共查询到20条相似文献,搜索用时 31 毫秒
1.
Changes in photosynthetic carbon metabolism during the glucosebleaching of Chlorella protothecoides cells were investigatedusing NaH14CO3 as tracer. Several hours after incubating thegreen algal cells in the glucose medium in the dark, the ratesof 14C-incorporation into glucose polymers and sucrose decreasedand the incorporation into the lipid fraction (fatty acids)greatly increased. At this stage, the rate of photosynthetic14CO2 fixation and the chlorophyll content were practicallythe same as in the starting green cells. Afterwards, the photosyntheticcapacity and chlorophyll content continued to decrease throughoutthe experimental period. In contrast, when photosynthetic 14CO2fixation of green cells was carried out in the medium containingglucose, the rate of 14C-incorporation into glucose polymersincreased, though there was no change in the incorporationsinto sucrose and the lipid fraction.
1Part of this investigation was reported at the Conference "ComparativeBiochemistry and Biophysics of Photosynthesis" (Japan-U.S. CooperativeScience Program) held at Hakone, Japan in 1967.
2Present address: Faculty of Agriculture, Tamagawa University,Machida-shi, Tokyo, Japan. (Received June 10, 1974; ) 相似文献
2.
The 14C-metabolite distribution pattern following 14C2H4 metabolismin intact pea seedlings (Pisum sativum L.) was determined undervarious conditions. After a 24 hr exposure to 14C2H4, the majorityof 14C-metabolites were water-soluble (6070%) with lesseramounts in the protein (1015%), lipid (1%), and insoluble(12%) fractions. Ion exchange chromatography of the water-solublecomponents into basic, neutral, and acidic fractions revealeda 50 : 40 : 10 distribution, respectively. Chromatography ofthe neutral fraction revealed two regions of radioactivity (Rf=0.38)and 0.63 which did not cochromatograph with twenty-two knownsugars or neutral metabolites. Chromatograms of the basic fractioncontained 3 regions of radioactivity. Similar distribution patternswere noted when 14C2H4 exposure was followed by a 6 hr air chaseor when 5% CO2, an antagonist of ethylene action, was presentduring the exposure. Marked differences in the 14C-metabolite distribution patternswere obtained when 14CO2 was substituted for 14C2H4. These resultsindicate that the metabolic pathway involved in ethylene metabolismis different from that involved in intermediary carbon metabolism.
1 Contribution No. 2338 from Central Research and DevelopmentDepartment, Experimental Station, E. I. du Pont de Nemours andCompany, Wilmington, Delaware. (Received June 28, 1976; ) 相似文献
3.
Photosynthetic assimilation of exogenous 14CO2 and H14CO3by the aquatic angiosperm Potamogeton lucens L. is reported.Equivalent maximum rates of assimilation (1.5 µmol s1m2) were obtained in the presence of saturating levelsof 14CO2 (1.0 mol m3, pH 5.3) or H14CO3 (1.5 molm3, pH, 9.2). Under subsaturating 14CO2 levels, bothgaseous diffusion and H14CO3 transport were shown tooperate simultaneously, such that maximal photosynthetic rateswere established. An induction lag of approximately 3 min was observed when exogenous14CO2 was assimilated. A longer lag of approximately 12 minwas required, however, before linear assimilation rates wereestablished when H14CO3 acted as the carbon source. The light-activatedH14CO3 transport system was found to be quite labile.A brief (5 min) dark treatment returned the system to the inactivestate. Bicarbonate transport was shown to be competitively inhibitedby CO32ions. The possibility is discussed that this formof inhibition may be common to many HCO3 assimilators. Preliminary polar cation transport studies (from lower to upperleaf surface) indicated an almost exact one to one relationshipbetween the rates of Na+ influx and efflux and H14CO3assimilation. The possible relationship(s) between these transportprocesses and the requirement for electrical neutrality is brieflydiscussed. 相似文献
4.
Radioactive starch, glucose and fructose have been preparedfrom tobacco leaves after assimilation of C14O2. The apparatusused for photosynthesis consisted of a shallow Perspex leafchamber connected to a closed gas system, in which C14O2 wasgenerated from BaC14O2. Six leaves, area 14 to 18 sq. dm. whenexposed to bright sunlight with an initial CO2 concentrationof 8 to 10 per cent., assimilated 3.35 g. of C14O2 in 8 to 10hours. At least 80 per cent. of the C14O2 supplied appearedin the leaves as starch and sugar and over 80 per cent. of theradioactivity was accounted for in these carbohydrates. Thespecific activity per m. atom of carbon of the isolated productswas 85 to 90 per cent. of that of the C14O2. Small amounts ofradioactive carbon were also incorporated in the leaf proteinand in the celluose, hemicellulose and polyuronides. 相似文献
5.
