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1.
Benzylaminopurine (BA) caused an enhancement of chlorophyll and protein content and a reduced elongation of primary barley leaves. BA did not change the rhythmic pattern of14CO2 fixation and activities of RuBP carboxylase, RuBP oxygenase, glycolate oxidase and phosphoglycolate phosphatase, but the enzyme activities were enhanced and the level of14CO2 fixation was reduced. Light/dark14CO2 evolution ratio was affeoted by BA only in older leaves. BA acts sequentially on the activities of photosynthetic and photorespiratory enzymes. 相似文献
2.
The applicability of two methods (pyrolysis gas chromatography and acidification-wet oxidation) for determining14CO2 incorporation into soil microorganisms was investigated. Both methods were able to distinguish biologically incorporated14C from abiotically adsorbed14C, but to varying degrees, there being a larger carryover of abiotic14C into the organic fraction and a higher percentage of assimilated14C in the organic fraction with the wet oxidation method. Using14C assimilation as a measure, it was possible to determine microbial activities in soils of diverse properties under a variety
of conditions, including polar soils under harsh environmental conditions. Both light and dark14CO2 fixation was measurable.14CO2 assimilation was not always proportional to the enumerable microorganisms. A new design for measurement of microbial activityin situ enabled measurement of total C influx (primary productivity) into soils with minimal perturbation to the natural soil ecosystem. 相似文献
3.
The lichen Peltigera aphthosa consists of a fungus and green alga (Coccomyxa) in the main thallus and of a Nostoc located in superficial packets, intermixed with fungus, called cephalodia. Dark nitrogenase activity (acetylene reduction) of lichen discs (of alga, fungus and Nostoc) and of excised cephalodia was sustained at higher rates and for longer than was the dark nitrogenase activity of the isolated Nostoc growing exponentially. Dark nitrogenase activity of the symbiotic Nostoc was supported by the catabolism of polyglucose accumulated in the ligh and which in darkness served to supply ATP and reductant. The decrease in glucose content of the cephalodia paralleled the decline in dark nitrogenase activity in the presence of CO2; in the absence of CO2 dark nitrogenase activity declined faster although the rate of glucose loss was similar in the presence and absence of CO2. Dark CO2 fixation, which after 30 min in darkness represented 17 and 20% of the light rates of discs and cephalodia, respectively, also facilitated dark nitrogenase activity. The isolated Nostoc, the Coccomyxa and the excised fungus all fixed CO2 in the dark; in the lichen most dark CO2 fixation was probably due to the fungus. Kinetic studies using discs or cephalodia showed highest initial incorporation of 14CO2 in the dark in to oxaloacetate, aspartate, malate and fumarate; incorporation in to alanine and citrulline was low; incorporation in to sugar phosphates, phosphoglyceric acid and sugar alcohols was not significant. Substantial activities of the enzymes phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and carbamoyl-phosphate synthase (EC 2.7.2.5 and 2.7.2.9) were detected but the activities of PEP carboxykinase (EC 4.1.1.49) and PEP carboxyphosphotransferase (EC 4.1.1.38) were negligible. In the dark nitrogenase activity by the cephalodia, but not by the free-living Nostoc, declined more rapidly in the absence than in the presence of CO2 in the gas phase. Exogenous NH
4
+
inhibited nitrogenase activity by cephalodia in the dark especially in the absence of CO2 but had no effect in the light. The overall data suggest that in the lichen dark CO2 fixation by the fungus may provide carbon skeletons which accept NH
4
+
released by the cyanobacterium and that in the absence of CO2, NH
4
+
directly, or indirectly via a mechanism which involves glutamine synthetase, inhibits nitrogenase activity.Abbreviations CP
carbamoyl phosphate
- EDTA
ethylenedi-amine tetraacetic acid
- PEP
phosphoenolpyruvate
- RuBP
ribulose 1,5 bisphosphate 相似文献
4.
