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1.
Summary Activated carboxylase activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), as well as photosynthetic rates were measured for 42 species of freshwater and marine macrophytes. While the carboxylase activity varied greatly among the species investigated (0.2–12.5 mol CO2 mg–1 chlorophyll min–1), the submersed freshwater plants showed significantly lower activities than emergent, floating leaved or secondary submersed forms. The variability in photosynthetic rates correlated with the carboxylase activity only for the marine macroalgae, and their photosynthesis to carboxylase activity ratios were close to 1. These plants also had a consistently high inorganic carbon transport capability, and it is suggested that ribulose-1,5-bisphosphate carboxylase/oxygenase activity is an important internal factor regulating the photosynthetic capacity within this plant group where, apparently, the internal CO2 concentration is high and photorespiration is suppressed. Among the freshwater forms, it appears that their much lower inorganic carbon transport ability, rather than their carboxylase activity, limits the photosynthetic process.  相似文献   

2.
The effect of long-term exposure to elevated levels of CO2 on biomass partitioning, net photosynthesis and starch metabolism was examined in cotton. Plants were grown under controlled conditions at 350, 675 and 1000 l l-1 CO2. Plants grown at 675 and 1000 l l-1 had 72% and 115% more dry weight respectively than plants grown at 350 l l-1. Increases in weight were partially due to corresponding increases in leaf starch. CO2 enrichment also caused a decrease in chlorophyll concentration and a change in the chlorophyll a/b ratio. High CO2 grown plants had lower photosynthetic capacity than 350 l l-1 grown plants when measured at each CO2 concentration. Reduced photosynthetic rates were correlated with high internal (non-stomatal) resistances and higher starch levels. It is suggested that carbohydrate accumulation causes a decline in photosynthesis by feedback inhibition and/or physical damage at the chloroplast level.Abbreviations Ci internal CO2 concentration - Chl chlorophyll - DMSO dimethylsulfoxide - HSD honestly significant difference (procedure) - MCW methanolchloroform-water - Pi inorganic phosphate - S.E.M. standard error of mean  相似文献   

3.
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   

4.
During the first 8–12 days of cultivation in a nutrient solution containing IAA, inositol and kinetin freshly isolated carrot root explants develop into a chlorophyllous and photosynthetically active tissue culture. Electron microscopy, low temperature pigment absorption spectra and fluorescence induction profile recording as well as the determination of the activity of some enzymes (ribulosebisphosphate carboxylase, phosphoenolpyruvate carboxylase) and CO2-fixation experiments were carried out. Based on the results, a sequence of developmental stages of the photosynthetic system will be proposed. During the autotropic period from about the 20th day of culture onward the light reaction system of these tissue cultures is quite comparable to that of carrot leaves; however, some differences in the CO2-fixation mechanism were observed.  相似文献   

5.
W. Hüsemann 《Protoplasma》1981,109(3-4):415-431
Summary This communication reports the photoautotrophic growth of hormone and vitamin independent cell suspension cultures ofChenopodium rubrum. The transfer of cells from stationary growth into fresh culture medium results in a high protein formation, followed by an exponential phase of cell division, whereas the onset of rapid chlorophyll formation is delayed for 4 days. At the stage of most rapid cell division there is no net synthesis of starch and sugar. When the cells enter stationary growth, there is a progressive accumulation of chlorophyll, sugar, and starch.Photoautotrophic cell cultures assimilate about 80–90 mol CO2/mg chlorophyll X hour. Dark CO2 fixation is about 3.7% to 2.2% of the light values during exponential and stationary growth, respectively. As shown by short-term14CO2 fixation, CO2 is predominantly assimilated through ribulosebisphosphate carboxylase via the Calvin pathway. There is a significant increase in the14C label of C4 carboxylic acids in exponentially dividing cells as compared to cells from stationary growth. Thein vitro activity of phosphoenolpyruvate carboxylase and ribulosebisphosphate carboxylase is almost equal during exponential cell division. A decrease in cell division activity is accompanied by a significant change in the specific activities of both carboxylation enzymes. In non dividing cells from stationary growth the activity of ribulosebisphosphate carboxylase is greately enhanced and that of phosphoenolpyruvate carboxylase is reduced, documenting the development of carboxylation capacities typical for C3-plants.The experimental results provide evidence that phosphoenolpyruvate carboxylase activity might be regulated by ammonia and could be involved in anaplerotic CO2 fixation which supplies carbon skeletons of the citric acid cycle.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - EDTA ethylene-diamine-tetraacetic acid - FDP fructose bisphosphate - F-6-P fructose-6-phosphate - G-6-P glucose-6-phosphate - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - PGA 3-phosphoglyceric acid - PEP phosphoenolpyruvate - RuDP ribulosebisphosphate  相似文献   

