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1.
Elevated CO2 (ambient + 35 Pa) increased shoot dry mass production in Avena fatua by 68% at maturity. This increase in shoot biomass was paralleled by an 81% increase in average net CO2 uptake (A) per unit of leaf area and a 65% increase in average A at the ecosystem level per unit of ground area. Elevated CO2 also increased ecosystem A per unit of biomass. However, the products of total leaf area and light-saturated leaf A divided by the ground surface area over time appeared to lie on a single response curve for both CO2 treatments. The approximate slope of the response suggests that the integrated light saturated capacity for leaf photosynthesis is 10-fold greater than the ecosystem rate. Ecosystem respiration (night) per unit of ground area, which includes soil and plant respiration, ranged from-20 (at day 19) to-18 (at day 40) mol m-2 s-1 for both elevated and ambient CO2
Avena. Ecosystem below-ground respiration at the time of seedling emergence was -10 mol m-2 s-1, while that occuring after shoot removal at the termination of the experiment ranged from -5 to-6 mol m-2 s-1. Hence, no significant differences between elevated and ambient CO2 treatments were found in any respiration measure on a ground area basis, though ecosystem respiration on a shoot biomass basis was clearly reduced by elevated CO2. Significant differences existed between leaf and ecosystem water flux. In general, leaf transpiration (E) decreased over the course of the experiment, possibly in response to leaf aging, while ecosystem rates of evapotranspiration (ET) remained constant, probably because falling leaf rates were offset by an increasing total leaf biomass. Transpiration was lower in plants grown at elevated CO2, though variation was high because of variability in leaf age and ambient light conditions and differences were not significant. In contrast, ecosystem evapotranspiration (ET) was significantly decreased by elevated CO2 on 5 out of 8 measurement dates. Photosynthetic water use efficiencies (A/E at the leaf level, A/ET at the ecosystem level) were increased by elevated CO2. Increases were due to both increased A at leaf and ecosystem level and decreased leaf E and ecosystem ET. 相似文献
2.
Timothy P. Jones Steven M. Fortier Allan Pentecost Margaret E. Collinson 《Biogeochemistry》1996,34(2):99-112
Charophyte oosporangia and water samples from a highly calcareous lake were measured for stable carbon and oxygen isotopic composition. The time period over which the oosporangia calcify is short, thus any biochemical relationship between the water and oosporangia"s calcite represents only one time window (late Summer in Malham Tam). This important temporal restraint must also apply to interpretations of all fossil material measured. The 18Oc of the charophyte oosporangia is deduced to be in equilibrium with the 18O of the water for a given temperature. The 13 Cc of the charophyte oosporangia was approximately 2.5 per mil lower than the 13CDIC in the water we measured. With the release Of CO2 with phosphoric acid from the charophyte oosporangia, there was no significant difference in the 18Oc values obtained, regardless of whether or not the carbonate was separated from the organic center, however 13Cc values were marginally lower for carbonate plus organic center measurements. Our results indicate that fossil charophyte gyrogonites can be used to elucidate the geochemistry of the ancient water body in which they lived. 相似文献
3.
Carbon-isotope ratios were examined as 13C values in several C3, C4, and C3–C4
Flaveria species, and compared to predicted 13C, values generated from theoretical models. The measured 13C values were within 4 of those predicted from the models. The models were used to identify factors that contribute to C3-like 13C values in C3–C4 species that exhibit considerable C4-cycle activity. Two of the factors contributing to C3-like 13C values are high CO2 leakiness from the C4 pathway and pi/pa values that were higher than C4 congeners. A marked break occurred in the relationship between the percentage of atmospheric CO2 assimilated through the C4 cycle and the 13C value. Below 50% C4-cycle assimialtion there was no significant relationship between the variables, but above 50% the 13C values became less negative. These results demonstrate that the level of C4-cycle expression can increase from, 0 to 50% with little integration of carbon transfer from the C4 to the C3 cycle. As expression increaces above 50%, however, increased integration of C3- and C4-cycle co-function occurs.Abbreviations and symbols RuBP carboxylase
ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39)
- PEP carboxylase
phosphoenolpyruvate carboxylase (EC 4.1.1.31)
- pa
atmospheric CO2 partial pressure
- pi
intercellular CO2 partial pressure
-
isotope ratio
-
quantum yield for CO2 uptake 相似文献
4.