- The capacity of light-enhanced dark fixation of 14CO2 from theambient atmosphere decayed following time-course characteristicsof a first-order reaction (half-life, 12 min). The levelof phosphoenolpyruvate in maize leaves under CO2-free air didnot decrease in the dark subsequent to preillumination. Theseresults indicate that phosphoenolpyruvate carboxylase is activatedin light and quickly inactivated in the following darkness.
- Removal of oxygen from the atmosphere did not exert any effecton the products of light-enhanced dark fixation of 14CO2 providedfrom the atmosphere, the major labeled compounds being malateand aspartate. This confirms that the transfer of carboxyl carbonof C4-acids to form 3-phosphoglycerate is light-dependent.
- WhenNaH14CO3 solution was vacuum-infiltrated through vasculartissuesof maize leaves, the main initial photosynthetic 14CO2fixationproducts were phosphate esters. This indicates thatby thistechnique, 14CO2 could be directly provided to the bundlesheathcells, and was fixed via the reductive pentose phosphatecycle.On the other hand, the main initial 14CO2-fixation productswere malate and aspartate even when 14CO2 was provided throughvascular tissues in the dark immediately following preillumination.The possible regulatory mechanisms underlying the above findingsare discussed.
6.
Most of the 14C added as glucose to carbohydrate-starved cellsof Chlorella Vulgaris can be recovered as alcohol-soluble compoundsor as polysaccharide. Only 5I6 per cent., depending onthe position of 14C in the glucose supplied, is released ascarbon dioxide. Similar results were obtained with Chlorellapyrenoidosa and Ankistrodesmus. The labelled alcohol-solublecompounds in Chlorella vulgaris include amino-acids, particularlyglutamic acid, aspartic acid, and alanine, and, when glucose-I-14Cis metabolized, the amount of 14C recovered in these amino-acidsis about the same as that recovered as carbon dioxide. Degradationof the glucose incorporated into polysaccharide shown that theC1 and C6 atoms of glucose rapidly interchange when in the cells.The bearing of these results on attempts to estimate the relativeimportance of different pathways of glucose breakdown is discussed. 相似文献
7.
Maximum fixation rates of 120 and 60 pmol cm2 s 1wereobtained when exogenous carbon was supplied as 1CO2 and H14CO3respectively. These values are considerably higher than thosepreviously reported for this species. A kinetic analysis wasperformed on this data. Substrate saturation in the concentrationrange 1.01.5 mM was observed for both CO2 and HCO3 In the presence of exogenous CO2, a linear relationship wasobserved between light intensity and fixation while the HCO3relationship was slightly sigmoidal. Fixation saturated at intensitiesof 1520 W m2 and 1315 W m2 for exogenous14CO2 and H14CO3respectively. The presence, in this species, of an extremely active HCO3transport system, situated in the plasmalemma, demonstratesthat when alkaline solutions are employed the involvement ofthis ion cannot be ignored during electrical studies on thismembrane. The maximum H14CO3 influxes obtained duringthis study are the largest ionic fluxes measured for any Characeanspecies. It was demonstrated that CO2 for fixation can be supplied simultaneouslyby gaseous diffusion and HCO3 transport (cf. Raven, 1968).Inhibition of H14CO3 influx was observed in the presenceof Tris, Tricine, and borate buffers, and CO32 alsoappeared to act as a strong inhibitor. The possible mechanism(s)by which this inhibition occurs is discussed. 相似文献
8.
de S. WAIDYANATHA U. P.; KEYS A. J.; WHITTINGHAM C. P. 《Journal of experimental botany》1975,26(1):27-32
Segments of wheat leaves were supplied in the light with 14C-labelledserine or glucose in atmospheres containing different concentrationsof O2 and zero or 350 parts/106 CO2. Some O2 was necessary forsucrose synthesis from either serine or glucose but sucrosesynthesis from glucose depended on reactions with a high affinityfor O2 whereas sucrose synthesis from serine depended both onreactions with high and low affinities for O2. In the presenceof CO2 sucrose synthesis from serine was decreased when theO2 concentration was increased from 20 to 80% by volume andCO2 was liberated; sucrose synthesis from glucose was almostunaffected by the same change in conditions. Also, in an atmospherecontaining 80% O2 and 350 parts/106 CO2, radioactivity from[14C]serine, was incorporated into glycine. This was not truefor glucose feeding. Hence glucose provides a substrate forsucrose synthesis but not for photorespiration whereas serineis used for both processes in the presence of CO2; in the absenceof CO2 glucose provides substrate for both sucrose synthesisand photorespiration and serine metabolism to sucrose is restricted. 相似文献
9.
