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1.
Biosynthesis of willardiine and isowillardiine in germinating pea seeds and seedlings 总被引:1,自引:1,他引:0
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The synthesis of the pyrimidinyl amino acids willardiine and isowillardiine was studied in vivo and in vitro. Uracil derivatives stimulate the biosynthesis of both compounds; the free base is the most effective. Significant incorporation of [2-(14)C]uracil and [6-(14)C]orotate into willardiine and isowillardiine was found. Incorporation of [6-(14)C]orotate was substantially decreased in the presence of uracil, and to a lesser extent by uridine and UMP. [3-(14)C]Serine was incorporated into the alanine side chain of the two uracilylalanines but not into the ring. The effect of a number of uracil analogues and inhibitors of pyrimidine metabolism was examined. Some were shown to stimulate the biosynthesis; the most noticeable effects were obtained with 6-azauracil and 2-thiouracil. Attempts to obtain extracts capable of synthesizing the uracilylalanines from uracil and serine were unsuccessful, but weak activity was observed when serine was replaced by O-acetylserine. 相似文献
2.
Incorporation of radioactivity from [6-14C]orotate into the pyrimidine constituents of shoots of Pisum sativum, Phaseolus vulgaris and Lathyrus tingitanus was examined with special reference to the unusual pyrimidine constituents. With each species, although 80% of the orotate supplied was catabolized to β-alanine, all the pyrimidine derivatives became radioactively labelled. With Pisum, the major part of the radioactivity incorporated into pyrimidines was located in UMP and the uracil derivatives, including the uracilyl amino acids willardiine and isowillardiine. With Phaseolus, UMP and the uracil derivatives were again the major radioactive products; incorporation of radioactivity into 5-ribosyluracil (pseudouridine), which accumulates in Phaseolus tissues, was comparable to the incorporation into orotidine and twice that found in cytidine. Lathyrus incorporated a substantially larger part of the presented [6-14C] orotate into pyrimidine derivatives than did the other two species. CMP was the most highly radioactive product, followed next by lathyrine and UMP. Surprisingly, 20% of the total radioactivity incorporated into pyrimidines by Lathyrus was located in the pyrimidine amino acid lathyrine. This confirms previous evidence that lathyrine is essentially a product of the orotate pathway. The overall recovery of radioactivity in all three species was 93–95%. The data emphasize the necessity of including the less common pyrimidine constituents, as well as the common ones, in quantitative studies of pyrimidine metabolism in plants. 相似文献
3.
The enzymic activity responsible for synthesis of willardiine and isowillardiine in pea seedlings has been extracted and partially purified. Fresh tissue, pulverized in liquid-N2, was extracted in a phosphate buffer (pH 7) and subjected to fractional precipitation with ammonium sulphate. After desalting on Sephadex G-25 and concentration by ultrafiltration, the fraction containing the activity was chromatographed sequentially on DEAE-Sepharose CL-6B, DEAE-cellulose (DE 52) and Sephadex G-200. Electrophoretic separation in polyacrylamide gels was also used. A 120-fold purification was achieved but at no stage was there any indication of a separation of willardiine synthase activity from that of isowillardiine synthase. Both activities paralleled one another when the enzymic preparation was progressively denatured by subjecting it to gradually increasing temperatures. Similarly, ageing at 4° and at ?196° resulted in a parallel loss of activity. Both synthase activities were maximal at 7.8–7.9and the pH optimum curves were of closely similar shape. From the results described, it is concluded that a single enzyme of relatively low MW (ca 50 000) is responsible for the synthesis of both uracilylalanines. Studies of the alanylation of uracil using a pyridoxal-metal ion model-enzyme system are described. 相似文献
4.
