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1.
Dactylis glomerata accumulated fructosan more rapidly at 5° than at 15—20°. The pattern of incorporation of 14CO2 into fructosan was determined in plants grown at 5°. During the major period of fructosan synthesis there was initial incorporation of label into mono- and disaccharides, and progressive synthesis of polymeric material occurred subsequently. Rates and levels of synthesis were much lower in leaf blades than in leaf bases. The MW distribution of the polymeric material in leaf bases differed from that in the blades and from that observed in plants which synthesize inulin. 相似文献
2.
A 10-fold purification of sucrose sucrose fructosyl transferase from Cichorium intybus roots was achieved by ammonium sulphate fractionation and DEAE-cellulose column chromatography. The energy of activation for this enzyme was ca 48 kJ/mol sucrose. Sucrose sucrose fructosyl transferase and invertase were prominent during early months of growth. Evidence obtained from: (1) the changes in carbohydrate composition at monthly intervals; (2) comparative studies on fructosyl transferase and invertase at different stages of root growth; and (3) incubation studies with [14C]glucose, [14C]fructose and [14C]sucrose revealed that, during the later stages of root growth, fructosan hydrolase is responsible for fructosan hydrolysis. No evidence for the direct transfer of fructose from sucrose to high Mr glucofructosans was obtained. 相似文献
3.
《Phytochemistry》1986,25(12):2765-2768
Incorporation of [14C]sucrose into difructosyl glucose (F2G), trifructosyl glucose (F3G) and tetrafructosyl glucose (F4G) in the presence of various nucleoside triphosphates revealed that formation of F4G and F3G is retarded in the presence of ATP, and formation of F3G and F2G is significantly enhanced in the presence of CTP, whereas UTP has no effect on the synthesis of these oligosaccharides. Different fructosyl transferases seem to be responsible for the different fructosylation steps and self transfer seems to be the major pathway for fructosan synthesis. Utilization of added glucose, which is formed by sucrose sucrose fructosyl transferase action in vivo, is completely inhibited in acetate buffer whereas in phosphate, citrate and citrate-phosphate buffers glucose is actively utilized. In the presence of fluoride ions both glucose utilization and its conversion to CO2 is inhibited by ca 50%. CO2 production from [14C]glucose is completely inhibited in acetate ions. No evidence for the incorporation of 14C from [14C]glucose into [14C]sucrose is observed. The ratio of bound fructose to bound glucose is the same in the entire length of the root indicating that there is no preferential zone for fructosan synthesis. 相似文献
4.
The possible role of fructosyl transferase in the biosynthesis of fructosans in Agave americana was investigated. This enzyme was extracted from A. americana stem and purified 17.5-fold by salt fractionation and DEAE-cellulose chromatography. The optimum conditions for the enzyme were pH 6. 1, temperature 37°, substrate concentration 20% and Km 3.6 × 10?1 M; Ag+, Pb 2+, Hg2+, Al3+, Sn2+, CN? acted as inhibitors and Ca2+, Mg2+, Co2+ and Li+ actemd as activators. Only sugars of the type F ~ R (R-aidose), e.g. sucrose and raffinose acted as substrates for the enzyme. The donor acceptor specificity of the enzyme was studied extensively. Sugars sucrose. None of the intermediates of fructosan biosynthesis from sucrpse acted as fructose donors. The possible acceptors from sucrose and raffinose. The enzyme was capable of building up oligosaccharides up to FIOG from sucrose. None of the intermediates of fructosan biosynthesis from sucrose acted as fructose donors. The possible mechanism of fructosan biosynthesis from sucrose is discussed. 相似文献
5.