Summary Crassulacean acid metabolism (CAM) was studied in a tropical epiphytic fern, Pyrrosia longifolia, from a fully sun-exposed and from a very shaded site in Northern Queensland, Australia. Measurements of instantaneous net CO2 exchange showed carbon gain via CO2 dark fixation with some net CO2 uptake also occuring during late afternoon, in both sun and shade fronds. Maximum rates of net CO2 uptake and the nocturnal increase in titratable acidity were lower in shade than in sun fronds. 13C values of sun and shade fronds were not significantly different, and ranged between-14 and-15 suggesting that, in the long term, carbon gain was mainly via CO2 dark fixation. Sun fronds had a higher light compensation point of photosynthesis than shade fronds but the same quantum yield. Yet there was no acclimation of photosynthetic O2 evolution, (measured at 5% CO2) in sun and shade fronds and photosynthesis saturated at between 200 and 400 mol quanta m-2 s-1. Use of higher light intensities for photosynthesis of sun fronds was probably precluded by low nutrient availability. Total nitrogen was less than 1% of dry weight in fully expanded sun and shade fronds. Exposure of shade fronds to full sunlight for 6 h led to a 60% decline in the quantum yield of photosynthesis and to a decline in variable fluorescence measured at room temperature. Photoinhibition by high light was also observed in Hoya nicholsoniae, a rainforest climber growing in deep shade. This species also exhibited CAM as demonstrated by nocturnal net CO2 uptake, nocturnal acidification and a 13C value of-14. Photosynthetic O2 evolution in this species was saturated at 2.5% of full sunlight. Two species of Dendrobium (Orchidaceae) from sun-exposed sites, one species exhibiting CAM and the other one exhibiting net CO2 uptake exclusively during daytime via conventional C3 photosynthesis, showed similar light response curves and the same quantum yield for photosynthetic O2 evolution. 相似文献
5.
Paul Teese 《Oecologia》1995,102(3):371-376
CO2 compenstation point (), the concentration of CO2 at which photosynthesis and respiration are at equilibrium, is a commonly used diagnostic for the C4 photosynthetic pathway, since it reflects the reduced photorespiration that is a property of C4 photosynthesis. Geographic variation for was examined within Flaveria linearis, a C3–C4 intermediate species. Collections from four widely separated Floridian populations were propagated in a greenhouse and measured for . Little differentiation among populations was found, but significant within-population variation was present. Temperature is a hypothesized selective agent for the C4 photosynthetic pathway. To test this hypothesis, plants exhibiting a range of were cloned and placed in growth chambers at 25°C and 40°C. After 7 weeks, valves were remeasured and plants were harvested and weighed. There was a poor correlation between initial and final measures of for a given genotype (r=0.38, P>0.1). Broad sense heritability for was computed to be 0.10. At 25°C, there was no relationship between final size and . At 40°C, more C4-like plants, as indicated by their low , had grown larger. Differences in relative growth rate were attributable more to differences in net assimilation rate than in leaf area ratio. Taken together, these results demonstrate that although significant plasticity exists in the amount of photorespiration in this C3–C4 species, high temperature appears to be an effective selective agent for the reduction of photorespiration and the enhancement of C4-like traits. 相似文献
6.
