface of Candida, and induced membrane perturbations and release of extracellular material. Various Candida isolates were found to induce complement degradation, leading to generation of C3a. Arginine residues were found to be critical for the antifungal and membrane breaking activity of a C3a-derived antimicrobial peptide, CNY21 (C3a; Cys57-Arg77). A CNY21 variant with increased positive net charge displayed enhanced antifungal activity. Thus, C3a-derived peptides can be utilized as templates in the development of peptide-based antifungal therapies.     

Distinct biological activities of C3 and ADP-ribosyltransferase-deficient C3-E174Q

Low-molecular-weight GTP-binding proteins of the Rho family control the organization of the actin cytoskeleton in eukaryotic cells. Dramatic reorganization of the actin cytoskeleton is caused by the C3 exoenzyme derived from Clostridium botulinum (C3), based on ADP-ribosylation of RhoA/B/C. In addition, wild-type as well as ADP-ribosyltransferase-deficient C3-E174Q induce axonal outgrowth of primary murine hippocampal neurons and prevent growth cone collapse, indicating a non-enzymatic mode of action. In this study, we compared the effects of C3-E174Q and wild-type C3 in the murine hippocampal cell line HT22. Treatment of HT22 cells with C3 resulted in Rho ADP-ribosylation and cell rounding. The ADP-ribosyltransferase-deficient mutant C3-E174Q did not induce either Rho ADP-ribosylation or morphological changes. C3 as well as C3-E174Q treatment resulted in growth arrest, reduced expression of cyclin?D levels, and increased expression of RhoB, a negative regulator of cell-cycle progression. Serum starvation induced apoptosis in HT22 cells, as determined on the basis of increased expression of caspase-9 and Bax. C3 but not C3-E174Q protected serum-starved HT22 cells from apoptosis. This is the first study separating ADP-ribosyltransferase-dependent from ADP-ribosyltransferase-independent effects of C3. While morphological changes and anti-apoptotic activity strictly depend on ADP-ribosyltransferase activity, the anti-proliferative effects are independent of ADP-ribosyltransferase activity.     

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.     

Insect herbivory on C3 and C4 grasses

Summary This study tested the hypothesis that grasses with the C₄ photosynthetic pathway are avoided as a food source by insect herbivores in natural communities. Insects were sampled from ten pairs of C₃–C₄ grasses and their distributions analyzed by paired comparisons tests. Results showed no statistically significant differences in herbivore utilization of C₃–C₄ species. However, there was a trend towards heavier utilization of C₃ species when means for both plant groups were compared. In particular, Homoptera and Diptera showed heavier usage of C₃ plants. Significant correlations between insect abundances and plant protein levels suggest that herbivores respond to the higher protein content of C₃ grasses. ¹³C values for six of the most common grasshopper species in the study area indicated that three species fed on C₃ plants, two species fed on C₄ plants, and one species consumed a mixture of C₃ and C₄ tissue.Welder Wildlife Refuge Contribution Number 213     

Phosphorus responses of C3 and C4 species

An hypothesis was formulated that phosphorus (P) partitioningin tissues of C₄ leaves would permit C₄ plants to resist P deficiencybetter than C₃ plants. To test this hypothesis, 12 C₃, C₄, andC₃–C₄ intermediate species were grown at adequate, deficient,and severely deficient P supply in a solid-phase-buffered sandculture system to characterize photosynthetic and growth responses.Species differed considerably in response to P stress. The growthof C₃ species was more sensitive to P supply than C₄ species,but C₃ and C₄ species had similar photosynthetic P use efficiency,and C₄ species did not have low leaf P content, contrary toour hypothesis. In fact, leaf photosynthetic rates were notcorrelated with growth responses. Moncots had lower leaf P contentand better maintenance of leaf production under P stress thandicots, because of greater inhibition of branching (dicots)than of tillering (monocots). The most P efficient species inthis survey was Brachiaria, a C₄ monocot that increased rootbiomass allocation under stress while maintaining P allocationto the shoot. It is concluded that C₄ species are not inherentlymore P efficient than C₃ species, but that monocots are moreP efficient than dicots, because of contrasting P and biomassallocation under stress. Key words: Phosphorus deficiency, C₃ plants, C₄ plants, growth response     

Physiologic inactivation of fluid phase C3b: isolation and structural analysis of C3c, C3d,g (alpha 2D), and C3g

