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1.
In C4 grasses belonging to the NADP-malic enzyme-type subgroup, malate is considered to be the predominant C4 acid metabolized during C4 photosynthesis, and the bundle sheath cell chloroplasts contain very little photosystem-II (PSII) activity. The present studies showed that Flaveria bidentis (L.), an NADP-malic enzyme-type C4 dicotyledon, had substantial PSII activity in bundle sheath cells and that malate and aspartate apparently contributed about equally to the transfer of CO2 to bundle sheath cells. Preparations of bundle sheath cells and chloroplasts isolated from these cells evolved O2 at rates between 1.5 and 2 mol · min–1 · mg–1 chlorophyll (Chl) in the light in response to adding either 3-phosphoglycerate plus HCO
3
–
or aspartate plus 2-oxoglutarate. Rates of more than 2 mol O2 · min–1 · mg–1 Chl were recorded for cells provided with both sets of these substrates. With bundle sheath cell preparations the maximum rates of light-dependent CO2 fixation and malate decarboxylation to pyruvate recorded were about 1.7 mol · min–1 · mg–1 Chl. Compared with NADP-malic enzyme-type grass species, F. bidentis bundle sheath cells contained much higher activities of NADP-malate dehydrogenase and of aspartate and alanine aminotransferases. Time-course and pulse-chase studies following the kinetics of radiolabelling of the C-4 carboxyl of C4 acids from 14CO2 indicated that the photosynthetically active pool of malate was about twice the size of the aspartate pool. However, there was strong evidence for a rapid flux of carbon through both these pools. Possible routes of aspartate metabolism and the relationship between this metabolism and PSII activity in bundle sheath cells are considered.Abbreviations DHAP
dihydroxyacetone phosphate
- NADP-ME(-type)
NADP-malic enzyme (type)
- NADP-MDH
NADP-malate dehydrogenase
- OAA
oxaloacetic acid
- 2-OG
2-oxoglutarate
- PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- Pi
orthophosphate
- Ru5P
ribulose 5-phosphate 相似文献
2.
Summary When discs punched out of the median part of the phylloid of Laminaria saccharina Lamour. were exposed to H14CO3
- in the light for periods of 10 sec to 10 min, 14C was rapidly incorporated into various photosynthetic products. As compared with dark fixation, 14C-photosynthesis increased exponentially during the first 60 sec of incubation in H14CO3
-. Fixation rates were found to be 76 mol CO2·dm-2·h-1 or 100 mol CO2·mg-1 chlorophyll a·h-1. Eighty-five per cent of the total 14C assimilated after 10 sec was fixed in phosphoglycerate and in the sugar monophosphates, 2% in the sugar diphosphates, and only 3.5% in malate and aspartate. While the radioactivity of malate and aspartate only rose to a constant level, the percentage of the total 14C in phosphoglycerate and-to a lower extent-that in the sugar monophosphates rapidly decreased with the duration of light exposure. Simultaneously, mannitol and glycine+serine became labelled with 43% and 32% respectively of the total 14C after 10 min light fixation. In the dark, the percentage of the total 14C in malate decreased with the time of H14CO2--incubation, while there was a remarkable increase in radioactivity of aspartate and glutamate. Within 60 min darkness no labelling of mannitol was found.From the present results it is concluded that the photosynthetic carbon cycle first described by Bassham and Calvin operates in Laminaria saccharina.
Auszug aus einer Diplomarbeit. 相似文献
Auszug aus einer Diplomarbeit. 相似文献
3.
Desulfovibrio vulgaris (Marburg) was grown on hydrogen plus sulfate as sole energy source and acetate plus CO2 as the sole carbon sources. The incorporation of U-14C acetate into alanine, aspartate, glutamate, and ribose was studied. The labelling data show that alanine is synthesized from one acetate (C-2 + C-3) and one CO2 (C-1), aspartate from one acetate (C-2 + C-3) and two CO2 (C-1 + C-4), glutamate from two acetate (C-1–C-4) and one CO2 (C-5), and ribose from 1.8 acetate and 1.4 CO2. These findings indicate that in Desulfovibrio vulgaris (Marburg) pyruvate is formed via reductive carboxylation of acetyl-CoA, oxaloacetate via carboxylation of pyruvate or phosphoenol pyruvate, and -ketoglutarate from oxaloacetate plus acetyl-CoA via citrate and isocitrate. Since C-5 of glutamate is derived from CO2, citrate must have been formed via a (R)-citrate synthase rather than a(S)-citrate synthase. The synthesis of ribose from 1.8 mol of acetate and 1.4 mol of CO2 excludes the operation of the Calvin cycle in this chemolithotrophically growing bacterium. 相似文献
4.
