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21.
Summary Characteristics of inorganic carbon assimilation by photosynthesis in seawater were investigated in six species of the Fucales (five Fucaceae, one Cystoseiraceae) and four species of the Laminariales (three Laminariaceae, one Alariaceae) from Arbroath, Scotland. All of the algae tested could photosynthesise faster at high external pH values than the uncatalysed conversion of HCO
3
-
to CO2 can occur, i.e. can use external HCO
3
-
. They all had detectable extracellular carbonic anhydrase activity, suggesting that HCO
3
-
use could involve catalysis of external CO2 production, a view supported to some extent by experiments with an inhibitor of carbonic anhydrase. All of the algae tested had CO2 compensation concentrations at pH 8 which were lower than would be expected from diffusive entry of CO2 supplying RUBISCO as the initial carboxylase, consistent with the operation of energized entry of HCO
3
-
and / or CO2 acting as a CO2 concentrating mechanism. Quantitative differences among the algae examined were noted with respect to characteristics of inorganic C assimilation. The most obvious distinction was between the eulittoral Fucaceae, which are emersed for part of, or most of, the tidal cycle, and the other three families (Cystoseiraceae, Laminariaceae, Alariaceae) whose representatives are essentially continually submersed. The Fucaceae examined are able to photosynthesise at high pH values, and have lower CO2 compensation concentrations, and lower K1/2 values for inorganic C use in photosynthesis, at pH 8, than the other algae tested. Furthermore, the Fucaceae are essentially saturated with inorganic C for photosynthesis at the normal seawater concentration at pH 8 and 10°C. These characteristics are consistent with the dominant role of a CO2 concentrating mechanism in CO2 acquisition by these plants. Other species tested have characteristcs which suggest a less effective HCO
3
-
use and CO2 concentrating mechanism, with the Laminariaceae being the least effective; unlike the Fucaceae, photosynthesis by these algae is not saturated with inorganic C in normal seawater. Taxonomic and ecological implications of these results are considered in relation to related data in the literature. 相似文献
22.
Archaeoglobus fulgidus is an extremely thermophilic archaebacterium that can grow at the expense of lactate oxidation with sulfate to CO2 and H2S. The organism contains coenzyme F420, tetrahydromethanopterin, and methanofuran which are coenzymes previously thought to be unique for methanogenic bacteria. We report here that the bacterium contains methylenetetrahydromethanopterin: F420 oxidoreductase (20 U/mg), methenyltetrahydromethanopterin cyclohydrolase (0.9 U/mg), formyltetrahydromethanopterin: methanofuran formyltransferase (4.4 U/mg), and formylmethanofuran: benzyl viologen oxidoreductase (35 mU/mg). Besides these enzymes carbon monoxide: methyl viologen oxidoreductase (5 U/mg), pyruvate: methyl viologen oxidoreductase (0.7 U/mg), and membranebound lactate: dimethylnaphthoquinone oxidoreductase (0.1 U/mg) were found. 2-Oxoglutarate dehydrogenase, which is a key enzyme of the citric acid cycle, was not detectable. From the enzyme outfit it is concluded that in A. fulgidus lactate is oxidized to CO2 via a modified acetyl-CoA/carbon monoxide dehydrogenase pathway involving C1-intermediates otherwise only used by methanogenic bacteria.Non-standard abbreviations APS
adenosine 5-phosphosulfate
- BV
benzyl viologen
- DCPIP
2,6-dichlorophenolindophenol
- DMN
2,3-dimethyl-1,4-naphthoquinone
- DTT
DL-1,4-dithiothreitol
- H4F
tetrahydrofolate
- H4MPT
tetrahydromethanopterin
- CH2
H4MPT, methylene-H4MPT
- CH
H4MPT, methenyl-H4MPT
- Mes
morpholinoethane sulfonic acid
- MFR
methanofuran
- Mops
morpholinopropane sulfonic acid
- MV
methyl viologen
- Tricine
N-tris(hydroxymethyl)-methylglycine
- U
mol product formed per min 相似文献
23.