Carbon-14 Distribution in Carbohydrates of Immature Zea mays. Kernels Following CO(2) Treatment of Intact Plants
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Shannon JC 《Plant physiology》1968,43(8):1215-1220
Shortly after Zea mays L. plants were exposed to 14CO2, most of the radioactivity in the kernel occurred in the free monosaccharides, glucose and fructose. Later the proportion of 14C in sucrose increased and that in the monosaccharides declined. These data have been interpreted as showing that the translocated sugar is hydrolyzed prior to or during its movement into the storage cells of the endosperm. This hydrolysis appears to occur in the “pedicel region” of the kernel. After entry into the endosperm tissue, sucrose was rapidly resynthesized from the monosaccharides prior to its utilization in starch synthesis. 相似文献
6.
Previous work showed that the segl mutant of barley (Hordeum vulgare cv Betzes) did not differ from normal Betzes in plant growth, photosynthesis, or fertility, but it produced only shrunken seeds regardless of pollen source. To determine whether defects in sucrose uptake or starch synthesis resulted in the shrunken condition, developing grains of Betzes and segl were cultured in [14C]sucrose solutions after slicing transversely to expose the endosperm cavity and free space. In both young grains (before genotypes differed in dry weight) and older grains (17 days after anthesis, when segl grains were smaller than Betzes), sucrose uptake and starch synthesis were similar in both genotypes on a dry weight basis. To determine if sucrose was hydrolyzed during uptake, spikes of Betzes and segl were allowed to take up [fructose-U-14C]sucrose 14 days after anthesis and the radioactivity of endosperm sugars was examined during 3 hours of incubation. Whereas less total radioactivity entered the endosperm and the endosperm cavity (free space) of segl, in both genotypes over 96% of the label of endosperm sugars was in sucrose, and there was no apparent initial or progressive randomization of label among hexose moieties of sucrose as compared to the free space sampled after 1 hour of incubation. We conclude that segl endosperms are capable of normal sucrose uptake and starch synthesis and that hydrolysis of sucrose is not required for uptake in either genotype. Evidence suggests abnormal development of grain tissue of maternal origin during growth of segl grains. 相似文献
7.
The labeling pattern of the sugar moieties of 1-kestose after in vivo pulse labeling with 14CO2 was not the same as that after in vitro labeling with 14C-sucrose. The two fructosyl residues of 1-kestose had similar specific radioactivities after in vitro synthesis, but after in vivo radiolabeling the specific radioactivity of the terminal fructosyl moiety was significantly less than the internal fructosyl moiety. Evidence is presented that the uneven specific radioactivity of in vivo radiolabeling results from enzymatic transfer of terminal fructosyl residue from 1-kestose to sucrose. 相似文献
8.
The effects of kinetin on starch and sugar levels and on 14CO2 and 32P-orthophosphate labeling patterns of floated Chinese cabbage (Brassica pekinensis) leaf discs were investigated. Kinetin caused gross starch degradation. Neutral sugars were depressed by 30 to 40% in leaf tissue treated with kinetin for 24 hours. 14CO2 labeling of leaf discs pretreated with kinetin for 24 hours showed increased radioactivity in chloroform-soluble material and most sugar phosphates, and a 35 to 40% decrease in radioactivity in the neutral sugars, glucose, sucrose, and fructose. Incorporation into ATP was increased by 40% by kinetin. 32P-Orthophosphate uptake was inhibited 30% by kinetin. When corrected for uptake, kinetin stimulated incorporation into chloroform-soluble material but had little effect on other cell fractions. These results indicate that kinetin mobilizes starch reserves and increases the flow of sugars required for the synthesis of lipids and structural materials in floated discs. 相似文献
9.