Comparative feeding experiments in CuCl2,- and UV-treated lucerne (Medicago sativa) seedlings have shown that 2′,4,4′-trihydroxychalcone-[carbonyl-14C] and formononetin-[Me-14C] but not 2′,4′-dihydroxy-4-methoxychalcone-[carbonyl- 14C] or daidzein-[4-14C] were incorporated into the phytoalexins demethylhomopterocarpin, sativan and vestitol, and also into 9-O-methylcoumestrol. The synthesis of 9-O-methylcoumestrol is greatly stimulated by this abiotic treatment but coumestrol production is not noticeably affected. Daidzein and the trihydroxychalcone were precursors of coumestrol. The results are interpreted in favour of a mechanism in which methylation is an integral part of the aryl migration process associated with the biosynthesisof 4′-methoxyisoflavonoids. Formononetin, 2′,7-dihydroxy-4′-methoxyisoflavone-[Me-14C], 7-hydroxy-4′-methoxyisoflavanone-[Me-14C] and 2′,7-dihydroxy-4′-methoxyisoflavanone-[Me-14C] were all excellent precursors of demethylhomopterocarpin, sativan, vestitol and 9-O-methylcoumestrol, and thus a metabolic grid may be involved in their biosynthetic origin. 相似文献
5.
A method is described for the chemical synthesis of stigmasta-5,24-dien-3β-ol-[26-14C] and (24S)-24-ethylcholesta-5,25-dien-3β-ol-[26-14C] (clerosterol). 28-Isofucosterol-[7-3H2] fed to developing barley seedlings (Hordeum vulgare) was incorporated into sitosterol and stigmasterol confirming the utilisation of a 24-ethylidene sterol intermediate in 24α-ethyl sterol production in this plant. Also, the use of mevalonic acid-[2-14C(4R)-4-3H1] verified the loss of the C-25 hydrogen of 28-isofucosterol during its conversion into sitosterol and stigmasterol in agreement with the previously postulated isomerisation of the 24-ethylidene sterol to a Δ24(25)-sterol prior to reduction. However, feeding stigmasta-5,24-dien-3β-ol [26-14C] to barley seedlings gave very low incorporation into sitosterol. Attempts to trap radioactivity from mevalonic-[2-14C(4R)-4-3H1] in stigmasta-5,24-dien-3β-ol when this unlabelled sterol was administered to barley seedlings gave only a very small incorporation although both 28-isofucosterol and sitosterol were labelled. 相似文献
6.
Feeding experiments have shown that 2′-7-dihydroxy-4′-methoxy-isoflavone-[Me-14C] and -isoflavanone-[Me-14C] are efficient precursors of the phytoalexins demethylhomopterocarpin, sativan and vesitol in CuCl2-treated lucerne (Medicago sativa) seedlings. Demethylhomopterocarpin-[Me-14C] was also incorporated into sativan and vestitol, and vestitol-[Me-14C] was incorporated into demethylhomopterocarpin and sativan. Thus, the pterocarpan demethylhomopterocarpin and the 2′-hydroxy-isoflavan vestitol are interconvertible in M. sativa, but incorporation data, and the results of kinetic feeding experiments with l-phenylalanine-[U-14C] suggest that these compounds are synthesized simultaneously from a common intermediate, which could be involved in the interconversion. A carbonium ion, derived from an isoflavanol, a likely intermediate in the biosynthetic reductive sequence from 2′,7-dihydroxy-4′-methoxy-isoflavone and -isoflavanone, is proposed as this common intermediate. 7-Hydroxy-2′,4′-dimethoxyisoflavone-[4′-Me-14C] was a very poor precursor of all three phytoalexins. Sativan, then, is most probably derived by methylation of vestitol. The incorporation of vestitol-[Me-14C] into demethylhomopterocarpin, but not into maackiain, pterocarpan phytoalexins of red clover (Trifolium pratense), is also demonstrated. 相似文献
7.