Summary Cell suspension cultures ofChenopodium rubrum have been grown for more than 2 years photoautotrophically with CO2 as sole carbon source. Average increase in fresh weight is appr. 600% within 14 days. The chlorophyll content of photoautotrophic cells (200 g/g fresh weight) is much higher than of photomixotrophic cells (50 g/g fresh weight). The photosynthetic activity of the cells (190 moles CO2×mg–1 chlorophyllXh–1) is comparable to the values found with intact leaves. As shown by short-term14CO2 photosynthesis, both, the photomixotrophic and the photoautotrophic cell suspension cultures assimilate CO2 predominantly via the Calvin pathway.Major differences were found with cells from either exponential or stationary phase of growth with regard to differential labelling of 3-phosphoglyceric acid, malate, sucrose and glucose/fructose.In vitro measurements of carboxylation reactions only partially corroborate our findings with14CO2 incorporation. The ratio of ribulosebisphosphate to phosphoenolpyruvate carboxylase activity is 4.7 for leaves of C.rubrum, 1.2 for photoautotrophic cells during stationary growth and 0.5 for cells during exponential growth phase, however, 0.18 was found for photomixotrophic cells. Though the14CO2 incorporation into 3-phosphoglyceric acid is clearly higher than into malate, thein vitro activity of phosphoenolpyruvatecarboxylase is 2–6 fold higher than that of ribulosebisphosphate carboxylase. We postulate that anaplerotic reactions of the tricarboxylic acid cycle are involved in the regulation of phosphoenolpyruvate carboxylase.Abbreviations 2,4-D
didilorophenoxyacetic acid
- EDTA
ethylene-diamine-tetraacetic acid
- fr. w.
fresh weight
- HEPES
N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid
- PGA
3-phosphoglyceric acid
- PPO
2,5-diphenyloxazole
- PEP
phosphoenolpyruvate
- RuBP
nbulosebisphosphate 相似文献
5.
Alexander Ziegler-Jöns 《Planta》1989,178(2):164-175
Data for the maximum carboxylation velocity of ribulose-1,5-biosphosphate carboxylase, Vm, and the maximum rate of whole-chain electron transport, Jm, were calculated according to a photosynthesis model from the CO2 response and the light response of CO2 uptake measured on ears of wheat (Triticum aestivum L. cv. Arkas), oat (Avena sativa L. cv. Lorenz), and barley (Hordeum vulgare L. cv. Aramir). The ratio Jm/Vm is lower in glumes of oat and awns of barley than it is in the bracts of wheat and in the lemmas and paleae of oat and barley. Light-microscopy studies revealed, in glumes and lemmas of wheat and in the lemmas of oat and barley, a second type of photosynthesizing cell which, in analogy to the Kranz anatomy of C4 plants, can be designated as a bundle-sheath cell. In wheat ears, the CO2-compensation point (in the absence of dissimilative respiration) is between those that are typical for C3 and C4 plants.A model of the CO2 uptake in C3–C4 intermediate plants proposed by Peisker (1986, Plant Cell Environ. 9, 627–635) is applied to recalculate the initial slopes of the A(pc) curves (net photosynthesis rate versus intercellular partial pressure of CO2) under the assumptions that the Jm/Vm ratio for all organs investigated equals the value found in glumes of oat and awns of barley, and that ribulose-1,5-bisphosphate carboxylase is redistributed from mesophyll to bundle-sheath cells. The results closely match the measured values. As a consequence, all bracts of wheat ears and the inner bracts of oat and barley ears are likely to represent a C3–C4 intermediate type, while glumes of oat and awns of barley represent the C3 type.Abbreviations A
net photosynthesis rate (mol·m-2·s-1)
- Jm
maximum rate of whole-chain electron transport (mol·e-·m-2·s-1)
- pc (bar)
intercellular partial pressure of CO2
- PEP
phosphoenolpyruvate
- PPFD
photosynthetic photon flux density (mol quanta·m-2·s-1)
- RuBPCase
ribulose bisphosphate carboxylase/oxygenase
- RuBP
ribulose bisphosphate
- Vm
maximum carboxylation velocity of RuBPCase (mol·m-2·s-1)
- T*
CO2 compensation point in the absence of dissimilative respiration (bar) 相似文献
6.