Sugar Transport in Immature Internodal Tissue of Sugarcane: II. Mechanism of Sucrose Transport
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Bowen JE 《Plant physiology》1972,49(5):789-793
The mechanism by which sucrose is transported into the inner spaces of immature internodal parenchyma tissue of sugarcane (Saccharum officinarum L. var. H 49-5) was studied in short term experiments (15 to 300 seconds). Transport of sucrose, glucose, and fructose was each characterized by a Vmax of 1.3 μmoles/gram fresh weight·2 hours, and each of these three sugars mutually and competitively inhibited transport of the other two. When 14C-glucose was supplied exogenously, 14C-glucose 6-phosphate and 14C-glucose were the first labeled compounds to appear in the tissue; no 14C-sucrose was detected until after 60-second incubation. After 15-second incubation in 14C-sucrose, all intracellular radioactivity was in glucose, fructose, glucose 6-phosphate, and fructose 6-phosphate; trace amounts of 14C-sucrose were found after 30 seconds and after 5 minutes, 71% of the intracellular radioactivity was in sucrose. Although it was possible that sucrose was transported intact into the inner space and then immediately hydrolyzed, it was shown that the rate of hydrolysis under these conditions was too low to account for the rate of hexose accumulation. Pretreatment of the tissue with rabbit anti-invertase antiserum eliminated sucrose transport, but had no effect on glucose transport. Since the antibodies did not penetrate the plasmalemma, it was concluded that sucrose was hydrolyzed by an invertase in the free space prior to transport. The glucose and fructose moieties, or their phosphorylated derivatives, were then transported into the inner space and sucrose was resynthesized. No evidence for the involvement of sucrose phosphate in transport was found in these experiments. 相似文献
10.
Measurement of protein synthesis in rat lungs perfused in situ 总被引:6,自引:6,他引:0
Compartmentalization of amino acid was investigated to define conditions required for accurate measurements of rates of protein synthesis in rat lungs perfused in situ. Lungs were perfused with Krebs–Henseleit bicarbonate buffer containing 4.5% (w/v) bovine serum albumin, 5.6mm-glucose, normal plasma concentrations of 19 amino acids, and 8.6–690μm-[U-14C]phenylalanine. The perfusate was equilibrated with the same humidified gas mixture used to ventilate the lungs [O2/CO2 (19:1) or O2/N2/CO2 (4:15:1)]. [U-14C]Phenylalanine was shown to be a suitable precursor for studies of protein synthesis in perfused lungs: it entered the tissue rapidly (t½, 81s) and was not converted to other compounds. As perfusate phenylalanine was decreased below 5 times the normal plasma concentration, the specific radioactivity of the pool of phenylalanine serving as precursor for protein synthesis, and thus [14C]phenylalanine incorporation into protein, declined. In contrast, incorporation of [14C]histidine into lung protein was unaffected. At low perfusate phenylalanine concentrations, rates of protein synthesis that were based on the specific radioactivity of phenylalanyl-tRNA were between rates calculated from the specific radioactivity of phenylalanine in the extracellular or intracellular pools. Rates based on the specific radioactivities of these three pools of phenylalanine were the same when extracellular phenylalanine was increased. These observations suggested that: (1) phenylalanine was compartmentalized in lung tissue; (2) neither the extracellular nor the total intracellular pool of phenylalanine served as the sole source of precursor for protein; (3) at low extracellular phenylalanine concentrations, rates of protein synthesis were in error if calculated from the specific radioactivity of the free amino acid; (4) at high extracellular phenylalanine concentrations, the effects of compartmentalization were negligible and protein synthesis could be calculated accurately from the specific radioactivity of the free or tRNA-bound phenylalanine pool. 相似文献
11.
Relationship between Photosynthesis and Protein Synthesis in Maize: I. Kinetics of Translocation of the Photoassimilated Carbon from the Ear Leaf to the Seed 总被引:2,自引:2,他引:0
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To gain a better understanding of the biochemical basis for partitioning of photosynthetically fixed carbon between leaf and grain, a 14CO2 labeling study was conducted with field-grown maize plants 4 weeks after flowering. The carbon flow was monitored by separation and identification of 14C assimilates and 14C storage components within each tissue during the chase period (from 4 to 96 hours) following a 5 minute 14CO2 pulse. In the labeled ear leaf, the radioactivity strongly decreased to reach, at the end of the experiment, about 12% of the total incorporated radioactivity, mostly associated with sucrose and proteins. Nevertheless, an unexpected reincorporation of radioactivity was observed either in leaf starch or proteins, the day following the pulse. Conversely, the radioactivity in the grain increased to attain 66% of the total incorporated 14C after a 96 hour chase. The photosynthates, mostly sucrose, organic and free amino acids, rapidly translocated towards the developing seeds, served as precursors for the synthesis of seed storage compounds, starch, and proteins. They accumulate in free form for 24 hours before being incorporated within polymerized storage components. This delay is interpreted as a necessary prerequisite for interconversions prior to the polycondensations. In the grain, the labeling of the storage molecules, either in starch or in storage protein groups (salt-soluble proteins, zein, and glutelin subgroups), was independent of their chemical nature but dependent on their pool size. 相似文献
12.