6.
Phosphoenolpyruvate carboxykinase activity decreases when Euglena gracilis Z and ZR undergo light-induced chloroplast development in batch resting medium lacking utilizable organic carbon and CO2. This enzyme is present in heterotrophically grown cells (Briand et al. 1981) and assures gluconeogenesis. It was consistently more active in strain ZR. Decreased carboxykinase activities were accompanied by parallel increases in the activities of ribulose bisphosphate carboxylase and phosphoenolpyruvate carboxylase. The rates of O2 evolution in light were much lower than those of CO2 fixed simultaneously. The incorporation of 14CO2 into early C-4 dicarboxylic acids was higher in green cells than in etiolated cells, and it was even higher in green cells assayed in light in the presence of (DCMU). A hypothesis has been proposed, according to which there is a possible cooperation of phosphoenolpyruvate carboxylase in photosynthetic CO2 fixation, especially under conditions of limiting CO2.High temperatures (34° C) depress carboxylation enzyme activities to a greater extent than that of the carboxykinase without a great effect on cellular chlorophyll content. In the presence of 25 m DCMU, however, chlorophyll accumulation is reduced without any detectable changes in enzyme activities in the Z strain. The ZR strain displayed its characteristic resistance to DCMU.Abbreviations PEP phosphoenolpyruvate - RuBP ribulose bisphosphate - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea To whom all correspondence and reprint request should be addressed  相似文献   

7.
U. Lüttge  K. Fischer 《Planta》1980,149(1):59-63
Light-dependent CO-evolution by the green leaves of C3 and C4 plants depends on the CO2/O2 ratio in the ambient atmosphere. This and other physiological responses suggest that CO-evolution is a byproduct of photorespiration. At CO2/O2 ratios up to 10-3, the ratio of CO evolved: CO2 fixed in photosynthesis is significantly higher in C3 than in C4 plants. This discrepancy disappears when a correction is made for the CO2-concentrating mechanism in C4 photosynthesis, by which CO2-concentration at the site of ribulose-bis-phosphate carboxylase/oxygenase in the bundle sheaths is raised significantly as compared to the ambient atmosphere. Since the oxygenase function of this enzyme is responsible for glycolate synthesis, i.e., the substrate of photorespiration, this result seems to support the conclusion that CO-evolution is a consequence of photorespiration. CO-evolution may turn out to be a useful and rather straightforward indicator for photorespiration in ecophysiological studies.Abbreviations CAM crassulacean acid metabolism - CO net CO-evolution - CO2 net CO2-fixation - PEP-C phosphoenolpyruvate carboxylase - RubP-C ribulose-bisphosphate carboxylase/oxygenase Dedicated to Professor André Pirson on the occasion of his 70th birthday  相似文献   

8.
Summary The daily course of CO2 and H2O exchange in cladodes of Opuntia inermis was studied at four sites in Eastern Australia. On most occasions cladode water contents were high and nocturnal stomatal opening resulted in substantial uptake of CO2 and synthesis of about 130 equiv cm-2 of malic acid during the night. Under water stress nocturnal stomatal opening was confined to the latter part of the night and acid synthesis was reduced to about 40 equiv cm-2. Night temperature had little effect on acid synthesis, which responded primarily to rainfall and changed from the stressed condition within 2–3 days in irrigation experiments. On many occasions following summer rainfall stomata opened for 4 h in the late afternoon permitting net CO2 fixation which may contribute about 25% of the total carbon assimilated. This CO2 fixation was insufficient to have a marked impact on the 13C value of the Opuntia cladodes. CO2 fixation in the light occurred in conjunction with maximum dark CO2 fixation under mesic conditions. Dark CO2 fixation rates were 3 to 5 times greater than those recorded in desert cacti under favorable conditions. Relative growth rates calculated on the basic of CO2 exchange correspond to measured relative growth rates of 0.05 g g-1 dry wt day-1 which prevailed for 60–90 days in summer. The capacity for very active CO2 fixation in the dark and light following summer rainfall and the capacity to persist at low levels of metabolic activity through summer drought are discussed in relation to the success of this introduced species in this habitat.  相似文献   