A. M. Borland H. Griffiths M. S. J. Broadmeadow M. C. Fordham C. Maxwell 《Oecologia》1993,95(3):444-453
On-line instantaneous carbon isotope discrimination was measured in conjunction with net uptake of CO2 in leaves of exposed and shaded plants of the C3-CAM intermediate Clusia minor growing under natural conditions in Trinidad. At the end of the rainy season (late January-early February, 1992) C3 photosynthesis predominated although exposed leaves recaptured a small proportion of respiratory CO2 at night for the synthesis of malic acid. Citric acid was the major organic acid accumulated by exposed leaves at this time with a citric: malic acid ratio of 11:1. Values of instantaneous discrimination () in exposed leaves during the wet season rose from 17.1 shortly after dawn to 22.7 around mid-day just before stomata closed, suggesting that most CO2 was fixed by Rubisco at this time. During the late afternoon, instantaneous declined from 22.2 to 17, probably reflecting the limited contribution from PEPc activity and an increase in diffusional resistance to CO2 in exposed leaves. Shaded leaves showed no CAM activity and CO2 uptake proceeded throughout the day in the wet season. The decrease in instantaneous from 27 in the morning to 19.2 in the late afternoon was therefore entirely due to diffusional limitation. Leaves sampled in the dry season (mid-March, 1992) had by now induced full CAM activity with both malic and citric acids accumulated overnight and stomata closed for 4–5 h over the middle of the day. Values of instantaneous measured over the first 3 h after dawn (6.4–9.1) indicated that C4 carboxylation dominated CO2 uptake for most of the morning when rates of photosynthesis were maximal, implying that under natural conditions, the down regulation of PEPc in phase II occurs much more slowly than laboratory-based studies have suggested. The contribution from C3 carboxylation to CO2 uptake during phase II was most marked in leaves which accumulated lower quantities of organic acids overnight. In exposed leaves, measurements of instantaneous during the late afternoon illustrated the transition from C3 to C4 carboxylation with stomata remaining open during the transition from dusk into the dark period. Uptake of CO2 by shaded leaves during the late afternoon however appeared to be predominantly limited by decreased stomatal conductance. The short-term measurements of instantaneous were subsequently integrated over 24 h in order to predict the leaf carbon isotope ratios (p) and to compare this with the p measured for leaf organic material. Whilst there was close agreement between predicted and measured p for plants sampled in the wet season, during the dry season the predicted carbon isotope ratios were 5–9 higher than the measured isotope ratios. During the annual cycle of leaf growth most carbon was fixed via the C3 pathway although CAM clearly plays an important role in maintaining photochemical integrity in the dry season. 相似文献
7.
Chlorobium limicola has been proposed to assimilate CO2 autotrophically via a reductive tricarboxylic acid cycle rather than via the Calvin cycle. This proposal has been a matter of considerable controversy. In order to determine which pathway is operative, the bacterium was grown on a mineral salts medium with CO2 as the main carbon source supplemented with specifically labeled 14C-pyruvate, and the incorporation of 14C into alanine (intracellular pyruvate), aspartate (oxaloacetate), glutamate (-ketoglutarate), and glucose (hexosephosphate) was measured in exponentially growing cells in long term labeling experiments. During growth in presence of pyruvate, 20% of the cell carbon were derived from pyruvate in the medium, 80% from CO2. Since pyruvate was not oxidized to CO2, only those compounds should become labeled which were synthesized from CO2 via pyruvate.The three amino acids and glucose were found to be labeled. Alanine had one fifth the specific radioactivity of the extracellular pyruvate, indicating that 20% of the intracellular pyruvate pool were derived from pyruvate in the medium, 80% were synthesized from CO2. Glucose had twice the specific radioactivity of alanine, showing that hexosephosphate synthesis from CO2 proceeded via the pyruvate pool. The latter finding is not consistent with the operation of the Calvin cycle, in which pyruvate is not an intermediate. The specific radioactivities of aspartate (oxaloacetate) and of glutamate (-ketoglutarate) were practically identical but considerably lower than that of alanine ( intracellular pyruvate). These findings are compatible with the operation of a reductive tricarboxylic acid cycle as mechanism of autotrophic CO2 fixation. Degradation studies of the cell components support this interpretation.
Offprint requests to: G. Fuchs 相似文献
8.