Manuela Hartmann Paola Gomez-Pereira Carolina Grob Martin Ostrowski David J Scanlan Mikhail V Zubkov 《The ISME journal》2014,8(11):2280-2289
Nearly half of the Earth''s surface is covered by the ocean populated by the most abundant photosynthetic organisms on the planet—Prochlorococcus cyanobacteria. However, in the oligotrophic open ocean, the majority of their cells in the top half of the photic layer have levels of photosynthetic pigmentation barely detectable by flow cytometry, suggesting low efficiency of CO2 fixation compared with other phytoplankton living in the same waters. To test the latter assumption, CO2 fixation rates of flow cytometrically sorted 14C-labelled phytoplankton cells were directly compared in surface waters of the open Atlantic Ocean (30°S to 30°N). CO2 fixation rates of Prochlorococcus are at least 1.5–2.0 times higher than CO2 fixation rates of the smallest plastidic protists and Synechococcus cyanobacteria when normalised to photosynthetic pigmentation assessed using cellular red autofluorescence. Therefore, our data indicate that in oligotrophic oceanic surface waters, pigment minimisation allows Prochlorococcus cells to harvest plentiful sunlight more effectively than other phytoplankton. 相似文献
5.
Crous KY Zaragoza-Castells J Ellsworth DS Duursma RA Löw M Tissue DT Atkin OK 《Plant, cell & environment》2012,35(5):966-981
We investigated whether the degree of light inhibition of leaf respiration (R) differs among large Eucalyptus saligna grown in whole‐tree chambers and exposed to present and future atmospheric [CO2] and summer drought. Associated with month‐to‐month changes in temperature were concomitant changes in R in the light (Rlight) and darkness (Rdark), with both processes being more temperature dependent in well‐watered trees than under drought. Overall rates of Rlight and Rdark were not significantly affected by [CO2]. By contrast, overall rates of Rdark (averaged across both [CO2]) were ca. 25% lower under drought than in well‐watered trees. During summer, the degree of light inhibition of leaf R was greater in droughted (ca. 80% inhibition) than well‐watered trees (ca. 50% inhibition). Notwithstanding these treatment differences, an overall positive relationship was observed between Rlight and Rdark when data from all months/treatments were combined (R2 = 0.8). Variations in Rlight were also positively correlated with rates of Rubisco activity and nitrogen concentration. Light inhibition resulted in a marked decrease in the proportion of light‐saturated photosynthesis respired (i.e. reduced R/Asat). Collectively, these results highlight the need to account for light inhibition when assessing impacts of global change drivers on the carbon economy of tree canopies. 相似文献
6.
Activation of Rubisco controls CO<Subscript>2</Subscript> assimilation in light: a perspective on its discovery 总被引:2,自引:0,他引:2
Jensen R 《Photosynthesis research》2004,82(2):187-193
CO2 fixation during photosynthesis is regulated by the activity of ribulose bisphosphate carboxylase (Rubisco). This conclusion
became more apparent to me after CO2-fixation experiments using isolated spinach chloroplasts and protoplasts, purified Rubisco enzyme, and intact leaves. Ribulose
bisphosphate (RuBP) pools and activation of Rubisco were measured and compared to 14CO2 fixation in light. The rates of 14CO 2 assimilation best followed the changes in Rubisco activation under moderate to high light intensities. RuBP pool sizes regulated
14
2 assimilation only in very high CO2 levels, low light and in darkness. Activation of Rubisco involves two separate processes: carbamylation of the protein and
removal of inhibitors blocking carbamylation or blocking RuBP binding to carbamylated sites before reaction with CO2 or O2.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
7.