9.
Soybean [Glycine max (L.) Merr. cv. Williams 82 and A3127] plants were grown in the field under long-term soil moisture deficit and irrigation to determine the effects of severe drought stress on the photosynthetic capacity of soybean leaves. Afternoon leaf water potentials, stomatal conductances, intercellular CO2 concentrations and CO2-assimilation rates for the two soil moisture treatments were compared during the pod elongation and seed enlargement stages of crop development. Leaf CO2-assimilation rates were measured with either ambient (340 l CO2 l–1) or CO2-enriched (1800 l CO2 l–1) air. Although seed yield and leaf area per plant were decreased an average of 48 and 31%, respectively, as a result of drought stress, leaf water potentials were reduced only an average of 0.27 MPa during the sampling period. Afternoon leaf CO2-assimilation rates measured with ambient air were decreased an average of 56 and 49% by soil moisture deficit for Williams 82 and A3127, respectively. The reductions in leaf photosynthesis of both cultivars were associated with similar decreases in leaf stomatal conductance and with small increases in leaf intercellular CO2 concentration. When the CO2-enriched air was used, similar afternoon leaf CO2-assimilation rates were found between the soil moisture treatments at each stage of crop development. These results suggest that photosynthetic capacity of soybean leaves is not reduced by severe soil moisture deficit when a stress develops gradually under field conditions.Abbreviations Ci intercellular CO2 concentrations - Aa rates of CO2 assimilation measured with ambient air - Ae rates of CO2 assimilation measured with CO2-enriched air - gs stomatal conductances - RuBPCase ribulose-1,5-bisphosphate carboxylase  相似文献   

10.
Günter Döhler 《Planta》1976,131(2):129-133
Summary CO2 exchange, 14CO2 fixation and 14C-labelled photosynthetic products of differently pigmented Anacystis nidulans (strain L 1402-1) were studied during the induction period at +30°C. The algae were grown at +35° C in an atmosphere of 0.04 vol.-% CO2 and measured under the same low CO2 concentrations. Changing the culture conditions caused alterations in the pigment composition. Under normal illumination (white light; 0.6×103 erg/ cm2 s) the relation between amounts of chlorophyll a and phycocyanin was 1:7 to 1:10. In a high light intensity (30.8×103 erg/cm2 s) the phycocyanin content was reduced (1:5 to 1:2). When the cells were grown in red light of high intensity (20×103 erg/ cm2 s) phycocyanin synthesis increased; the pigment ratio varied between 1:20 and 1:33. Anacystis cells grown under strong white light were filamentous.Photosynthetic CO2 uptake, measured with an infrared gas analyzer, was very low in algae grown in high light intensity. The pattern of 14C-labelled photosynthetic products of these algae was very similar to those of the Calvin cycle. In Anacystis cells grown under low intensities of white light or in red light 14CO2 was, at the beginning of the light period, incorporated mainly into aspatate and glycerine/serine. The enzyme activities of NAD+-specific malate dehydrogenase, ribulose-1,5-diphosphate carboxylase, aspartate and alanine aminotransferase decreased with increasing phycocyanin content. NADP+-specific malic enzyme activities showed practically no change. In contrast, phosphoenolpyruvate carboxylase activity increased with a higher rate of phycocyanin synthesis. In another series of experiments the behaviour of the PEP carboxylase activity after breakdown of the Anacystis cells was tested in differently pigmented cultures. In all cases the enzyme activities very rapidly decreased within two hours. The results obtained are discussed with reference to the correlation of pigment composition and CO2 fixation of the phosphoenolpyruvate system.
Abkürzungen Asp Aspartat - Gly/Ser Glycin/Serin - PGS 3-Phosphoglycerat - ZmP Zuckermonophosphat Herrn Professor Dr. Andre Pirson in Verehrung gewidmet  相似文献   