Rajendra Prasad Roy Parimala Nacharaju Ronald L. Nagel A. Seetharama Acharya 《Journal of Protein Chemistry》1995,14(2):81-88
Interspecies hybrids of HbA and Hb from mouse C57BL/10 [
2
M
2
H
and
2
H
2
M
(H=human, M=mouse)], representing 19 and 27 sequence differences per dimers (as compared with human dimer) have been generatedin vitro. The efficiency of the assembly of the interspecies hybrids by the alloplex intermediate pathway is about twofold higher than the low-pH-mediated subunit approach. The interspecies hybrids exhibit a cooperative O2 binding. The intrinsic O2 affinity of mouse Hb is slightly lower than HbA, while the 2,3-diphosphoglycerate (DPG) effect is comparable. Interestingly, the interspecies hybrid
2
M
2
H
has high O2 affinity (compared to either human or mouse Hb), while the interspecies hybrid
2
H
2
M
exhibits a very low O2 affinity. These results suggest that the mouse chain generates a tetramer with very low oxygen affinity. However, the complementarity of the mouse and chains generates a set of unique interactions that compensate for the low-oxygen-affinity propensity of the mouse chain. DPG binds the tetramer in the central cavity formed by the two subunits, hence the DPG effects on the interspecies hybrids should be as in the parent molecule. However, the results of the present study demonstrate that the DPG binding pocket is influenced by the nature of the chain present in the tetramer. The mouse chain reduces considerably the DPG right shift of the O2 affinity of the human-chain containing hybrid. Sequence analysis suggest that perturbations of the
1
1 (not the
1
2) are communicated to the DPG binding pocket in the presence of the alien subunit, and are the primary determinant of the ligand binding properties. The results have implications for the design of Hb-based blood substitutes and understanding of the inhibitory potential of mouse chains in transgenic mouse expressing human
S chains. 相似文献
9.
Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies
In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m-2 s-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m-2 s-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO2 response. At PPFD-saturation CE was 0.018 mol m-2 s-1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO2 was 0.05–0.08 mol/mol.
and PPFD-saturated CO2 exchange was 6–8 mol m-2 s-1. The ratio of internal CO2 concentration to external (C
i
/C
a
) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C
i
/C
a
during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO2 exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols
A
measured photosynthetic rate under any set of conditions (mol m-2 s-1)
-
A
m
(atm)
measured photosynthetic rate at saturating PPFD, 350 l/l CO2 and 21% (v/v) O2 (mol m-2 s-1)
-
C
constant in equation of Smith (1937, 1938)
-
C
a
CO2 concentration in the air (l/l)
-
C
i
CO2 concentration in the intercellular air space (l/l)
-
C
i
/*
C
i
corrected for CO2 compensation point, i.e., C
i
-I
*, (l/l)
- CE
initial slope of the CO2 response of photosynthesis (mol m-2 s-1/(l/l))
- CEM
CE at PPFD saturation
-
E
transpiration rate (mmol m-2 s-1)
-
F
predicted photosynthetic rate (mol m-2 s-1)
-
G
leaf conductance to H2O (mol m-2 s-1)
-
I
photosynthetic photon flux density (mol m-2 s-1)
-
N
number of data points
-
P
m
predicted photosynthetic rate at saturating CO2 and given PPFD (mol m-2 s-1)
-
P
ml
predicted photosynthetic rate at saturating CO2 and PPFD (mol m-2 s-1)
-
R
d
residual respiratory rate (mol m-2 s-1)
-
T
a
air temperature (°C)
-
T
l
leaf temperature (°C)
-
V
reaction velocity in equation of Smith (1937, 1938)
-
V
max
saturated reaction velocity in equation of Smith (1937, 1938)
- VPA
vapor pressure of water in the air (mbar/bar)
- VPD
vapor pressure difference between leaf and air (mbar/bar)
-
X
substrate concentration in equation of Smith (1937, 1938)
-
initial slope of the PPFD response of photosynthesis at saturating CO2 (mol CO2/mol quanta)
- (atm)
initial slope of the PPFD response of photosynthesis at 340 l/l CO2 and 21% (v/v) O2 (mol CO2/mol quanta)
-
I
*
CO2 compensation point after correction for residual respiration (l/l)
-
PPFD compensation point (mol m-2 s-1) 相似文献
10.
Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO2 enrichment up to 6000 l CO2 l–1. This high CO2 optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO2 was less or absent following four days growth in 2% O2. The Leaf Area Ratio decreased in response to CO2 enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO2 enrichment up to 1500 l CO2 l–1 during measurement, showing only small increases with further CO2 enrichment up to 5000 l CO2 l–1 at a photon flux density of 210 mol m–2 s–1 and small decreases at 2000 mol m–1 s–1. The actual rate of photosynthesis of those plants cultivated at high CO2 levels, however, was less than the air grown plants. The response of photosynthesis to O2 indicated that the enhancement of growth and photosynthesis by CO2 enrichment was a result of decreased photorespiration. Plants cultivated in low O2 produced abnormal morphological features and after a short time showed a reduction in growth. 相似文献
11.