Tobacco leaves depleted of starch, were detached and allowedto assimilate equal amounts of 14CO2 and 12CO2in succession,and vice versa. Distribution of radioactivity in starch, andsugars was determined after assimilation and after disks cutfrom the leaves had been kept in darkness for times up to 40hours. The amount and activity of the CO2 was also determined.14C and 12C were incorporated in equal amounts into starch independentlyof the order in which they were supplied. In contrast sucrosehad high activity 14C was given last, and hexose a low one.The reverse was true when 12C was given last. Activity of respiratoryCO2 was slightly higher when 14C was assimilated last as comparedwith 12C. In the dark only 14C or 12C was at first lost fromstarch, in accordance or removal of discrete layers. Analyticalresults show that starch is the main respiratory substrate andto account for the redistribution of radioactivity in passageto CO2 it is concluded that sucrose occurs at two sites separatedinter-or intra-cellularly, one of which is in equilibrium withthe system intrconverting starch and CO2 and at the other hexosesare produced by inversion. A starch-like polysaccharide is formedduring assimilation which persists in the dark and there isa significant contribution to respiration of carbon from non-carbohydratesources when leaf disks are kept on the dark. 相似文献
10.
A study was made of the incorporation of 14C by intact leavesof Coffea arabica (cultivars Mundo Novo, Catuai, 113013,and H 65862) and Coffea canephora (cultivar Guarini)supplied with gas mixtures containing 14CO2 under controlledconditions. Samples of the leaves were combusted and the 14Cin the CO2 produced measured using a liquid scintillation counter.The results were used to estimate photosynthetic rates. Theeffects of changing the partial pressures of O2 and CO2 on thephotosynthetic rate were studied and estimates made of the CO2compensation point and photorespiration. The data obtained show differences between the mean net photosyntheticrates of the C. arabica cultivars (6·14 mg CO2 dm2h1) and the mean rate for the C. canephora cultivar (3·96mg CO2 dm2 h1). The cultivar of the latter speciesphotorespired more rapidly than the cultivar Catuai of C. arabica.Rates of photosynthesis in coffee measured using the 14CO2 methodwere similar to rates obtained by others using an infrared gasanalyser. The 14CO2 method proved to be reliable for photosyntheticmeasurements and the apparatus is suitable for use in fieldconditions. 相似文献
11.
Twenty-four hours after leaf 3 of a plant of Lolium multiflorumLam, was supplied with a droplet of 14C-urea and the plant enclosedin a polyethylene bag with an untreated plant, there were significantamounts of radiocarbon recovered from the untreated plant. Theleaf treated with 14C-urea was the major source of 14C leakagebut significant losses were also recorded from other parts ofthe plant. Reducing the humidity within the bag decreased theamount of 14CO2 which escaped. Losses of radiocarbon from CO2-treated plants were very low compared with those from urea-treatedplants but the pattern of assimilate distribution within thetwo types of plants was very similar. The possible causes ofthese effects are considered and the usefulness of 14C-ureaas a source of 14CO2 discussed. 相似文献
12.
Time courses of photosynthetic 14CO2 fixation and its simulationare presented for Chlorella cells grown under low CO2 concentration(low-CO2 cells) and subsequently exposed to 0.2 mM NaH14CO3or 130 ppm 14CO2 in the presence or absence of carbonic anhydrase(CA) in the suspending medium. It was shown that Chlorella cells utilized only free CO2 whenNaHCO3 was given in the presence or absence of CA, or when CO2was bubbled in the absence of CA. However, the present simulationindicated that both CO3 and HCO3 were utilized when CO2was given in the presence of CA. Based on these results, weconcluded that 1) Chlorella cells absorb only free CO2 and 2)this gas is provided to algal cells in two ways, i.e., by directand indirect CO2 supply. Usually, the dissolved CO2 is directlyutilized by the algal cells (direct supply of CO2). However,when the concentration of dissolved CO2 is extremely low andwhen there is CA, CO2 reconverted from HCO3 is also utilizedby Chlorella cells (indirect supply of CO2). The utilizationof HCO3 indicated by the above simulation was explainedby the indirect supply of CO2. We further assumed that the indirectsupply of CO2 to ribulose 1,5-bisphosphate carboxylase occursmainly in the chloroplasts of low-CO2 cells containing highCA. Thus, under low CO2 concentrations, low-CO2 cells can carryout more efficient CO2 fixation than high-CO2 cells, resultingin the lower apparent Km(CO2).