Comparative 14CO2 pulse-12CO2 chase studies performed at CO2 compensation ()-versus air-concentrations of CO2 demonstrated a four-to eightfold increase in assimilation of 14CO2 into the C4 acids malate and aspartate by leaves of the C3-C4 intermediate species Panicum milioides Nees ex Trin., P. decipiens Nees ex Trin., Moricandia arvensis (L.) DC., and M. spinosa Pomel at . Specifically, the distribution of 14C in malate and aspartate following a 10-s pulse with 14CO2 increases from 2% to 17% (P. milioides) and 4% to 16% (M. arvensis) when leaves are illuminated at the CO2 compensation concentration (20 l CO2/l, 21% O2) versus air (340 l CO2/l, 21% O2). Chasing recently incorporated 14C for up to 5 min with 12CO2 failed to show any substantial turnover of label in the C4 acids or in carbon-4 of malate. The C4-acid labeling patterns of leaves of the closely related C3 species, P. laxum Sw. and M. moricandioides (Boiss.) Heywood, were found to be relatively unresponsive to changes in pCO2 from air to . These data demonstrate that the C3-C4 intermediate species of Panicum and Moricandia possess an inherently greater capacity for CO2 assimilation via phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) at the CO2 compensation concentration than closely related C3 species. However, even at , CO2 fixation by PEP carboxylase is minor compared to that via ribulosebisphosphate carboxylase (EC 4.1.1.39) and the C3 cycle, and it is, therefore, unlikely to contribute in a major way to the mechanism(s) facilitating reduced photorespiration in the C3-C4 intermediate species of Panicum and Moricandia.Abbreviations Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- PEP
phosphoenolpyruvate
-
CO2 compensation concentration
- 3PGA
3-phosphoglycerate
- SuP
sugar monophosphates
- SuP2
sugar bisphosphates
Published as Paper No. 8249, Journal Series, Nebraska Agricultural Research Division 相似文献
7.
Further studies on a new pathway of photosynthetic carbon dioxide fixation in sugar-cane and its occurrence in other plant species 总被引:28,自引:6,他引:22
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1. The pathway of photosynthesis in sugar-cane, which gives most of the radio-activity fixed during short periods in 14CO2 in C-4 of oxaloacetate, malate and aspartate, was examined under varied conditions. 2. The pattern of labelling was essentially the same with leaves of different ages and with leaves equilibrated at carbon dioxide concentrations in the range 0–3·8% (v/v) and light-intensities in the range 1400–9000ft.-candles before adding 14CO2. 3. Radioactive products were examined after exposing leaves of 33 different plant species to 14CO2 for 4sec. under standard conditions. 4. A labelling pattern typical of sugar-cane was found in several species of Gramineae but not in others. Of 16 species from other Families only a species of Cyperaceae contained a large proportion of the fixed radioactivity in oxaloacetate, malate and aspartate. 相似文献
8.
The effect of phosphate feeding on the influence of low (2%) oxygen on photosynthetic carbon assimilation has been investigated in leaf discs of spinach (Spinacia oleracea L.) at 12°C. The following observations were made. First, after the transition from 20% O2 to 2% O2, the rate of CO2 uptake was inhibited at CO2 concentrations between about 250 and about 800 l CO2·l-1. Second, phosphate feeding stimulated the rate of CO2 uptake in 20% O2 at higher concentrations of CO2 (500–900 l·l-1). Third, phosphate feeding stimulated the rate of CO2 uptake in 2% O2 at all but the highest (900 l·l-1) and lowest 74 (l·l-1) concentrations of CO2 employed. Phosphate thereby restored the stimulation of photosynthesis by 2% O2 and it did so over a wide range of lower temperatures. Fourth, oscillatory behaviour, however generated, was dampened by phosphate feeding, even at very low concentrations of CO2. Contents of leaf metabolites were measured during the transition to 2% O2 in control and phosphate-fed leaf discs. During this period the ratio glycerate-3-phosphate/triose phosphate rose steeply, but fell again only in the phosphate-treated leaf discs. These data, taken together with measured ATP/ADP ratios, showed that assimilatory power, the ratio [ATP]·[NAD(P)H]/[ADP]·[Pi]·[NAD(P)], decreased when leaves were exposed to 2% O2, but that this decrease was minimised by previous feeding of phosphate. The mechanism of phosphate limitation is discussed in the light of the results.Abbreviations Ci
intercellular concentration of CO2
- RuBP
ribulose-1,5-bisphosphate 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.