11.
A. Yokota  S. Kitaoka 《Planta》1987,170(2):181-189
The rate of glycolate excretion in Euglena gracilis Z and some microalgae grown at the atmospheric level of CO2 was determined using amino-oxyacetate (AOA). The extracellular O2 concentration was kept at 240 M by bubbling the incubation medium with air. Glycolate, the main excretion product, was excreted by Euglena at 6 mol·h-1·(mg chlorophyll (Chl))-1. Excretion depended on the presence of AOA, and was saturated at 1 mM AOA. A substituted oxime formed from glyoxylate and AOA was also excreted. Bicarbonate added at 0.1 mM did not prevent the excretion of glycolate. The excretion of glycolate increased with higher O2 concentrations in the medium, and was competitively inhibited by much higher concentrations of bicarbonate. Aminooxyacetate also caused excretion of glycolate from the green algae, Chlorella pyrenoidosa, Scenedesmus obliquus and Chlamydomonas reinhardtii grown on air, at the rates of 2–7 mol·h-1·(mg Chl)-1 in the presence of 0.2–0.6 mM dissolved inorganic carbon, but the cyanobacterium, Anacystis nidulans, grown in the same way did not excrete glycolate. The efficiency of the CO2-concentrating mechanism to suppress glycolate formation is discussed on the basis of the magnitude of glycolate formation in these low-CO2-grown cells.Abbreviations AOA aminooxyacetate - Chl chlorophyll - DIC dissolved inorganic carbon - HPLC high-pressure liquid chromatography - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase This is the 16th paper in a series on the metabolism of glycolate in Euglena gracilis. The 15th paper is Yokota et al. (1985c)  相似文献   

12.
The development of soybean leaves grown at fluctuating photon flux density between 100 and 1500M m-2s-1 with a period of 160 sec were compared to leaves developed under continuous light with the same mean photon flux density. Number of epidermal cells and stomata, leaf area and specific leaf weight were not affected by the periodic fluctuation of photon flux density. Chloroplastic pigment concentration and chlorophyll fluorescence reveal some photoinhibitory effects of the high photon flux density phase. Stomatal and internal CO2 conductance and the quantum yield were not affected by the light regime. In contrast ribulose 1.5 bisphosphate carboxylase/oxygenase activity before in vitro activation by CO2 and Mg++ was stimulated by the periodic illumination whereas the total amount of the enzyme and the internal leaf CO2 conductance remained steady. In conclusion, there was no major difference between leaves of plant grown either under a steady or under a periodic fluctuation of the photon flux density except some photoinhibitory symptoms under fluctuating illumination, and a higher in vivo level of activation of the Rubisco.  相似文献   