Fumiaki Nakatsubo T. Kent Kirk Mikio Shimada Takayoshi Higuchi 《Archives of microbiology》1981,128(4):416-420
The degradation of the phenylcoumaran substructure model compound methyl dehydrodiconiferyl alcohol by the white-rot wood decay fungus Phanerochaete chrysosporium was investigated using culture conditions optimized for lignin oxidation. Initial attack was in the cinnamyl alcohol side chain, which was oxidized to a glycerol structure. This was subsequently converted by loss of the two terminal carbon atoms, C and C, to yield a C-aldehyde structure, which was further oxidized to the C-acid compound. The next detected intermediate, a phenylcoumarone, was produced by double bond formation between C and C, and oxidation of the C-alcohol to an aldehyde group. Further oxidation of C to an acid yielded the next intermediate. The final identified degradation product was veratric acid. No products from the 5-substituted aromatic ring, and no phenolic products, were found. The initial glycerol-containing intermediate was a mixture of the threo and erythro forms, and no optical activity could be found, suggesting that its formation might have involved nonstereospecific C-C epoxidation followed by non-enzymatic hydrolysis of the epoxide.Abbreviations TLC
thin layer chromatography
- LDA
lithium diisopropyl amide
- DDQ
2,3-dichloro-5,6-dicyanobenzoquinone
- MS
mass spectrometry
- UV
ultraviolet spectroscopy 相似文献
12.
Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon 总被引:2,自引:1,他引:1
Andrea Viviana Waichman 《Hydrobiologia》1996,341(1):27-36
The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (13C) were used as tracers. Values of 13C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO2.The percentage of carbon derived from C4 macrophytes for bacterially produced CO2 was the highest, on average 89%. The average 13C value of CO2 from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO2 of 3 by bacterial respiration, 13C value was –15.5, near C4 macrophyte 13C value (–13.1).The average value of total DOC 13C was –26.8 ± 2.4. The percentage of C4 macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C3 plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C4 macrophytes to the consumers. 相似文献
13.
The carbon isotope composition of an animals breath reveals the composition of the nutrients that it catabolizes for energy. Here we describe the use of Keeling plots, a method widely applied in ecosystem ecology, to measure the 13C of respired CO2 of small vertebrates. We measured the 13C of Rufous Hummingbirds (Selasphorus rufus) in the laboratory and of Mourning (Zenaida macroura) and White-winged (Z. asiatica) Doves in the field. In the laboratory, when hummingbirds were fed a sucrose based C3 diet, the 13C of respired CO2 was not significantly different from that of their diet (13CC3 diet). The 13C of respired CO2 for C3 fasted birds was slightly, albeit significantly, depleted in 13C relative to 13CC3 diet. Six hours after birds were shifted to a sucrose based C4 diet, the isotopic composition of their breath revealed that birds were catabolizing a mixture of nutrients derived from both the C3 and the C4 diet. In the field, the 13C of respired CO2 from Mourning and White-winged Doves reflected that of their diets: the CAM saguaro cactus (Carnegeia gigantea) and C3 seeds, respectively. Keeling plots are an easy, effective and inexpensive method to measure 13C of respired CO2 in the lab and the field. 相似文献
14.