Summary The effects of CO2 enrichment and water stress on gas exchange of Liquidambar styraciflua L. (sweetgum) and Pinus taeda L. (loblolly pine) seedlings were examined for individuals grown from seed under high (1000 mol·m-2·s-1) and low (250 mol·m-2·s-1) photosynthetic photon flux density at 350, 675 and 1000 l·l-1 CO2. At 8 weeks of age, half the seedlings in each CO2-irradiance treatment were subjected to a drying cycle which reduced plant water potential to about -2.5 MPa in the most stressed plants, while control plants remained well-watered (water potentials of -0.3 and -0.7 MPa for sweetgum and loblolly pine, respectively). During this stress cycle, whole seedling net photosynthesis, transpiration and stomatal conductance of plants from each CO2-irradiance-water treatment were measured under respective growth conditions.For both species, water stress effects on gas exchange were greatest under high irradiance conditions. Waterstressed plants had significantly lower photosynthesis rates than well-watered controls throughout most of the drying cycle, with the most severe inhibition occurring for low CO2, high irradiance-grown sweetgum seedlings. Carbon dioxide enrichment had little effect on gas exchange rates of either water-stressed or well-watered loblolly pine seedlings. In contrast, water stress effects were delayed for sweetgum seedlings grown at elevated CO2, particularly in the 1000 l·l-1 CO2, high irradiance treatment where net photosynthesis, transpiration and conductance of stressed plants were 60, 36 and 33% of respective control values at the end of the drying cycle. Development of internal plant water deficits was slower for stressed sweetgum seedlings grown at elevated CO2. As a result, these seedlings maintained higher photosynthetic rates over the drying cycle than stressed sweetgum seedlings grown at 350 l·l-1 CO2 and stressed loblolly pine seedlings grown at ambient and enriched CO2 levels. In addition, water-stressed sweetgum seedlings grown at elevated CO2 exhibited a substantial increase in water use efficiency.The results suggest that with the future increase in atmospheric CO2 concentration, sweetgum seedlings should tolerate longer exposure to low soil moisture, resulting in greater first year survival of seedlings on drier sites of abandoned fields in the North Carolina piedmont. 相似文献
11.
Measurement of the light response of photosynthetic CO2 uptake is often used as an implement in ecophysiological studies. A method is described to calculate photosynthetic parameters, such as the maximum rate of whole electron transport and dissimilative respiration in the light, from the light response of CO2 uptake. Examples of the light-response curves of flag leaves and ears of wheat (Triticum aestivum cv. ARKAS) are shown.Abbreviations and symbols A
net photosynthesis rate
-
D
1
rate of dissimilative respiration occurring in the light
-
f
loss factor
-
I
incident PPFD
-
I
effective absorbed PPFD
-
J
rate of whole electron transport
-
J
m
maximum rate of whole electron transport
-
p
c
intercellular CO2 partial pressure
- PPFD
photosynthetic photon flux density
-
q
effectivity factor for the use of light (electrons/quanta)
-
absorption coefficient
-
I
*
CO2 compensation point in the absence of dissimilative respiration (bar)
-
II
conversion factor for calculation of CO2 uptake from the rate of whole electron transport
-
convexity factor
Gas-exchange rates relate to the projective area and are given in mol·m-2·s-1. Electron-transport rates are given in mol electrons·m-2·s-1; PPFD is given in mol quanta·m-2·s-1. 相似文献
12.
W. Schmidt Th. Scheper Prof. Dr. K. Schügerl 《Bioprocess and biosystems engineering》1988,3(3):129-133
Ethanol was produced with Zymomonas mobilis Z6 (ATCC 29191), in batch culture with synthetic medium on glucose as substrate and in the presence of aspartate. The concentrations of glucose, phosphate, ammonium, ethanol and dissolved O2 and CO2 in the medium and O2 and CO2 in the outlet gas as well as the cell mass by culture fluorescence were measured on-line. Cell mass, glucose and aspartate concentrations were measured off-line. In the presence of a sufficient amount of aspartate, the ethanol inhibition effect can be reduced considerably. However, the improvement with yeast extract is more incisive. The relationship between the intensity of culture fluorescence and cell mass concentration is linear, if sufficient aspartate is present.List of Symbols ASP kg/m3
aspartate concentration
-
CTR kg/(m3 · h)
CO2 transfer rate
- N, NH4 kg/m3
nitrogen concentration from NH
4
+
-
P kg/m3
product (ethanol) concentration
-
p%
product (ethanol) yield
- PO4 kg/m3
phosphate concentration
-
Q
E
kg/(kg · h)
specific ethanol production rate
-
kg/(kg · h)
specific nitrogen uptake rate from NH
4
+
-
Q
P
kg/(kg · h)
specific phosphate uptake rate
-
Q
s
kg/(kg · h)
specific substrate (glucose) uptake rate
-
S kg/m3
glucose concentration
-
S
O
kg/m3
initial glucose concentration
-
Y
x/s
kg/kg
yield coefficient
-
h–1
specific growth rate 相似文献
13.