Transport and Metabolism of 1-Aminocyclopropane-1-carboxylic Acid in Sunflower (Helianthus annuus L.) Seedlings 总被引:1,自引:1,他引:0
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Transport and metabolism of [2,3-14C] 1-aminocyclopropane-1-carboxylic acid (ACC) from roots to shoots in 4-day-old sunflower (Helianthus annuus L.) seedlings were studied. [14C]ACC was detected in, and 14C2H4 was evolved from, shoots 0.5 hours after [14C]ACC was supplied to roots. Ethylene emanation from the shoots returned to normal levels after 6 hours. The roots showed a similar pattern, although at 24 hours ethylene emanation was still slightly higher than in those plants that did not receive ACC. [14C]N-malonyl-ACC (MACC) was detected in both tissues at all times sampled. [14C]MACC levels surpassed [14C]ACC levels in the shoot at 2 hours, whereas [14C]MACC levels in the root remained below [14C]ACC levels until 6 hours, after which they were higher. Thin-layer chromatography analysis identified [14C] ACC in 1-hour shoot extracts, and [14C]MACC was identified in root tissues at 1 and 12 hours after treatment. [14C]ACC and [14C] MACC in the xylem sap of treated seedlings were identified by thin-layer chromatography. Xylem transport of [14C]ACC in treated seedlings, and transport of ACC in untreated seedlings, was confirmed by gas chromatography-mass spectrometry. Some evidence for the presence of [14C]MACC in xylem sap in [14C]ACC-treated seedlings is presented. A substantial amount of radioactivity in both ACC and MACC fractions was detected leaking from the roots over 24 hours. A second radiolabeled volatile compound was trapped in a CO2-trapping solution but not in mercuric perchlorate. Levels of this compound were highest after the peak of ACC levels and before peak MACC levels in both tissues, suggesting that an alternate pathway of ACC metabolism was operating in this system. 相似文献
8.
Tracer feeding experiments with Camptotheca acuminata plants show that [1′-14C]L-tryptophan, [Ar-3H4]L-tryptophan, [Ar-3H4,1′-14C]tryptophan, [1′-14C]-tryptamine, [2-14C]DL-mevalonate, and [2-14C]geraniol-[2-14C]nerol are incorporated into camptothecin. Direct stem injection of the labeled precursors into C. acuminata plants resulted in a substantial increase in the activity of isolated Camptotheca alkaloids as compared to root feeding of the same tracer. 相似文献
9.
Keith G. Allen Derek V. Banthorpe Barry V. Charlwood Olusegun Ekundayo John Mann 《Phytochemistry》1976,15(1):101-107
Partial degradations of (+)-isothujone biosynthesised in Tanacetum vulgare after feeding IPP-[4-14C], DMAPP-[4-14C] or 3,3-dimethylacrylate-[Me-14C], and of geraniol and (+)-pulegone formed in Pelargonium graveolens and Mentha pulegium respectively after uptake of 3,3-dimethylacrylate-[Me-14C], indicated that none of these metabolites was a direct source of the part of the monoterpene skeleton derived hypothetically from DMAPP. Uptake of glucose-[U14C] into P. graveolens led, in contrast, to both IPP and DMAPP-derived moieties of geraniol being extensively labelled. Feeding of l-valine-[U-14C] and l-leucine-[U-14C] to all three plants resulted in negligible incorporation of tracer into monoterpenes. A soluble enzyme system prepared from foliage of T. vulgare that had been exposed to CO2-[14C] for 20 days converted isotopically-normal IPP into GPP with the DMAPP-derived portion containing essentially all (>98%) of the radioactivity present. These observations and those previously obtained from feeding experiments with other [14C]-labelled precursors on the same plant species are consistent with the occurrence of two metabolic pools of intermediates for monoterpene biosynthesis, one of which is probably protein-bonded. 相似文献
10.
The amounts of d-alanine derivatives, γ-l-glutamyl-d-alanine and N-malonyl-d-alanine, increase rapidly during the early growth of pea seeds. Pyruvate-[1?14C], l-alanine-[U?14C], d-alanine-[U?14C], l-alanine-[15N] and 15NH4Cl were therefore fed to the seedlings and the incorporation investigated. Labelling results revealed that pea seedlings can utilize these erogenous compounds to form d-alanine and that labelled l-alanine is effectively converted to the d-enantiomer with retention of 14C and, largely, 15N label. Enzyme analyses in vitro provided additional evidence that the extract of pea seedlings catalyzes the direct conversion of l-alanine to d-alanine. The data suggest that the de novo synthesis of d-alanine in pea seedlings occurs by a racemase reaction. 相似文献
11.