Nonphotosynthetic CO(2) Fixation by Alfalfa (Medicago sativa L.) Roots and Nodules 总被引:1,自引:1,他引:0
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The dependence of alfalfa (Medicago sativa L.) root and nodule nonphotosynthetic CO2 fixation on the supply of currently produced photosynthate and nodule nitrogenase activity was examined at various times after phloem-girdling and exposure of nodules to Ar:O2. Phloemgirdling was effected 20 hours and exposure to Ar:O2 was effected 2 to 3 hours before initiation of experiments. Nodule and root CO2 fixation rates of phloem-girdled plants were reduced to 38 and 50%, respectively, of those of control plants. Exposure to Ar:O2 decreased nodule CO2 fixation rates to 45%, respiration rates to 55%, and nitrogenase activities to 51% of those of the controls. The products of nodule CO2 fixation were exported through the xylem to the shoot mainly as amino acids within 30 to 60 minutes after exposure to 14CO2. In contrast to nodules, roots exported very little radioactivity, and most of the 14C was exported as organic acids. The nonphotosynthetic CO2 fixation rate of roots and nodules averaged 26% of the gross respiration rate, i.e. the sum of net respiration and nonphotosynthetic CO2 assimilation. Nodules fixed CO2 at a rate 5.6 times that of roots, but since nodules comprised a small portion of root system mass, roots accounted for 76% of the nodulated root system CO2 fixation. The results of this study showed that exposure of nodules to Ar:O2 reduced nodule-specific respiration and nitrogenase activity by similar amounts, and that phloem-girdling significantly reduced nodule CO2 fixation, nitrogenase activity, nodule-specific respiration, and transport of 14C photoassimilate to nodules. These results indicate that nodule CO2 fixation in alfalfa is associated with N assimilation. 相似文献
8.
Rate of photosynthesis and activities of photosynthetic carbon reduction cycle enzymes were determined in pods (siliqua),
whereas rate of dark CO2 fixation, oil content and activities of enzymes involved in dark CO2 metabolism were measured in seeds ofBrassica campestris L. cv. Toria at different stages of pod/seed development. The period between 14 and 35 days after anthesis corresponded to
active phase of seed development during which period, seed dry weight and oil content increased sharply. Rate of pod photosynthesis
and activities of photosynthetic carbon reduction cycle enzymes were maximum in younger pods but sufficiently high levels
were retained up to 40 days after anthesis. The rate of dark14CO2 fixation in seeds increased up to 21 days after anthesis and declined thereafter but maintaining sufficiently high rates
till 35 days after anthesis. Similarly various enzymes viz., phosphoenolpyruvate carboxylase, NAD+-malate dehydrogenase and NADP+-malic enzyme, involved in dark CO2 metabolism retained sufficient activities during the above period. These enzyme activities were more than adequate to maintain
the desired supply of malate which mainly arises from dark CO2 fixation in seeds and further translocated to leucoplasts for onward synthesis of fatty acids. Enzyme localization experiments
revealed phosphoenolpyruvate carboxylase and enzymes of sucrose metabolism to be present only in cytosol, whereas enzymes
of glycolysis were present both in cytosolic and leucoplastic fractions. These results indicated that oil synthesis in developingBrassica seeds is supported by pod photosynthesis and dark CO2 fixation in seeds as the former serves as the source of sucrose and the latter as a source of malate 相似文献
9.