The activities of several enzymes, including ribulose-1,5-diphosphate (RuDP) carboxylase (EC 4.1.1.39) and phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured as a function of leaf age in Z. mays. Mature leaf tissue had a RuDP-carboxylase activity of 296.7 mol CO2 g-1 fresh weight h-1 and a PEP-carboxylase activity of 660.6 mol CO2 g-1 fresh weight h-1. In young corn leaves the activity of the two enzymes was 11 and 29%, respectively, of the mature leaves. In senescent leaf tissue, RuDP carboxylase activity declined more rapidly than that of any of the other enzymes assayed. On a relative basis the activities of NADP malic enzyme (EC 1.1.1.40), aspartate (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2), and NAD malate dehydrogenase (EC 1.1.1.37) exceeded those of both PEP and RuDP carboxylase in young and senescent leaf tissue. Pulse-chase labeling experiments with mature and senescent leaf tissue show that the predominant C4 acid differs between the two leaf ages. Labeling of alanine in senescent tissue never exceeded 4% of the total 14C remaining during the chase period, while in mature leaf tissue alanine accounted for 20% of the total after 60 s in 12CO2. The activity of RuDP carboxylase during leaf ontogeny in Z. mays parallels the development of the activity of this enzyme in C3 plants.Abbreviations RuDP
ribulose-1,5-diphosphate
- PEP
phosphoenol pyruvate
- PGA
3-phosphoglycerate 相似文献
14.
The involvement of reactions of the tricarboxylic acid cycle in autotrophic CO2 fixation in Methanobacterium thermoautotrophicum was investigated. The incorporation of succinate into glutamate (=-ketoglutarate), aspartate (=oxaloacetate) and alanine (=pyruvate) was studied. The organism was grown on H2 plus CO2 at pH 6.5 in the presence of 1 mM [U-14C-]succinate. Significant amounts of the dicarboxylic acid were incorporated into cellular material under these conditions. Alanine, aspartate, and glutamate were isolated and their specific radioactivities were determined. Only glutamate was found to be labelled. Degradation of glutamate revealed that C-1 of glutamate was derived from CO2 and C-2-C-5 from succinate indicating that in M. thermoautotrophicum -ketoglutarate is synthesized via reductive carboxylation of succinyl CoA. The finding that succinate was not incorporated into alanine and aspartate excludes that oxaloacetate and pyruvate are synthesized from -ketoglutarate via isocitrate or citrate. This is taken as evidence that a complete reductive carboxylic acid cycle is not involved here in autotrophic CO2 fixation. 相似文献
15.
16.
Summary Kinetic studies on the release of [14C] malate into unlabelled buffer in tissue slices of Bryophyllum leaves labelled by 14CO2 dark fixation showed a curve characterized by three phases. According to literature, these phases indicate malate efflux from free space, cytoplasm and vacuoles. From the curves obtained it could be estimated that the cytoplasmatic pool of [14C] malate after 14CO2 dark fixation is higher in acidified tissue (i.e. high malate content) than in deacidified tissue (i.e. low malate content). Efflux of [14C] malate from the vacuoles is also higher in acidified tissue. It increases when the malate solution enclosed in the vacuoles becomes more concentrated. This could be demonstrated in experiments in which water was extracted from the labelled tissue by raising the osmotic potential of the buffers in which the tissue slices were suspended. The increase of [14C] malate efflux from the vacuoles followed a sigmoid curve when plotted against the osmotic potential of the washing buffer, i.e. agaisnt the degree of dehydratation of the tissue.The osmotic potential of the buffer in which leaf tissue of Bryophyllum was suspended also had an effect on the distribution of radiocarbon among the metabolites when the tissue was allowed to fix 14CO2 in the light. In deacidified tissue the incorporation of 14C into malate was inhibited whereas label found in carbohydrates (starch + sucrose) remained nearly unchanged when the osmotic potential of the buffer increased up to 12 atm. This effect is explained in terms of inhibition of PEP-carboxylase by a growing cytoplasmic malate pool, which is caused by the increasing malate efflux from the vacuole and by retarded malate flux from cytoplasm into vacuole under these conditions. However, in acidified tissue labelling of malate was already low with no osmotic stress, and no further inhibition of malate synthesis could be observed when the osmotic potential of the buffer was increased.Label found in starch after 14CO2–fixation decreased in the light under osmotic stress, with more label being transferred into sucrose. This effect could be interpreted as osmoregulation which forces the cells of the leaf tissue to produce osmotically effective substances to balance the higher osmotic potential of the buffer.