The conformational properties of the oligosaccharide chain of GM1 ganglioside containingN-glycolyl-neuraminic acid, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer, were studied through NMR nuclear Overhauser effect investigations on the monomeric ganglioside in dimethylsulfoxide, and on mixed micelles of ganglioside and dodecylphosphocholine in water. Several interresidual contacts for the trisaccharide core--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-were found to fix the relative orientitation of the three saccharides, while the glycosidic linkage of the terminal -Gal-was found to be quite mobile as the -Gal-(1-3)--GalNAc-disaccharide exists in different conformations. These results are similar to those found for two GM1 gangliosides containingN-acetyl-neuraminic acid and neuraminic acid [1].Abbreviations Ganglioside nomenclature is in accordance with Svennerholm [23] and the IUPAC-IUB Recommendations [24] GM3(Neu5Ac)
II3Neu5AcLacCer, -Neu5Ac-(2-3)--Gal-(1-4)--Glc-(1-1)-Cer
- GM3(Neu5Gc)
II3Neu5GcLacCer, -Neu5Gc-(2-3)--Gal-(1-4)--Glc-(1-1)-Cer
- GM1(Neu5Ac)
II3Neu5AcGgOse4Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer
- GM1(Neu5Gc)
II3Neu5GcGgOse4Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer
- GM1(Neu)
II3NeuGgOse4Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu-(2-3)]--Glc-(1-1)-Cer
- GD1a
IV3Neu5AcII3Neu5AcGgOse4Cer, -Neu5Ac-(2-3)--Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer
- GalNAc-GD1a
IV4GalNAcIV3Neu5AcII3Neu5AcGgOse4Cer, -GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer
- Neu
neuraminic acid
- Neu5Ac
N-acetyl-neuraminic acid
- Neu5Gc
N-glycolyl-neuraminic acid
- Cer
ceramide 相似文献
15.
Particulate membrane preparations have been isolated from cambial cells, and from differentiating and differentiated xylem cells of the main stem of pine trees. These preparations synthesise a 14 glucomannan from guanosine 5-diphosphate-mannose. The polysaccharide and the synthase have been characterized and the Km and Vmax for the synthase determined as 85 M and 52.9 M·min-1, respectively. The enzymic activity was inhibited by the addition of guanosine 5-diphosphate-D-glucose so that the presence of an epimerase on the particulate fraction in conjunction with the synthase probably allowed the heteropolymer to be formed with the optimal ratio of the concentrations of the nucleoside-diphosphate sugar donors. No evidence for a polyprenyl-phosphate derivative as an intermediate during the polymer synthesis was obtained. Part of the control mechanism for the deposition of the large amounts of the glucomannan during the secondary thickening of the tracheids of the vascular system is by an increase in the amount of synthase activity at the endomembrane system of the cells. This probably occurs by an increase in the amount of enzyme which is modulated by gene regulation during differentiation.Abbreviations GDP
guanosine 5-diphosphate
- GLC
gasliquid chromatography 相似文献
16.
Both qualitative and quantitative differences in the minor nucleotide constituents of rRNA from normally grown and from etiolated wheat plants (Triticum aestivum L.) were established. Using different degradation methods and separation techniques the 18S+26S RNA of 8-day-old wheat seedlings grown in the light was found to contain 5-methylcytidine, 3-methylcytidine, 5-methyluridine, 3-methyluridine, 5-carboxymethyluridine, 1-methyladenine, N-methyladenine, 5-hydroxymethylcytidine, O2-methyluridine, O2-methylcytidine, pseudouridine, O2-methylpseudouridine, N2,N2-dimethylguanine, 1-methylguanine, ribothymidine and some unknown minor constituents. On the other hand, there were only a few minor nucleotides in the rRNA of etiolated wheat seedlings. Cycloheximide, a cytoplasmic protein synthesis inhibitor, simulated etiolation in that it reduced the number of minor nucleotides in rRNA, whereas chloramphenicol, a chloroplast protein synthesis inhibitor, had no significant effect on the minor nucleotide content of rRNA. This finding suggests that illumination may cause de novo synthesis of cytoplasmic modifying enzymes leading to the formation of highly modified rRNAs.Abbreviations m6A
N6-methyladenine
- m1A
1-methyladenine
- 5hmc
5-hydroxymethylcytidine
- Cm
O2-methylcytidine
- m5C
5-methylcytidine
- m3C
3-methylcytidine
- m1G
1-methylguanine
- m
2
2
G
N2, N2-dimethylguanine
-
pseudouridine
- m
O2-methylpseudouridine
- Um
O2-methyluridine
- m3U
3-methyluridine
- m5U
5-methyluridine
- cm5U
5-carboxymethyluridine
- rT
ribothymidine
- Pur
purine
- Pyr
pyrimidine
- RNase
ribonuclease
- UV
ultra violet
- p
phosphate 相似文献
17.