3Department of Biology, Faculty of Science, Niigata University,Niigata, Japan. (Received April 2, 1980; ) 相似文献
13.
Previous studies have demonstrated that when cells of Chlorellaprotothecoides are incubated in a medium containing glucosebut no nitrogen source, they are profoundly bleached with degenerationof chloroplast structure and photosynthetic activity. When anitrogen source (urea) is added to the glucose medium, bleachingof algal cells is greatly suppressed. In this work the metabolismof glucose in the process of glucose-induced bleaching was studiedusing 14C-glucose as tracer. Changes in algal cell activityfor 14CO2-evolution and 14C-incorporation into various cellularsubstances from 14C-glucose were followed. Most conspicuouswere increases in cellular activities for assimilating 14C-glucoseinto lipids (fatty acids) and glucose polymer. When urea wasadded to the glucose medium, the incorporation of 14C by algalcells into fatty acids was greatly reduced, while the assimilationof 14C into glucose polymer was increased. These and previous observations suggest that the formation oflarge amounts of lipids (fatty acids) probably is causally relatedto the induction of algal cell bleaching. (Received March 5, 1969; ) 相似文献
14.
GORDON A. J.; RYLE G. J. A.; MITCHELL D. F.; POWELL D C. E. 《Journal of experimental botany》1985,36(5):756-769
Experiments are described which examine the flux of photosyntheticassimilates from leaves to nodules of soyabean during N2 fixation.The first part, where the respiratory efflux of 14CO2 by noduleswas used as a means of assessing the import of labelled photosynthatefrom leaves, shows that most 14CO2 loss from nodulated rootsis due to the metabolic activity of nodules. Much less photosynthatewas imported by nodules if the metabolic activity associatedwith N2 fixation was inhibited by low O2 concentration. The second part describes the chemical fate of current photosynthateas it is utilized by nodules. Labelled material was detectedin nodules within c.15 min of supplying 14CO2 to the leaf. Thisrose to a maximum at c.70 min before declining by 85% withinthe following 4 h. Most (80%) 14carbon imported by nodules waseither lost as respiratory 14CO2 or re-exported as productsof N2 fixation. Ten per cent of imported carbon was found asstructural material and 10% as starch. Of the 14C soluble in ethanol, most was found in the neutralfraction (80% declining to 50% as sucrose) with smaller amountsas amino acids, organic acids (each category rising from 10%to 20%) and phosphate esters (<5%). Comparison of the distribution of 14C among amino acids, amidesand ureides in the nodules with that of xylem exudates indicatedthat selected compounds were exported from nodules. The 14Cdata indicate that c.80% of the nitrogen exported from noduleswas in the form of ureides (mainly allantoic acid) and only1012% as amides. Key words: Nodules, 14C-photosynthate, Respiration, Carbon flux 相似文献
15.
The CO2 compensation point at 25 °C and 250 µEinsteinsm2 s1 wasmeasured for 27 bryo-phyte species, andwas found to be in the range of 45160 µl CO2 I1air. Under the same conditions Zea mays gave a value of 11 µlI1 and Horde um vulgare 76 µI1. The rate of loss of photosyntheticallyfixed 14CO2 in the light and dark in six bryophytes (three mosses,two leafy liverworts, one thalloid liverwort) was determinedin CO2-free air and 100% O2. The rate of 14CO2 evolution inthe light was less than that in the dark in CL2-free air, butin 100% O2 the rate in the light increased, so that in all butthe leafy liverworts it was greater than that in the dark. Raisingthe temperature tended to increase the rate of 14CO2 evolutioninto CO2-free air both in the light and dark, so that the light/dark(L/D) ratio did not greatly vary. The lower rate of loss of14CO2 in the light compared tothe dark could be due to partialinhibition of dark respiration reactions in thelight, a low rate of glycolate synthesis and oxidation, or partialreassimilation of the 14CO2 produced, or a combination of someor all of these factors. 相似文献
16.
When Chlorella oulgaris ll h cells grown in air containing 4%CO2 (high-CO2 cells) were given low concentrations of14CO2 (<150ppm), the initial rate of photosynthetic 14CO2 fixation wasvery low and linear 14CO2 fixation was observed after an inductionperiod which lasted for ca. 45 min. No such induction period was observed when high-CO2 cells weregiven high concentrations of 14CO2 (10,000 ppm) or when IOW-CO2cells were given either low or high concentrations of 14CO2,supporting the observations by Briggs and Whittingham (l). However,irrespective of CO2 concentrations during growth and of 14CO2concentrations during the experiments, most of the 14C was incorporatedinto phosphate esters during the initial periods of photosynthetic14CO2 fixation. These results are in sharp contrast to the reportby Graham and Whittingham (4).