Abkürzungen und Symbole CAM Crassulacean Acid Metabolism - FW Frischgewicht - PEP Phosphoenolpyruvat - * potentieller osmotischer Druck 相似文献
Abkürzungen und Symbole CAM Crassulacean Acid Metabolism - FW Frischgewicht - PEP Phosphoenolpyruvat - * potentieller osmotischer Druck 相似文献
17.
D. Overdieck 《International journal of biometeorology》1985,29(1):57-65
The CO2 gas exchange rates of the Central European perennial understory plantAsarum europaeum L. were measured in late autumn (October 30 to November 30) in its natural habitat day and night.During these measurements the temperature ranged from 0 to 15°C and the absolute air humidity from 3 to 10 mg H2O·1–1. Temperature and absolute air humidity over these ranges did not affect CO2 net assimilation which was determined almost entirely by quantum flux density.CO2 net assimilation was light saturated at about 100 M·m–2·s–1 quantum flux density. The uptake rate at this point was 4.3 mg·dm–2·h–1. The compensation point occurred at approximately 1 M·m–2·s–1. 相似文献
18.
Summary Photosynthetic characteristics of two important grasses of Indian desert have been studied. Pennisetum typhoides, an important cereal crop, known to have Kranz-type leaf anatomy and low CO2-compensation point, shows the C-4-dicarboxylic acid pathway for photosynthetic carbon reduction. Lasiurus sindicus, a promising forage grass, has also been shown to possess, for the first time, a typical Kranz-type leaf anatomy and a very similar CO2-fixation pattern like Pennisetum typhoides. It is remarkable that both species after short time exposure to 14CO2 show a high labelling not only in malate but also in alanine. This may be due to the activity of an aspartic acid decarboxylase. 相似文献
19.
Phosphoenolpyruvate carboxylase activity in extracts of a wide range of thermogenic tissues of the Araceae was shown to be in the range 10–100 mol g-1 fresh weight min-1 (0.5–3.7 mol mg-1 protein min-1). Such high activities were not found in non-thermogenic tissues of the Araceae or in thermogenic tissues of Aristolochia brasiliensis Mart. and Zucc., Victoria amazonica Schomb. and Encephalartos barteri Carruth. During development and thermogenesis in the club of Arum maculatum L. the high activities of the carboxylase did not lead to any marked accumulation of citrate, isocitrate, 2-oxoglutarate, fumarate, malate and oxaloacetate. Clubs of Arum maculatum and of Arum italicum Miller readily fixed 14CO2 in the dark, mostly into aspartate, malate, alanine and glutamate. Pulse and chase experiments showed that most of the fixed carbon was very rapidly metabolized to CO2. The detailed distribution suggest that this occurred largely by decarboxylation of C-4 acids. It is suggested that thermogenic tissues of the Araceae are characterized by very high activities of phosphoenolpyruvate carboxylase, and that in vivo this leads to synthesis of C-4 acids which are promptly decarboxylated. 相似文献
20.
Carlos Vílchez Francisco Galván José M. Vega 《Applied microbiology and biotechnology》1991,35(6):716-719
Summary
Chlamydomonas reinhardtii cells provide an effective system for glycolate photoproduction, operative during 30 h when they are growing under low CO2, in the presence of 1 mM aminooxyacetate and 50 M acetazolamide. Glycolate excretion by the cells can proceed for about 4 days if every other 12 h a high CO2 level is restored in the culture in the absence of inhibitors. The immobilized system in alginate beads has about a twofold higher glycolate photoproduction rate (23 mol·mg chlorophyll (Chl)–1·h–1) than free-living cells (12 mol · mg Chl–1 · h–1).
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