Rotational diffusion properties have been derived for the DNA dodecamer d(CGCGAATTCGCG)2 from 13C R1 and R1 measurements on the C1, C3, and C4 carbons in samples uniformly enriched in 13C. The narrow range of C-H bond vector orientations relative to the DNA axis make the analysis particularly sensitive to small structural deviations. As a result, the R1/R1 ratios are found to fit poorly to the crystal structures of this dodecamer, but well to a recent solution NMR structure, determined in liquid crystalline media, even though globally the structures are quite similar. A fit of the R1/R1 ratios to the solution structure is optimal for an axially symmetric rotational diffusion model, with a diffusion anisotropy, D||/D, of 2.1±0.4, and an overall rotational correlation time, (2D||+4D)–1, of 3.35 ns at 35 °C in D2O, in excellent agreement with values obtained from hydrodynamic modeling. 相似文献
18.
P. E. Cheshev E. A. Khatuntseva Yu. E. Tsvetkov A. S. Shashkov N. E. Nifantiev 《Russian Journal of Bioorganic Chemistry》2004,30(1):60-70
4-O-Glycosylation of 2-azidoethyl 2,3,6-tri-O-benzyl-4-O-(2,3-di-O-benzyl-6-O-benzoyl--D-galactopyranosyl)--D-glucopyranoside with a disaccharide donor, 4-trichloroacetamidophenyl 4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl--D-galactopyranosyl)-1-thio-2-trichloroacetamido--D-galactopyranoside, in dichloromethane in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid resulted in a tetrasaccharide, 2-azidoethyl (2,3,4,6-tetra-O-acetyl--D-galactopyranosyl)-(1 3)-(4,6-di-O-acetyl-2-deoxy-2-trichloroacetamido--D-galactopyranosyl)-(1 4)-(2,3-di-O-benzyl-6-O-benzoyl--D-galactopyranosyl)-(1 4)-2,3,6-tri-O-benzyl--D-glucopyranoside, in 69% yield. The complete removal of O-protecting groups in the tetrasaccharide, the replacement of N-trichloroacetyl by N-acetyl group, and the reduction of the aglycone azide group to amine led to the target aminoethyl glycoside of -D-Gal-(1 3)--D-GalNAc-(1 4)--D-Gal-(1 4)--D-Glc-OCH2CH2NH2 containing the oligosaccharide chain of asialo-GM1 ganglioside in 72% overall yield. Selective 3-O-glycosylation of 2-azidoethyl 2,3,6-tri-O-benzyl-4-O-(2,6-di-O-benzyl--D-galactopyranosyl)--D-glucopyranoside with thioglycoside methyl (ethyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero--D-galacto-2-nonulopyranosyl)oate in acetonitrile in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid afforded 2-azidoethyl [methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero--D-galacto-2-nonulopyranosyl)oate]-(2 3)-(2,6-di-O-benzyl--D-galactopyranosyl)-(1 4)-2,3,6-tri-O-benzyl--D-glucopyranoside, the selectively protected derivative of the oligosaccharide chain of GM3 ganglioside, in 79% yield. Its 4-O-glycosylation with a disaccharide glycosyl donor, (4-trichloroacetophenyl-4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl--D-galactopyranosyl) 1-thio-2-trichloroacetamido--D-galactopyranoside in dichloromethane in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid gave 2-azidoethyl (2,3,4,6-tetra-O-acetyl--D-galactopyranosyl)-(1 3)-(4,6-di-O-acetyl-2-deoxy-2-trichloroacetamido--D-galactopyranosyl)-(1 4)-{[methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero--D-galacto-2-nonulopyranosyl)onate]-(2 3)}-(2,6-di-O-benzyl--D-galactopyranosyl)-(1 4)-2,3,6-tri-O-benzyl--D-glucopyranoside in 85% yield. The resulting pentasaccharide was O-deprotected, its N-trichloroacetyl group was replaced by N-acetyl group, and the aglycone azide group was reduced to afford in 85% overall yield aminoethyl glycoside of -D-Gal-(1 3)--D-GalNAc-(1 4)-[-D-Neu5Ac-(2 3)]--D-Gal-(1 4)--D-Glc-OCH2CH2NH2 containing the oligosaccharide chain of GM1 ganglioside. 相似文献
19.