Paul M. Dewick 《Phytochemistry》1975,14(4):979-982
Feeding experiments with dl-phenylalanine-[1-14C] have demonstrated the de novo synthesis of the pterocarpan phytoalexins demethylhomopterocarpin and maackiain in CuCl2-treated Trifolium pratense L. seedlings. 2′,4′,4-Trihydroxychalcone-[carbonyl-14C] and 7-hydroxy-4′-methoxyisoflavone-[methyl-14C] (formononetin) were readily incorporated into demethylhomopterocarpin and maackiain, but 2′,4′-dihydroxy-4-methoxychalcone-[carbonyl-14C] and 7,4′-dihydroxyisoflavone-[T] (daidzein) proved inefficient precursors. The trihydroxychalcone was also an excellent precursor of formononetin in T. pratense, but the trihydroxymethoxychalcone and daidzen were poorly incorporated. These observations offer further evidence that methylation may be an associated part of the mechanism for aryl migration in the biosynthesis of formononetin. 相似文献
12.
We studied 14CO2 evolution from ring-labeled [2,6-14C]parathion (O,O-diethyl-O-p-nitrophenyl phosphorothioate) in the rhizosphere of rice seedlings. The soil samples (nonflooded [60% water-holding capacity] and flooded) were treated first with technical parathion (20 μg/g) and then after 10 days with ring-labeled [14C]parathion. In unplanted soil, less than 5.5% of the 14C in the parathion was evolved as 14CO2 in 15 days under both flooded and nonflooded conditions. In soil planted with rice, 9.2% of the radiocarbon was evolved as 14CO2 under nonflooded conditions, and 22.6% was evolved under flooded conditions. These results suggest that soil planted with rice permits significant ring cleavage, especially under flooded conditions. 相似文献
13.
1. Rats were starved for 48hr. or fed for 1 week on a high-fat or a high-carbohydrate diet. The effects of these dietary alterations on the rate of production of 14CO2 from trace amounts of [U-14C]glucose, [1-14C]palmitate or [1-14C]acetate administered intravenously were studied. 2. The oxidation of [14C]glucose was most rapid in the carbohydrate-fed condition and was decreased significantly and to the same extent after starvation and after feeding with fat. 3. Under all dietary regimes studied the maximum rate of elimination of 14CO2 from [14C]palmitate occurred within a few minutes after injection, but considerably more was oxidized after starvation and feeding with fat than after feeding with carbohydrate. 4. Alterations in diet had no effect on the oxidation and high recovery of administered [14C]acetate as 14CO2. 5. Graphical analysis showed the presence of several exponential components in the 14CO2-elimination curves. 6. In all studies a marked similarity in oxidative pattern was noted between the starved and the fat-fed rat. 相似文献
14.
《Phytochemistry》1987,26(11):2923-2927
The action of boron on phospholipid composition and synthesis in roots and microsomes from sunflower seedlings has been studied. The fatty acid composition and relative amounts of individual molecular species of phospholipids in roots and microsomes were very similar. In both the content of phospholipids was decreased and the relative levels of their component fatty acids changed by treatment with 50 ppm of boron. This concentration of boron in the culture medium was found to inhibit the in vivo [1-14C] acetate incorporation into root lipids and that of [Me-14C] choline into phosphatidylcholine of root microsomes. Cytidine-5-diphospho (CDP)-[Me-14C] choline incorporation into phosphatidylcholine of isolated microsomes was also inhibited by 50 ppm of boron when present in the growth medium of seedlings. These results indicate that the decrease in phosphatidylcholine labelling from [14C] choline observed when root microsomes were treated with boron would be caused by a decrease in CDP-choline phosphotransferase activity. 相似文献
15.