The fragments that result from the inactivation of C3b have not been completely characterized. Initial inactivation is catalyzed by the protease factor I, which, in the presence of its cofactor (factor H), cleaves two peptide bonds in the alpha'-chain of C3b. This results in the release of a small peptide (C3f, Mr 3000) from iC3b, which consists of the C3 beta chain covalently bonded to two alpha'-chain-derived peptides (Mr 68,000 and Mr 43,000). Surface-bound iC3b is cleaved at a third site by factor I to produce C3c and C3d,g (or alpha 2D). The factor I cofactor for this cleavage is the C3b receptor that is present on erythrocyte and leukocyte membranes. This report describes the isolation and initial structural characterization of C3c and C3d,g generated in whole blood after complement activation with cobra venom factor. These fragments were compared with the C3 fragments isolated from the serum and plasma of a patient with complement activation in vivo. The fragments were isolated with two solid phase monoclonal antibodies, one of which recognizes a determinant on C3g (clone 9) and one of which recognizes a determinant on C3c (clone 4). C3c isolated from normal blood showed three polypeptides that had apparent m.w. of 75,000, 43,000, and 27,000. The C3d,g consisted of a single polypeptide chain with a m.w. of 40,000. Amino terminal sequence analysis showed that the Mr 27,000 peptide from C3c is derived from the amino terminal portion of the alpha'-chain of C3b, whereas the Mr 43,000 peptide is derived from the carboxy terminus of the same chain. Amino terminal sequence analysis showed also that C3g is derived from the amino terminus of C3d,g. The C3 fragments isolated from a patient with partial lipodystrophy, nephritic factor activity, low serum C3 levels, and circulating C3 cleavage products showed a more complicated pattern on SDS-PAGE. The fragment isolated with clone 9 had an apparent m.w. of 40,000, identical to C3d,g generated in vitro, and it had the same amino terminal sequence as C3d,g generated in vitro. The eluate from insolubilized clone 4, however, showed prominent bands with Mr of 75,000, 56,000, 43,000, and 27,000, together with a triple-banded pattern at 68,000 and a minor band at 80,000. This eluate thus appears to contain C3c, and iC3b or an iC3b-like product. The origin of the Mr 56,000 and Mr 80,000 peptides have not yet been determined. These studies, with previous data, definitively order the C3c and C3d,g peptides in the alpha-chain of C3.(ABSTRACT TRUNCATED AT 400 WORDS)     

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.     

Light-dependent net CO-evolution by C3 and C4 plants

Light-dependent CO-evolution by the green leaves of C₃ and C₄ plants depends on the CO₂/O₂ ratio in the ambient atmosphere. This and other physiological responses suggest that CO-evolution is a byproduct of photorespiration. At CO₂/O₂ ratios up to 10^-3, the ratio of CO evolved: CO₂ fixed in photosynthesis is significantly higher in C₃ than in C₄ plants. This discrepancy disappears when a correction is made for the CO₂-concentrating mechanism in C₄ photosynthesis, by which CO₂-concentration at the site of ribulose-bis-phosphate carboxylase/oxygenase in the bundle sheaths is raised significantly as compared to the ambient atmosphere. Since the oxygenase function of this enzyme is responsible for glycolate synthesis, i.e., the substrate of photorespiration, this result seems to support the conclusion that CO-evolution is a consequence of photorespiration. CO-evolution may turn out to be a useful and rather straightforward indicator for photorespiration in ecophysiological studies.Abbreviations CAM crassulacean acid metabolism - CO net CO-evolution - CO₂ net CO₂-fixation - PEP-C phosphoenolpyruvate carboxylase - RubP-C ribulose-bisphosphate carboxylase/oxygenase Dedicated to Professor André Pirson on the occasion of his 70th birthday     

C3, BF and C4 polymorphisms in Tunisians

The C3, BF, C4A and C4B polymorphisms were studied in a Tunisian population sample. The allelic frequencies for C3 were S = 0.844 and F = 0.148, and for BF, S = 0.535, F = 0.331, SO7 = 0.075 and F1 = 0.041. The most frequent C4 alleles were A3 and B1 followed in a decreasing order by A2, B2 and the A and B null alleles. The results indicate that the Tunisian population is intermediate between the Caucasian and Arab populations with some trace admixture of African Blacks.