Estimation of Primary Productivity by Chlorophyll a in vivo Fluorescence in Freshwater Phytoplankton
Primary productivity in marine waters is widely estimated by the measurements of 14C incorporation, the underwater light climate, and the absorption spectra of phytoplankton. In bio-optical models the quantum efficiency of carbon fixation derived from 14C incorporation rates, the photosynthetically absorbed radiation derived from the underwater light climate, and the phytoplankton absorption spectra are used to calculate time- and depth-integrated primary productivity. Due to the increased sensitivity of commercially available fluorometers, chlorophyll a in vivo fluorescence became a new tool to assess the photosynthetic activity of phytoplankton. Since fluorescence data yield only relative photosynthetic electron transport rates, a direct conversion into absolute carbon fixation rates is not possible. Here, we report a procedure how this problem can be adressed in freshwater phytoplankton. We adapted a marine bio-optical model to the freshwater situation and tested if this model yields realistic results when applied to a hypertrophic freshwater reservoir. Comparison of primary productivity derived from 14C incorporation to primary productivity derived from Chl a fluorescence showed that the conversion of fluorescence data into carbon fixation rates is still an unsolved problem. Absolute electron transport rates calculated from fluorescence data tend to overestimate primary production. We propose that the observed differences are caused mainly by neglecting the package effect of pigments in phytoplankton cells and by non-carbon related electron flow (e.g., nitrogen fixation). On the other hand, the 14C incorporation rates can be artificially influenced by "bottle effects", especially near the water surface, where photoinhibition, photorespiration, and Mehler reaction can play a major role. 相似文献
10.
Summary
14CO2-fixation rates in green carrot callus cultres (about 35 g chlorophyll/g fresh wt) were determined in gaseous and liquid media using a range of light intensities and CO2 concentrations. Main products of light-dependent CO2-fixation were sucrose, alanine, glutamine, serine/glycine and malic acid. In darkness, glutamine and malic acid were formed.Light CO2-fixation rates were about ten times higher than dark fixation rates and reached 50–90 mol/mg chlorophyll/h in 10000 lux, 1% CO2 in air. Net O2-evolution by the tissue was demonstrated polarographically under these conditions. Light CO2-fixation rates were linearly related to chlorophyll levels while dark fixation was independent of chlorophyll content. Lowered O2 partial pressures in gaseous conditions increased 14CO2-fixation rates. Ribulose diphosphate carboxylase and phosphoenol pyruvate carboxylase activities and their distribution in subcellular fractions were examined.When carrot tissue cultures were grown for two or four weeks on agar media lacking a carbohydrate source, in 10000 lux and 1% CO2 in either air or N2, dry weight increases were obtained although chlorophyll levels eventually declined. 相似文献
11.
Temperature effects on malic-acid efflux from the vacuoles and on the carboxylation pathways in crassulacean-acid-metabolism plants 总被引:5,自引:0,他引:5
The studies described in the paper were conducted with tissue slices of Crassulacean acid metabolism (CAM) plants floating in isotonic buffer. In a first series of experiments, temperature effects on the efflux of [14C]malate and14CO2 were studied. An increase of temperature increased the efflux from the tissue in a non-linear manner. The efflux was markedly influenced also by the temperatures applied during the pretreatment. The rates of label export in response to the temperature and the relative contributions of14CO2 and [14C]malate to the label export were different in the two studied CAM plants (Kalanchoë daigremontiana, Sempervivum montanum). In further experiments, temperature response of the labelling patterns produced by14CO2 fixation and light and darkness were studied. In tissue which had accumulated malate (acidified state) an increase of temperature decreased the rates of dark CO2 fixation whilst the rates of CO2 fixation in light remained largely unaffected. An increase of temperature shifted the labelling patterns from a C4-type (malate being the mainly labelled compound) into a C3-type (label in carbohydrates). No such shift in the labelling patterns could be observed in the tissue which had depleted the previously stored malate (deacidified state). The results indicate that in the acidified tissue the increase of temperature increases the efflux of malate from the vacuole by changing the properties of the tonoplast. It is assumed that the increased export of malic acid lowers the in-vivo activity of phosphoenol pyruvate carboxylase by feedback inhibition.Abbreviations CAM
Crassulacean acid metabolism
- FW
fresh weight
- PEPCase
phosphoenolpyruvate carboxylase
Dedicated to Professor O.L. Lange, Würzburg, on the occasion of his 60th birthday 相似文献
12.