This study was designed to compare the uptake and distribution of 14C among fructose, glucose, sucrose, and starch in the cob, pedicel, and endosperm tissues of maize (Zea mays L.) kernels induced to abort by high temperature with those that develop normally. Kernels cultured in vitro at 30 and 35°C were transferred to [14C]sucrose media 10 days after pollination. Kernels cultured at 35°C aborted prior to the onset of linear dry matter accumulation. Significant uptake into the cob, pedicel, and endosperm of radioactivity associated with the soluble and starch fractions of the tissues was detected after 24 hours in culture on labeled media. After 8 days in culture on [14C]sucrose media, 48 and 40% of the radioactivity associated with the cob carbohydrates was found in the reducing sugars at 30 and 35°C, respectively. This indicates that some of the sucrose taken up by the cob tissue was cleaved to fructose and glucose in the cob. Of the total carbohydrates, a higher percentage of label was associated with sucrose and a lower percentage with fructose and glucose in pedicel tissue of kernels cultured at 35°C compared to kernels cultured at 30°C. These results indicate that sucrose was not cleaved to fructose and glucose as rapidly during the unloading process in the pedicel of kernels induced to abort by high temperature. Kernels cultured at 35°C had a much lower proportion of label associated with endosperm starch (29%) than did kernels cultured at 30°C (89%). Kernels cultured at 35°C had a correspondingly higher proportion of 14C in endosperm fructose, glucose, and sucrose. These results indicate that starch synthesis in the endosperm is strongly inhibited in kernels induced to abort by high temperature even though there is an adequate supply of sugar. 相似文献
13.
Manfred Kluge 《Planta》1969,88(2):113-129
Summary Detached phyllodia ofBryophyllum tubiflorum were fed under illumination with14CO2 at different times during the light/dark period (12:12 hours). After photosynthesis in presence of14CO2 during the intrinsic dark period the greatest part of soluble radioactivity was found in malate. When the same experiment was repeated during the light period, radioactivity was incorporated mainly into sucrose in the first hours while malate was labelled rather weakly. In the late afternoon (last third of the light period), malate became most heavily labelled again during photosynthesis with14CO2.Our results indicate that the synthesis of malate by PEP-carboxylase/malate dehydrogenase is inhibited at certain times during the night/day period by end product inhibition of PEP-carboxylase, as was demonstrated byQueiroz (1967, 1968) andTing (1968) in vitro.During inhibition of the PEP-carboxylase there is no competition between the synthesis of malate and CO2-fixation by the Calvin cycle. Thus radioactivity can flow into sucrose via the Calvin cycle during this time. When the malate content of the phyllodia is low, CO2-fixation by PEP-carboxylase is not inhibited. Now this pathway dominates over photosynthesis via the Calvin cycle, for PEP-carboxylase has a higher affinity for CO2 than carboxydismutase. Therefore malate now becomes more labelled than sucrose. 相似文献
14.