Hepatic coma was induced in rats chronically treated with CCl4, by means of a single injection of ammonium acetate. The activities of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T), as well as the synaptosomal uptake and release of [3H]GABA, were measured in the following brain areas of the comatose rats: cortex, striatum, hypothalamus, hippocampus, midbrain and cerebellum. Hepatic coma was associated with a general decrease of GAD activity, whereas GABA-T activity was diminished only in the hypothalamus, striatum and midbrain. During hepatic coma, the K+-stimulated [3H]GABA release was notably diminished in the striatum and cerebellum, whereas a significant increase was observed in the hippocampus. [3H]GABA uptake increased in most regions after CCl4 treatment, independently of the presence of coma. The results indicate that GABAergic transmission seems to be decreased in most cerebral regions during hepatic coma. 相似文献
24.
Analysing partitioning of recently fixed and of reserve carbon in reproductive Phaseolus vulgaris L. plants 总被引:3,自引:2,他引:1
Abstract. Partitioning of recently-fixed carbon among plant organs and subsequent distribution of reserve carbon were studied by supplying whole shoots of bean plants ( Phaseolus vulgaris L.) with 14 C-labelled CO2 of constant specific radioactivity throughout a photoperiod. The gain of tracer carbon in each part revealed net accumulation of recently-fixed carbon from direct fixation, import or both. Growth rate coefficients describing the present pattern of plant growth were calculated from ratios of tracer carbon to total carbon present in plant organs and were used to project future plant form. The period 10–20 d after the start of flowering was marked by a major increase in partitioning of recently-fixed carbon to reproductive growth. Growth rates for the plant and its parts during this period were projected on the basis of growth rate coefficients and were found to be similar to rates measured by gravimetric growth analysis. Changes in tracer carbon recovered in individual organs after chase periods of various lengths revealed net decreases for leaves and stems. About 9% of the carbon distributed to fruits came from reserves even in the absence of obvious stress. Respiratory loss during the chase period was determined from the progressive drop in recovery of the original tracer carbon. The methods are being applied to measure current net accumulation rates in studies of sink organ physiology, and to compare partitioning of recently-fixed and of stored carbon in several plant species under defined growth conditions. 相似文献
25.
J. A. BUNCE 《Plant, cell & environment》1988,11(3):205-208
Abstract. Gas exchange measurements were made on single leaves of three C3 and one C4 species at air speeds of 0.4 and 4.0 m s−1 to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m−2 s−1 at the lower air speed, and 1.2 to 1.5 mol m−2 s−1 at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C3 species, and about 3 Pa lower in the C4 species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C3 species. The commonly reported values of substomatal carbon dioxide pressure for C3 and C4 species were found to occur only when measurements were made at the higher air speed. 相似文献
26.
In vitro enzyme activities of glycolysis, pentose-phosphate pathway and dark CO2 fixation were assayed in batch cultures of heterotrophic Catharanthus roseus cells under various gassing rates and partial pressures of carbon dioxide. Detrimental effects of low pCO2 culture conditions on the growth characteristics could be linked to marked changes in levels of enzymes of primary metabolism during growth. The enzyme levels observed during the early stages of growth were found to be more stable when a constant pCO2 (20 mbar) was maintained and enabled exponential growth to be reached more rapidly.The importance of carbon dioxide as a conditioning factor of the culture medium is discussed. 相似文献
27.