Activities of key enzymes of Calvin cycle and C4 metabolism, rate of 14CO2 fixation in light and dark and the initial products of photosynthetic 14CO2 fixation were determined in flag leaf and different ear parts of wheat viz. pericarp, awn and glumes. Compared to the activities of RuBP carboxylase and other Calvin cycle enzymes viz. NADP-glyceraldehyde-3-phosphate dehydrogenase, NAD-glyceraldehyde-3-phosphate dehydrogenase and ribulose-5-phosphate kinase, the levels of PEP carboxylase and other enzymes of C4 metabolism viz. NADP-malate dehydrogenase, NAD-malate dehydrogenase, NADP-malic enzyme, NAD-malic enzyme, glutamate oxaloacetate transaminase genase, NADP-malic enzyme, NAD-malic enzyme, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase, were generally greater in ear parts than in the flag leaf. In contrast to CO2 fixation in light, the various ear parts incorporated CO2 in darkness at much higher rates than flag leaf. In short term assimilation of 14CO2 by illuminated ear parts, most of the 14C was in malate with less in 3-phosphoglyceric acid, whereas flag leaves incorporated most into 3-phosphoglyceric acid. It seems likely that ear parts have the capability of assimilating CO2 by the C4 pathway of photosynthesis and utilise PEP carboxylase for recapturing the respired CO2. 相似文献
13.
Uptake of bicarbonate ion in darkness by isolated chloroplast envelope membranes and intact chloroplasts of spinach 总被引:8,自引:7,他引:1
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Poincelot RP 《Plant physiology》1974,54(4):520-526
Bicarbonate uptake by isolated chloroplast envelope membranes and intact chloroplasts of spinach (Spinacia oleracea L. var. Viroflay) in darkness exhibited a similar dependency upon temperature, pH, time, and concentrations of isolated or attached envelope membranes. This similarity in uptake properties demonstrates the usefulness of the envelope membranes for the study of chloroplast permeability. Maximal rates for dark HCO3- uptake by isolated envelope membranes and intact chloroplasts were more than sufficient to account for the maximal rates of photosynthetic CO2 fixation observed with intact chloroplasts. The active species involved in the uptake process was found to be HCO3- and not CO2. The significance of HCO3- uptake and its relationship to carbonic anhydrase and ribulose diphosphate carboxylase is discussed. Conditions for maximal HCO3- uptake in darkness by intact chloroplasts were found to be similar to those required for maximal photosynthetic CO2 fixation, suggesting that HCO3- uptake by the envelope membrane may regulate photosynthetic CO2 fixation. 相似文献
14.
Dark Carbon Dioxide Fixation under Aerobic and Anaerobic Conditions in Maize Leaves after Preillumination in the Absence of Oxygen: Ribulose 1,5-Bisphosphate Can Serve as a Primary Acceptor of Carbon Dioxide 总被引:2,自引:2,他引:0
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Creach E 《Plant physiology》1979,63(4):788-791
When dark 14CO2 fixation in maize leaves was carried out under anaerobic conditions after preillumination in the absence of O2, the 14C incorporation in aspartic acid was transient; its maximum level was very low compared with that of malic acid. The addition of 5% O2 during the dark fixation period increased the total uptake of 14CO2 and the 14C incorporation into aspartic acid. 相似文献
15.