A comparative study was made of the ability of cultured pith tissue, leaves of buds induced from callus, and mature leaf tissue of Nicotiana tabacum L. ‘Maryland Mammoth’ to fix carbon, as determined by light-induced C14O2 incorporation. Photosynthetic ability was then correlated with the fine structure of chloroplasts from these tissues. The light to dark incorporation ratio for C14O2 was at least 3 times as great in the leaf tissue as in growing cultured tissue. The chlorophyll content of the leaf tissue was 10 times as great. The carbon fixation pattern of all the tissues, as determined by radioautographs of chromatogramed extracts, was qualitatively the same. The rate of sucrose synthesis differed greatly, since 20% of the total radioactivity of the extracts from mature leaf tissue appeared in sucrose, while only 1.0% was found in sucrose from callus extracts. The incorporation of C14O2 into sugars was inhibited in all the tissue by DCMU (3,4-dichlorophenyl,1, 1-dimethylurea). Cultured tissue past the log phase of growth was intermediate between the younger cultured tissue and the leaf tissue in its chlorophyll content and ability to incorporate C14O2 in the light. Proplastids from dark-grown callus possessed stroma lamellae, but prolamellar bodies were not observed. The chloroplasts from growing callus were partially differentiated in comparison with chloroplasts from mature leaf tissue, since each granum had only 4-7 lamellae. Chloroplasts from callus past the log phase of growth were indistinguishable from those in mature leaves. This study establishes that the differentiation of chloroplasts in cultured tissue is a function of the growth rate of the tissue. The growth rate and degree of differentiation of the tissue can be regulated, so a well-defined system is available for the experimental study of chloroplast differentiation. 相似文献
15.
The kinetic behavior of translocation profiles indicates that their shape is determined largely by the rate at which tracer enters the sieve tubes in the source leaf. Confirmation of this relationship was sought by investigating the kinetics of 14C in the immediate source pool for translocated sucrose in soybean (Glycine max L., cv. Bragg) and morning glory (Ipomea nil Roth, cv. Scarlet O'Hara) leaves. Quantitative microautoradiography was used to follow the water-soluble 14C contents of the companion cells in minor veins after pulse-labeling with 14CO2. In both morning glory and soybean, the observed kinetics in the companion cells matched reasonably well those expected from the shape of the translocation profiles.
Marked compartmentation of sucrose was evident in soybean leaves in that the specific radioactivity of total leaf sucrose was greatest immediately after labeling and quickly declined, whereas labeling in the companion cells was low at first and did not reach a maximum for about 35 minutes. In morning glory leaves, the kinetics of sucrose specific radioactivity and of companion cell-labeling more closely paralleled one another.
相似文献16.
Illuminated flag leaves of Triticum monococcum(2X), T. urartu(2X), T. dicoccum(4X), T. dicoccoides(4X), and T. aestivum(6X) were exposed to 14CO2 for 10 seconds and subsequently allowed to continue photosynthesis in the ambient air for periods of up to 2 minutes. The relative distribution of 14C among water-soluble products in the leaves was similar for each species at each sampling time. After the 10-second pulse of 14CO2, radioactivity was mainly in phosphate esters with less than 5% in C4 acids. Subsequently, radioactivity increased in sucrose, glycine, and serine at the expense of that in phosphate esters. By 2 minutes, between 18% and 29% of the 14C was in glycine plus serine. The results suggest rapid photorespiration in all species and an absence of C4 photosynthesis. 相似文献
17.
Major ethanol-soluble carbohydrate and organic acid constituents of white clover (Trifolium repens) have been identified by use of high-performance liquid chromatography and gas chromatography. In leaves, petioles, roots, and nodules, pinitol (3-O-methyl chiro-inositol) is the predominant sugar, with sucrose present in lower concentration. In leaves and petioles there are significant levels of α- and β-methyl glucosides, linamarin, glucose, and fructose. In the nodules glucose is rarely present at detectable levels. The concentration of pinitol is generally greater than 25 millimolar in each tissue examined whereas the level of sucrose varies depending on the time of day. Sucrose is the major sugar significantly labeled during 1 hour administration of 14CO2 and accounts for more than 99% of all the radioactivity detected in the nodules at early times. Between 3 and 7 hours after labeling, 6% of the radioactivity is found in the organic acids fraction and 5% in the basic fraction of nodules. Malonic acid does not appear to be present in unusually high concentrations in either leaves or nodules of white clover. 相似文献
18.