1 Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received June 30, 1979; ) 相似文献
17.
Carbon Loss from the Roots of Forage Rape (Brassica napus L.) Seedlings Following Pulse-labelling with 14CO2 总被引:1,自引:0,他引:1
The loss of organic material from the roots of forage rape (Brassicanapus L.,) was studied by pulse-labelling 25-d-old non-sterilesand-grown plants with 14CO2. The distribution of 14C withinthe plant was measured at 0, 6 and 13 d after labelling whilst14 C accumulating in the root-zone was measured at more frequentintervals. The rates of 14C release into the rhizosphere, andloss of 14CO2 from the rhizosphere were also determined. Thesedata were used to estimate the accumulative loss of 14C fromroots and loss respiratory 14CO2 from both roots and associatedmicro-organisms. Approximately 17-19% of fixed 14CO2 was translocatedto the roots over 2 weeks, of which 30-34% was released intothe rhizosphere, and 23-24% was respired by the roots as 14CO2. Of the 14C released into the rhizosphere, between 35-51%was assimilated and respired by rhizosphere micro-organisms.Copyright1993, 1999 Academic Press Brassica napus L., carbon loss, carbon partitioning, microbial nutrition, microbial respiration, forage rape, pulse-labelling, rhizodeposition, root respiration, sand culture 相似文献
18.
BECCARI E.; D'AGNOLO G.; MORPURGO G.; POCCHIARI F. 《Journal of experimental botany》1969,20(1):110-112
In Daucus carota cells cultivated in vitro, the ammonium ionstimulates the incorporation of radioactivity from labelledglucose and labelled pyruvate into CO2 and into the residueinsoluble in 60 per cent (v/v) ethanol. There is a higher 14CO2production from [6-14C2] glucose than from [6-14C] glucose.These results suggest a possible stimulation of glycolysis bythe ammonium ion. 相似文献
19.
The nature and rate of degradation of carboxyl-14C-labelledindol-3y1-acetic acid (IAA-[l-14C]) were studied in apple leaves.The labelled auxin was applied to the cut surface of the growingshoot after the apical part had been removed. The respiratoryCO2 absorbed by chromatographic paper as Na2CO3 then freed byphosphoric acid was quantitatively measured by an internal gascounter. It was found that the concentration of 14CO2 evolvedby leaves was 77 times higher in daylight than in darkness.The ratio of 14CO2/CO2 obtained from respiration from the uppersurface of leaf blades was two and seven times higher than thatfrom the lower surface after 15 and 30 h of daylight, respectively.No such differences were noticed in darkness. Similarly, thetotal radioactivity of leaf tissues tripled in daylight, presumablybecause of photosynthetic incorporation of radioactive CO2 evolvedduring decomposition of LAA. These facts demonstrate the photolyticcharacter of auxin decarboxylation in apple leaves. Prolongeddarkness seemed to provoke a large metabolite withdrawal fromleaves and, to some extent, to protect auxin against decarboxylation. 相似文献
20.
In experiments using radioactive carbon dioxide (14CO2) a comparisonwas made of the 14C-photoassimilate translocation potentialsof two normal leaved (genotype AfAfTlTl) and two mutant formsof Pisum sativum (pea). A 14CO2 administration method is describedthat permitted 14C-translocation studies to be conducted underfield conditions. One of the mutants available produced tendrils in place of leaves(afafTlTl). The other mutant studied was without tendrils buthad a much branched petiole with numerous relatively minuteleaflets (afaftltl). These mutants and the normal-leaved cultivarswith which they were compared were not isogenic lines. Lengthybackcrossing would be required before full assessment couldbe made of the possible agronomic value of such mutations. An interim evaluation of these mutants was based on 14C-distributionassays that were conducted 48 h after feeding 14CO2, to specifiedleaves. The indication was that in translocation terms the leafand pod had a well defined respective source and sink relationshipthat was independent of leaf morphology. In each case the podswhich constituted the major 14C sinks depended on which leafhad been fed 14CO2. With regard to sink specific activity asdefined by the quantity of 14C incorporated per unit dry weightof pod, the mutants were not significantly different from normal. The implication of these findings was that fundamental changesin pea leaf morphology could be made genetically without a markedeffect on the photoassimilate export potential of the leaf. 相似文献