A chimeric stilbene synthase (sts)gene was transferred into wheat. Stilbene synthases play a role in the defence against fungal diseases in some plant species (e.g. groundnut or grapevine) by producing stilbenetype phytoalexins like resveratrol. Resveratrol is also claimed to have positive effects to human health. Embryogenic scutellar calli derived from immature embryos of the two commercial German spring wheat cultivars Combi and Hanno were used as target tissue for cotransformation by microprojectile delivery. The selectable marker/reporter gene constructs contained the bargene either driven by the ubiquitinpromoter from maize (pAHC 25, also containing the uidAgene driven by the ubiquitinpromoter), or by the actinpromoter (pDM 302) from rice. The cotransferred plasmid pStil 2 consisted of a grapevine stscoding region driven by the ubiquitin promoter. Eight transgenic Combi and one Hanno TOplant were obtained and, except one Combi TOplant, found to be cotransformants due to the integration of both the stsgene and the selectable marker or reporter genes. Expression of the stsgene was proven by RTPCR, and, for the first time, by detection of the stilbene synthase product resveratrol by HPLC and mass spectrometry. The stsgene was expressed in four of the seven transgenic Combi T_oplants. Two of the respective T1progenies segregated in a Mendelian manner were still expressing the gene. Investigations into methylation of the stsgene showed that in three nonexpressing progenies inactivation was paralleled by methylation. 相似文献
20.
Folkert Reck Ernst Meinjohanns Matthias Springer Roland Wilkens Johannes A. L. M. Van Dorst Hans Paulsen Gabriele Möller Inka Brockhausen Harry Schachter 《Glycoconjugate journal》1994,11(3):210-216
UDP-GlcNAc: Man1-6R (1-2)-N-acetylglucosaminyltransferase II (GlcNAc-T II; EC 2.4.1.143) is a key enzyme in the synthesis of complexN-glycans. We have tested a series of synthetic analogues of the substrate Man1-6(GlcNAc1-2Man1-3)Man-O-octyl as substrates and inhibitors for rat liver GlcNAc-T II. The enzyme attachesN-acetylglucosamine in 1-2 linkage to the 2-OH of the Man1-6 residue. The 2-deoxy analogue is a competitive inhibitor (K
i=0.13mm). The 2-O-methyl compound does not bind to the enzyme presumably due to steric hindrance. The 3-, 4- and 6-OH groups are not essential for binding or catalysis since the 3-, 4- and 6-deoxy and -O-methyl derivatives are all good substrates. Increasing the size of the substituent at the 3-position to pentyl and substituted pentyl groups causes competitive inhibition (K
i=1.0–2.5mm). We have taken advantage of this effect to synthesize two potentially irreversible GlcNAc-T II inhibitors containing a photolabile 3-O-(4,4-azo)pentyl group and a 3-O-(5-iodoacetamido)pentyl group respectively. The data indicate that none of the hydroxyls of the Man1-6 residue are essential for binding although the 2- and 3-OH face the catalytic site of the enzyme. The 4-OH group of the Man-O-octyl residue is not essential for binding or catalysis since the 4-deoxy derivative is a good substrate; the 4-O-methyl derivative does not bind. This contrasts with GlcNAc-T I which cannot bind to the 4-deoxy-Man- substrate analogue. The data are compatible with our previous observations that a bisectingN-acetylglucosamine at the 4-OH position prevents both GlcNAc-T I and GlcNAc-T II catalysis. However, in the case of GlcNAc-T II, the bisectingN-acetylglucosamine prevents binding due to steric hindrance rather than to removal of an essential OH group. The 3-OH of the Man1-3 is an essential group for GlcNAc-T II since the 3-deoxy derivative does not bind to the enzyme. The trisaccharide GlcNAc1-2Man1-3Man-O-octyl is a good inhibitor (K
i=0.9mm). The above data together with previous studies indicate that binding of the GlcNAc1-2Man1-3Man- arm of the branched substrate to the enzyme is essential for catalysis.
Abbreviations: GlcNAc-T I, UDP-GlcNAc:Man1-3R (1-2)-N-acetylglucosaminyltransferase I (EC 2.4.1.101); GlcNAc-T II, UDP-GlcNAc:Man1-6R (1-2)-N-acetylglucosaminyltransferase II (EC 2.4.1.143); MES, 2-(N-morpholino)ethane sulfonic acid monohydrate. 相似文献