Jacob Pardew Macarena Blanco Pimentel Etienne Low‐Decarie 《Ecology and evolution》2018,8(8):4292-4302
Rising atmospheric CO2 and ocean acidification are fundamentally altering conditions for life of all marine organisms, including phytoplankton. Differences in CO2 related physiology between major phytoplankton taxa lead to differences in their ability to take up and utilize CO2. These differences may cause predictable shifts in the composition of marine phytoplankton communities in response to rising atmospheric CO2. We report an experiment in which seven species of marine phytoplankton, belonging to four major taxonomic groups (cyanobacteria, chlorophytes, diatoms, and coccolithophores), were grown at both ambient (500 μatm) and future (1,000 μatm) CO2 levels. These phytoplankton were grown as individual species, as cultures of pairs of species and as a community assemblage of all seven species in two culture regimes (high‐nitrogen batch cultures and lower‐nitrogen semicontinuous cultures, although not under nitrogen limitation). All phytoplankton species tested in this study increased their growth rates under elevated CO2 independent of the culture regime. We also find that, despite species‐specific variation in growth response to high CO2, the identity of major taxonomic groups provides a good prediction of changes in population growth and competitive ability under high CO2. The CO2‐induced growth response is a good predictor of CO2‐induced changes in competition (R2 > .93) and community composition (R2 > .73). This study suggests that it may be possible to infer how marine phytoplankton communities respond to rising CO2 levels from the knowledge of the physiology of major taxonomic groups, but that these predictions may require further characterization of these traits across a diversity of growth conditions. These findings must be validated in the context of limitation by other nutrients. Also, in natural communities of phytoplankton, numerous other factors that may all respond to changes in CO2, including nitrogen fixation, grazing, and variation in the limiting resource will likely complicate this prediction. 相似文献
16.
N(2)-Fixation by Freshly Isolated Nostoc from Coralloid Roots of the Cycad Macrozamia riedlei (Fisch. ex Gaud.) Gardn
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Nitrogenase (EC 1.7.99.2) activity (acetylene reduction) and nitrogen fixation (15N2 fixation) were measured in cyanobacteria freshly isolated from the coralloid roots of Macrozamia riedlei (Fisch. ex Gaud.) Gardn. Light and gas phase oxygen concentration had marked interactive effects on activity, with higher (up to 100-fold) rates of acetylene reduction and 15N2 fixation in light. The relationship between ethylene formation and N2-fixation varied in the freshly isolated cyanobacteria from 4 to 7 nanomoles of C2H4 per nanomole 15N2. Intact coralloid roots, incubated in darkness and ambient air, showed a value of 4.3. Maximum rates of nitrogenase activity occurred at about 0.6% O2 in light, while in darkness there was a broad optimum around 5 to 8% O2. Inhibition of nitrogenase, in light, by pO2 above 0.6% was irreversible. Measurements of light-dependent O2 evolution and 14CO2 fixation indicated negligible photosynthetic electron transport involving photosystem II and, on the basis of inhibitor studies, the stimulatory effect of light was attributed to cyclic photophos-phorylation. Nitrogenase activity of free-living culture of an isolate from Macrozamia (Nostoc PCC 73102) was only slightly inhibited by O2 levels above 6% O2 and the inhibition was reversible. These cells showed rates of light-dependent O2 evolution and 14CO2 fixation which were 100- to 200-fold higher than those by the freshly isolated symbiont. Furthermore, nitrogenase activity was dependent on both photosynthetic electron transport and photophosphorylation. These data indicate that cyanobacteria within cycad coralloid roots are differentiated specifically for symbiotic functioning in a microaerobic environment. Specializations include a high heterocyst frequency, enhanced permeability to O2, and a direct dependence on the cycad for substrates to support nitrogenase activity. 相似文献
17.
Fruiting structures of a number of legumes including chickpea are known to carry out photosynthetic CO2 assimilation, but the pathway of CO2 fixation and particularly the role of phosphoenolpyruvate carboxylase (EC 4.1.1.31) in these tissues is not clear. Activities of some key enzymes of the Calvin cycle and C4 metabolism, rates of 14CO2 fixation in light and dark, and initial products of photosynthetic 14CO2 fixation were determined in podwall and seedcoat (fruiting structures) and their subtending leaf in chickpea (Cicer arietinum L.). Compared to activities of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and other Calvin cycle enzyme, viz. NADP+-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13), NAD+-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) and ribulose-5-phosphate kinase (EC 2.7.1.19), the levels of phosphoenolpyruvate carboxylase and other enzymes of C4 metabolism viz. NADP+-malate dehydrogenase (EC 1.1.1.82), NAD+-malate dehydrogenase (EC 1.1.1.37), NADP+ malic enzyme (EC 1.1.1.40), NAD+-malic enzyme (EC 1.1.1.39), glutamate oxaloacetate transaminase (EC 2.6.1.1) and glutamate pyruvate transaminase (EC 2.6.1.2), were generally much higher in podwall and seedcoat than in the leaf. Podwall and seedcoat fixed 14CO2 in light and dark at much higher rates than the leaf. Short-term assimilation of 14CO2 by illuminated fruiting structures produced malate as the major labelled product with less labelling in 3-phosphoglycerate, whereas the leaf showed a major incorporation into 3-phosphoglycerate. It seems likely that the fruiting structures of chickpea utilize phosphoenolpyruvate carboxylase for recapturing the respired carbon dioxide. 相似文献
18.