Richard C. Leegood Carlos A. Labate Steven C. Huber H. Ekkehard Neuhaus Mark Stitt 《Planta》1988,176(1):117-126
Glycerol induced a limitation on photosynthetic carbon assimilation by phosphate when supplied to leaves of barley (Hordeum vulgare L.) and spinach (Spinacia oleracea L.). This limitation by phosphate was evidenced by (i) reversibility of the inhibition of photosynthesis by glycerol by feeding orthophosphate (ii) a decrease in light-saturated rates of photosynthesis and saturation at a lower irradiance, (iii) the promotion of oscillations in photosynthetic CO2 assimilation and in chlorophyll fluorescence, (iv) decreases in the pools of hexose monophosphates and triose phosphates and increases in the ratio of glycerate-3-phosphate to triose phosphate, (v) decreased photochemical quenching of chlorophyll fluorescence, and increased non-photochemical quenching, specifically of the component which relaxed rapidly, indicating that thylakoid energisation had increased. In barley there was a massive accumulation of glycerol-3-phosphate and an increase in the period of the oscillations, but in spinach the accumulation of glycerol-3-phosphate was comparatively slight. The mechanism(s) by which glycerol feeding affects photosynthetic carbon assimilation are discussed in the light of these results.Abbreviations Chl
chlorophyll
- C
i
intercellular concentration of CO2
- P
phosphate
- PGA
glycerate-3-phosphate
- Pi
orthophosphate
- triose-P
sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate 相似文献
28.
Collagen gene expression during volume overload-induced cardiac hypertrophy was investigated in adult male rats. Hypertrophy of the left ventricle (22%) and right ventricle (37%) occurred following 27 days continuous exposure to 700 ppm carbon monoxide; hematocrit increased nearly 47%. To examine potential cellular and molecular control of restructuring in the heart, we investigated the expression of two specific procollagen mRNAs for collagen types which have different structural-functional roles [Type I (alpha-1) & Type IV]. Type I (interstitial) mRNA levels increased at least 100% relative to controls within 3 days of initial exposure to 700ppm CO, then declined afterwards; type IV(basement membrane) mRNA levels increased more modestly at first, and increased further afterwards. The ratio of type I/type IV RNA's also increased initially, then later declined, with the greatest differences in the relative responses of type I and IV mRNAs seen in the right ventricle. These data suggest that types I and IV collagen mRNA expression is not coordinately expressed during this type of volume overload-induced hypertrophy in rat heart. 相似文献
29.
A continuous-culture approach to the question of inorganic carbon concentration by Synechococcus species 总被引:1,自引:0,他引:1
Abstract Chemostat cultures of Synechococcus PCC7942 were established in steady state over ten generations with inorganic carbon-limiting biomass production. The bicarbonate-concentration process was not significantly induced; RuBisCo activity was increased six-fold with decreasing dissolved inorganic carbon concentration and the presence of the 42-kDa cytoplasmic membrane polypeptide was observed but not implicated in the process. 相似文献
30.
Abstract. Gas exchange measurements were performed to test the hypothesis that failure of stomata to open in senescing leaves of Nicotiana glauca is caused by elevated concentrations of carbon dioxide in the intercellular spaces of leaf mesophyll tissue (ci ). Senescing leaves selected for experiments were completely chlorotic and lacked positive rates of photosynthesis. When stomata in detached epidermis from senescing leaves were illuminated in CO2-free air, they opened to similar apertures as those in detached epidermis from nonsenescing leaves. To compare the effects of changes in ci on stomatal responses of the two leaf types, leaf 'flags' of either nonsenescing or senescing leaves were illuminated at a photosynthetic photon flux density of 500 μmol m−2 s−1 in a gas exchange cuvette. Leaf temperatures were maintained at 23.5 ± 0.5°C, and vapour pressure differences between leaves and the air were maintained between 0.70 and 0.75kPa. Ci was adjusted by changing external concentrations of carbon dioxide in air circulating through the cuvette. Conductances and photosynthetic rates of nonsenescing leaves changed in response to changes in ci , but neither the conductances nor the photosynthetic rates of senescing leaves were affected significantly by changes in q. We conclude that guard cells of senescing leaves of Nicotiana glauca do not lose the capacity to respond to changes in carbon dioxide concentration and that increases in ci resulting from declining rates of mesophyll photosynthesis are not the sole cause of maintenance of stomatal closure during leaf senescence. The data suggest that factors external to guard cells may prevent them from responding to changes in carbon dioxide concentrations in intact senescing leaves. 相似文献