The pathway of phloem unloading and the metabolism of translocated sucrose were determined in corn (Zea mays) seedling roots. Several lines of evidence show that exogenous sucrose, unlike translocated sucrose, is hydrolyzed in the apoplast prior to uptake into the root cortical cells. These include (a) presence of cell wall invertase activity which represents 20% of the total tissue activity; (b) similarity in uptake and metabolism of [14C]sucrose and [14C]hexoses; and (c) randomization of 14C within the hexose moieties of intracellular sucrose following accumulation of [14C] (fructosyl)sucrose. Conversely, translocated sucrose does not undergo apoplastic hydrolysis during unloading. Asymmetrically labeled sucrose ([14C](fructose)sucrose), translocated from the germinating kernels to the root, remained intact indicating a symplastic pathway for unloading. In addition, isolated root protoplasts and vacuoles were used to demonstrate that soluble invertase activity (Vmax = 29 micromoles per milligram protein per hour, Km = 4 millimolar) was located mainly in the vacuole, suggesting that translocated sucrose entered via the symplasm and was hydrolyzed at the vacuole prior to metabolism. 相似文献
19.
Enhancement of [C]Sucrose Export from Source Leaves of Vicia faba by Gibberellic Acid 总被引:2,自引:0,他引:2
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The effect of gibberellic acid (GA3) on sucrose export from source leaves was studied in broad bean (Vicia faba L.) plants trimmed of all but one source and one sink leaf. GA3 (10 micromolar) applied to the source leaf, enhanced export of [14C]sucrose (generated by 14CO2 fixation) to the root and to the sink leaf. Enhanced export was observed with GA treatments as short as 35 minutes. When GA3 was applied 24 hours prior to the 14CO2 pulse, the enhancement of sucrose transport toward the root was abolished but transport toward the upper sink leaf was unchanged. The enhanced sucrose export was not due to increased photosynthetic rate or to changes in the starch/sucrose ratio within the source leaf; rather, GA3 increased the proportion of sucrose exported. After a 10-min exposure to [14C]GA3, radioactivity was found only in the source leaf. Following a 2 hour exposure to [14C]GA3, radioactivity was distributed along the entire stem and was present in both the roots and sink leaf. Extraction and partitioning of GA metabolites by thin layer chromatography indicated that there was a decline in [14C]GA3 in the lower stem and root, but not in the upper stem. This pattern of metabolism is consistent with the disappearance of the GA3 effect in the lower stem with time after treatment. We conclude that in the short term, GA3 enhances assimilate export from source leaves by increasing phloem loading. In the long term (24 hours), the effect of GA3 is outside the source leaf. GA3 accumulates in the apical region resulting in enhanced growth and thus greater sink strength. Conversely, GA3 is rapidly metabolized in the lower stem thus attenuating any GA effect. 相似文献
20.
The turnover and transport of sugars are described in peach (Prunus persica L. Batsch), a species exporting both sucrose and sorbitol. Apparent export rate was slower in peach leaves than in leaves of herbaceous species. Sorbitol was the major soluble end product of photosynthesis and the major soluble carbohydrate in the leaf (higher than sucrose). Carbon fluxes were described using 14C labeling, radioactivity loss curves, and compartmental analysis during the second half of the photoperiod when chemical steady state was reached for soluble carbohydrates. The measured specific radioactivity of sucrose was typical of a primary product. The delayed decrease in specific radioactivity of sorbitol indicated that part of it was secondarily synthesized. Sucrose is proposed to be the carbon source for the delayed synthesis of sorbitol in the light. The sorbitol to sucrose ratio was higher in the petiole than in the leaf tissues. In phloem sap, obtained using stylectomy of aphids and collected from the main stem between source leaves and apex, this ratio was lower than in the petiole, suggesting a preferential sorbitol demand by sinks. 相似文献