R. Lignell 《Hydrobiologia》1993,254(3):159-167
During the phytoplankton succession in 1984 and 1985, the effect of fluctuating light on algal photosynthesis (incorporation
of 14C, acidified water sample) was studied in the northern Baltic. Bottles were mounted on moving racks that mimicked vertical
transport caused by Langmuir circulations in the trophogenic layer.
Assuming that the photoinhibition observed near the surface in fixed-depth incubations (from 1 to 8% of integral photosynthesis)
was avoided in cycled samples, vertical cycling conducted around noon resulted in on average 10% lower photosynthesis than
fixed-depth incubations (n = 17). This difference lies within the 5% confidence limits of the measurement, and hence it was concluded that the lack
of short-term fluctuations in light associated with the vertical circulation of natural phytoplankton communities does not
seriously bias conventional in situ
14CO2 fixation measurements performed at fixed depths in the study area. 相似文献
19.
A rapid method to determine the CO2/O2 specificity factor of ribulose 1,5-bisphosphate carboxylase/oxygenase is presented. The assay measures the amount of CO2 and O2 fixation at varying CO2/O2 ratios to determine the relative rates of each reaction. CO2 fixation is measured by the incorporation of the moles of14CO2 into 3-phosphoglycerate, while O2 fixation is determined by subtraction of the moles of CO2 fixed from the moles of RuBP consumed in each reaction. By analyzing the inorganic phosphate specifically hydrolyzed from RuBP under alkaline conditions, the amount of RuBP present before and after catalysis by rubisco can be determined. 相似文献
20.
Hans W. Paerl 《Journal of phycology》1994,30(5):790-799
The aggregate-forming, nonheterocystous, filamentous blue-green alga (cyanobacteria) Trichodesmium spp. is a widespread and important planktonic N2 fixer and primary producer in tropical and subtropical oceans. It is unique among nonheterocystous genera because it conducts N2 and CO2 fixation (O2 evolution) simultaneously; a notable achievement, because O2 is a potent inhibitor of N2 fixation. Spatial and temporal CO2 fixation patterns were examined in trichomes and aggregates from natural and cultured populations, utilizing microautoradiographic detection of 14CO2 incorporation. Parallel N2 fixation (acetylene reduction) measurements were also made. Diel N2 and CO2 fixation patterns were similar, with co-optimization of both processes near midday. Microautoradiographs revealed several trichome-level 14CO2 incorporation patterns: 1)uniform, heavy labeling, 2)uniform, light labeling, 3) heavier labeling in distal as opposed, to proximal regions, and 4) virtually no labeling throughout. Similar patterns were observed in natural and cultured populations. Given previous immunochemical findings that N2 fixation potential is widespread in Trichodesmium spp. trichomes and aggregates, current results suggest a high degree of individuality, and possibly a “division of labor” in terms of CO2 fixation, among trichomes comprising active N2-fixing aggregates. Segregation of photosynthesis within and among trichomes facilitates simultaneous N2 and CO2 fixation in Trichodesmium spp. trichomes and aggregates. 相似文献