13.
The photosynthetic CO2-fixation rates, chlorophyll content, chloroplast ultrastructure and other leaf characteristics (e.g. variable fluorescence, stomata density, soluble carbohydrate content) were studied in a comparative way in sun and shade leaves of beech (Fagus sylvatica) and in high-light and low-light seedlings.
  1. Sun leaves of the beech possess a smaller leaf area, higher dry weight, lower water content, higher stomata density, higher chlorophyll a/b ratios and are thicker than the shade leaves. Sun leaves on the average contain more chlorophyll in a leaf area unit; the shade leaf exhibits more chlorophyll on a dry weight basis. Sun leaves show higher rates for dark respiration and a higher light saturation of photosynthetic CO2-fixation. Above 2000 lux they are more efficient in photosynthetic quantum conversion than the shade leaves.
  2. The development of HL-radish plants proceeds much faster than that of LL-plants. The cotyledons of HL-plants show a higher dry weight, lower water content, a higher ratio of chlorophyll a/b and a higher gross photosynthesis rate than the cotyledons of the LL-plants, which possess a higher chlorophyll content per dry weight basis. The large area of the HL-cotyledon on the one hand, as well as the higher stomata density and the higher respiration rate in the LL-cotyledon on the other hand, are not in agreement with the characteristics of sun and shade leaves respectively.
  3. The development, growth and wilting of wheat leaves and the appearance of the following leaves (leaf succession) is much faster at high quanta fluence rates than in weak light. The chlorophyll content is higher in the HL-leaf per unit leaf area and in the LL-leaf per g dry weight. There are no differences in the stomata density and leaf area between the HL- and LL-leaf. There are fewer differences between HL- and LL-leaves than in beech or radish leaves.
  4. The chloroplast ultrastructure of shade-type chloroplasts (shade leaves, LL-leaves) is not only characterized by a much higher number of thylakoids per granum and a higher stacking degree of thylakoids, but also by broader grana than in sun-type chloroplasts (sun leaves, HL-leaves). The chloroplasts of sun leaves and of HL-leaves exhibit large starch grains.
  5. Shade leaves and LL-leaves exhibit a higher maximum chlorophyll fluorescence and it takes more time for the fluorescence to decline to the steady state than in sun and HL-leaves. The variable fluorescence VF (ratio of fluorescence decrease to steady state fluorescence) is always higher in the sun and HL-leaf of the same physiological stage (maximum chlorophyll content of the leaf) than in the shade and LL-leaf. The fluorescence emission spectra of sun and HL-leaves show a higher proportion of chlorophyli fluorescence in the second emission maximum F2 than shade and LL-leaves.
  6. The level of soluble carbohydrates (reducing sugars) is significantly higher in sun and HL-leaves than in shade and LL-leaves and even reflects changes in the amounts of the daily incident light.
  7. Some but not all characteristics of mature sun and shade leaves are found in HL- and LL-leaves of seedlings. Leaf thickness, dry weight, chlorophyll content, soluble carbohydrate level, photosynthetic CO2-fixation, height and width of grana stacks and starch content, are good parameters to describe the differences between LL- and HL-leaves; with some reservations concerning age and physiological stage of leaf, a/b ratios, chlorophyll content per leaf area unit and the variable fluorescence are also suitable.
  相似文献   

14.
Perennial legume such as alfalfa have the capacity to sustain shoot regrowth and some nodule N2-fixation after removal (cutting) of shoots which contain practically all of the plant's photosynthetic capacity. The role of the roots in supporting these processes has not been fully described. Measurements were made of the nodules' responses to removal of shoots from 8-week-old seedlings in terms of N2-fixation, as nitrogenase activity (NA) measured as acetylene reduction, dark CO2 fixation, measured as in vitro phosphoenolpyruvate carboxylase (PEPC) activity, and total non-structural carbohydrate (NSC) content. These properties decreased and recovered in that sequence, which suggests that nodule NSC supported the substrate requirements of NA and PEPC immediately after cutting. The utilization and redistribution or root carbon and nitrogen, prelabeled with 14C and 15N, were also followed after cutting 8-week-old alfalfa seedlings. In the first 2 weeks of regrowth 12% of root C and 25% of root N were transferred for incorporation into new shoots. Up to 40% of the root C was used for plant respiration to support 28 days of shoot regrowth and N2-fixation. The decline of N2-fixation was slower after cutting and its minimum activity rose up 45% of pre-cut activity as root reserves were built up with plant age. Therefore, the stored reserves of nodulated roots play an important role in support of N2-fixation after cutting.Contribution No. 1265 from Plant Research Center.Contribution No. 1265 from Plant Research Center.  相似文献   

15.
After a 5-second exposure of illuminated bermudagrass (Cynodon dactylon L. var. `Coastal') leaves to 14CO2, 84% of the incorporated 14C was recovered as aspartate and malate. After transfer from 14CO2-air to 12CO2-air under continuous illumination, total radioactivity decreased in aspartate, increased in 3-phosphoglyceric acid and alanine, and remained relatively constant in malate. Carbon atom 1 of alanine was labeled predominantly, which was interpreted to indicate that alanine was derived from 3-phosphoglyceric acid. The activity of phosphoenolpyruvate carboxylase, alkaline pyrophosphatase, adenylate kinase, pyruvate-phosphate dikinase, and malic enzyme in bermudagrass leaf extracts was distinctly higher than those in fescue (Festuca arundinacea Schreb.), a reductive pentose phosphate cycle plant. Assays of malic enzyme activity indicated that the decarboxylation of malate was favored. Both malic enzyme and NADP+-specific malic dehydrogenase activity were low in bermudagrass compared to sugarcane (Saccharum officinarum L.). The activities of NAD+-specific malic dehydrogenase and acidic pyrophosphatase in leaf extracts were similar among the plant species examined, irrespective of the predominant cycle of photosynthesis. Ribulose-1, 5-diphosphate carboxylase in C4-dicarboxylic acid cycle plant leaf extracts was about 60%, on a chlorophyll basis, of that in reductive pentose phosphate cycle plants.  相似文献   

16.
A malate dehydrogenase (MDH) was characterized from the cyanobacterium Coccochloris peniocystis. The enzyme was purified approximately 180-fold and had a molecular weight of about 90000. The enzyme had a pH optimum of pH 6.7 to 7.5; a Km (malate) of 5.6 mM and Kms for NAD and NADP of 24 M and 178 M, respectively, although similar Vmax were obtained with either pyridine nucleotide. Enzyme activity was inhibited by ATP, citrate, oxalacetate, acetyl CoA and CoA. Enzyme assays with uniformly 14C-labelled malate caused no 14CO2 release, indicating this MDH is not a malic enzyme. Electrophoresis and S-200 gel filtration of the partially purified enzyme indicated a single MDH was present in this preparation. A second, less abundant, MDH was present in crude extracts. The presence of MDH in this organism is consistent with the operation of a glyoxylate cycle which, in the absence of a TCA cycle, would provide organic acids required in secondary carbon metabolism. ATP inhibition of MDH may allow for light regulation of MDH activity since, in the light, oxaloacetic acid is generated by phosphoenolpyruvate carboxylase activity.Abbreviations MDH malate dehydrogenase - PEPcase phosphoenolpyruvate carboxylase - MOPS 3-[N-Morpholino] propane sulfonic acid - TRIS Tris(hydroxymethyl)-aminomethane - EDTA Disodium Ethylenadiamine Tetraacetate - MES 2[N-Morpholino]-ethane Sulfonic Acid - EPPS N-2-Hydroxyethylpiperazine Propane - MW Molecular weight - OAA Oxaloacetic acid  相似文献   

17.
Plasma membrane vesicles, purified by aqueous two-phase partitioning, were used to investigate the presence of sugar and amino acid carriers in cotyledons and roots of Ricinus communis L. and in roots of red beet (Beta vulgaris L.). Artificial pH and electrical gradients were generated across the plasma membrane, and [14C]acetate and [14C]tetraphenylphosphonium were used to demonstrate the presence of an internal alkaline pH gradient and an internal negative membrane potential, respectively. In Ricinus cotyledons, uptake of sucrose was more strongly inhibited than that of glutamine by p-chloromercuribenzenesulphonic acid, phlorizin and phenylglyoxal. The sucrose transport system showed a high degree of substrate specificity with only the presence of maltose and phenyl--glucoside significantly affecting sucrose uptake; in contrast, the glutamine transport system was inhibited by a number of other amino acids. pH+gD-driven glutamine uptake showed saturation kinetics with a K m of 0.35 mol · m–3. Sucrose and glutamine -driven uptake was pH dependent with an optimum in the acidic range (pH 6.25) and a decrease at higher pH values. Vesicles obtained from cotyledons and roots of Ricinus showed different transport properties. In the cotyledons, gDH+gD-driven transport for both sucrose and glutamine were observed at similar levels; however, in the root tissue, pH--driven glutamine transport was the dominant uptake process. Uptake rates for glucose and fructose were low in the cotyledons whereas, in the roots, glucose and sucrose transport were slightly higher than that of fructose. In vesicles from red beet tissue there was a different uptake profile, with evidence of proton-coupled cotransport systems for sucrose and glucose, but lower uptake of glutamine and fructose. The results are discussed in relation to the reported different pathways for loading and unloading of solutes in these tissues.Abbreviations CCCP carbonyl cyanide-m-chlorophyenyl hydrazone - DEPC diethyl pyrocarbonate - NEM N-ethylmaleimide - PCMBS p-chloromercuribenzenesulfonic acid - TPP tetraphenylphosphonium ion - gDH+ proton electrochemical potential gradient - membrane potential We would like to thank the SERC(UK) and the Royal Society for financial support.  相似文献   

18.
Günter Döhler 《Planta》1974,117(1):97-99
Summary The blue-green alga Anacystis nidulans (strain L 1402-1) was grown in air (0.03 vol. % CO2) and in 3.0 vol. % CO2 at +35° C. Levels of carbonic anhydrase were 3-fold higher in air-grown cells than in CO2-grown algae. CO2 content during growth has no effect on activity of RuDP carboxylase. Activities of PEP carboxylase, malic enzyme and catalase were higher in CO2-grown Anacystis cells. In air-grown cells higher activities of malate dehydrogenase, glycolate dehydrogenase, serine-pyruvate aminotransferase and aspartate--ketoglutarate aminotransferase were found. Levels of these enzymes are relatively low compared to those in green algae and higher plants.  相似文献   

19.
Single leaf photosynthetic characteristics of Alnus glutinosa, A. incana, A. rubra, Elaeagnus angustifolia, and E. umbellata seedlings conditioned to ambient sunlight in a glasshouse were assessed. Light saturation occurred between 930 and 1400 mol m-2s-1 PAR for all species. Maximum rates of net photosynthesis (Pn) measured at 25°C ranged from 12.8 to 17.3 mol CO2m-2s-1 and rates of dark respiration ranged from 0.74 to 0.95 mol CO2m-2s-1. These values of leaf photosynthetic variables are typical of early to midsuccessional species. The rate of Pn measured at optimal temperature (20°C) and 530mol m-2s-1 PAR was significantly (p<0.01) correlated with leaf nitrogen concentration (r=0.69) and negatively correlated with the mean area of a leaf (r=–0.64). We suggest that the high leaf nitrogen concentration and rate of Pn observed for Elaeagnus umbellata and to a lesser degree for E. angustifolia are genetic adaptations related to their crown architecture.Abbreviations Pn net photosynthesis  相似文献   

20.
A heterotrophic cotton (Gossypium hirsutum L. cv. Stoneville 825) cell suspension culture was adapted to grow photoautotrophically. After two years in continuous photoautotrophic culture at 5% CO2 (balance air), the maximum growth rate of the photoautotrophic cell line was a 400% fresh weight increase in eight days. The Chl concentration was approximately 500 g per g fresh weight.Elevated CO2 (1%–5%) was required for culture growth, while the ambient air of the culture room (600 to 700 ul CO2 1–1) or darkness were lethal. The cell line had no net photosynthesis at 350 ul 1–1 CO2, 2% O2, and dark respiration ranged from 29 to 44 mol CO2 mg–1 Chl h–1. Photosynthesis was inhibited by O2. The approximate 1:1 ratio of ribulose 1,5-bisphosphate carboxylase (RuBPcase) to phosphoenolpyruvate carboxylase (PEPcase) (normally about 6:1 in mature leaves of C3 plants) was due to low RuBPcase activity relative to that of C3 leaves, not to high PEPcase activity. The PEPcase activity per unit Chl in the cell line was identical to that of spinach leaves, while the RuBPcase activity was only 15% of the spinach leaf RuBPcase activity. RuBPcase activity in the photoautotrophic cells was not limited by a lack of activation in vivo, since the enzyme in a rapidly prepared cell extract was 73% activated. No evidence of enzyme inactivation by secondary compounds in the cells was found as can be found with cotton leaves. Low RuBPcase activity and high respiration rates are most likely important factors in the low photosynthetic efficiency of the cells at ambient CO2.Abbreviations Chl chlorophyll - COT heterotrophic cotton cell line - COT-P photoautotrophic cotton cell line - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose 1,5-bisphosphate - RuBPcase RuBP carboxylase - PEP phosphoenolpyruvate - PEPcase phosphoenolpyruvate carboxylase - MX Murashige and Skoog medium with 0.4 mg 1–1 2,4-D - KT photomixotrophic medium with 1% sucrose - KTo KT medium with no carbohydrate - KTPo KTo medium supplemented with 0.3 M Picloram - CER CO2 exchange rate - PCER CO2 exchange rate in the light  相似文献   

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