In G2 peas (Pisum sativum L.) apical senescence occurs only in long days (LD), and indeterminate growth is associated with elevated gibberellin (GA) levels in the shoot in short days (SD). Metabolism of GA12 aldehyde was investigated by feeding shoots grown in SD or LD with [14C]GA12 aldehyde through the cut end of the stem for 0.5 to 6 hours in the light and analyzing the tissue extract by high performance liquid chromatography. More radioactive products were detected than can be accounted for by the two GA metabolic pathways previously known to be present in peas. Three of the major products appear to be GA conjugates, but an additional pathway(s) of GA metabolism may be present. The levels of putative C20 GAs, [14C]GA53, [14C]GA44, [14C]GA19, and/or [14C] GA17, were all elevated in SD as compared to LD. Putative [14C]GA, was slightly higher in LD than in SD. Putative [14C]GA53 was a major metabolite after 30 minutes of treatment in SD but had declined after longer treatment times to be replaced by elevated levels of putative [14C] GA44 and [14C]GA19/17. Metabolism of GA20 was slow in both photoperiods. Although GA20 and GA19 are the major endogenous GAs as determined by gas chromatography-mass spectrometry, putative [14C]GA20 and [14C]GA19 were never major products of [14C]GA12 aldehyde metabolism. Thus, photoperiod acts in G2 peas to change the rate of GA53 production from GA12 aldehyde, with the levels of the subsequent GAs on the 13-OH pathway being determined by the amount of GA53 being produced. 相似文献
16.
In tobacco seedlings (Nicotiana tabacum L.), glucose from supplied uridine diphosphate-[U-14C]glucose was first incorporated into steryl glycosides and later into acylated steryl glycosides. However, when [14C]cholesterol was used as substrate, the acylated steryl glycosides became labeled earlier than the steryl glycosides. With [14C]cholesteryl glucoside as substrate, most of the radioactive label was recovered as free sterol, and the acylated steryl glycosides were not readily labeled; however, palmitoyl [14C]cholesteryl glucoside was rapidly converted to steryl glycoside. In feeding experiments with free sterol, an unknown, highly radioactive steroid component was isolated. Incorporation of radioactivity into the unknown occurred before the acylated steryl glycosides were labeled. 相似文献
17.
Degradation of (+)-isothujone biosynthesized by Tanacetum vulgare or Thuja plicata from acetate-[1-14C], -[2-14C] and -[2-3H3] or from CO2-[14C] at physiological concentration revealed a pattern of asymmetric labelling whereby tracer predominantly (72–98% resided in that part of the skeleton derived from IPP. This is similar to the patterns previously obtained for uptake of MVA-[2-14C] but differed from those reported in other species with acetate-[14C] as precursor. Within the IPP-derived moiety the 3 parts derived from acetate units were not equivalently labelled. Partial degradations of geraniol and (+)-pulegone formed in Pelargonium graveolens and Mentha pulegium after uptake of 14C-labelled acetate or CO2 showed that the C-2 units of the skeletons of these monoterpenes were also labelled to widely differing extents and these patterns persisted over a range of feeding and seasonal conditions. These results suggest that metabolic pools of acetyl-CoA and/or acetoacetyl-CoA exist in these plants. The general occurrence of such pools and the consequent nonequivalent labelling patterns in secondary metabolism could invalidate biosynthetic conclusions drawn from partial degradations of labelled natural products. 相似文献
18.
4,2′,4′-Trihydroxychalcone- [carbonyl-14C], formononetin- [Me-14C] and texasin- [Me-14C] were all good precursors of afrormosin (7-hydroxy-6,4′-dimethoxyisoflavone) in Onobrychis viciifolia seedlings, and a biosynthetic pathway involving these intermediates is proposed. 2′,4′-Dihydroxy-4-methoxychalcone- [carbonyl-14C] and daidzein-[carbonyl-14C] were poor precursors. Incorporations into formononetin were also recorded. 相似文献
19.
A quantitative triterpene analysis was made of latex stem tissue of Euphorbia lathyris. Young plants seedlings of E. lathyris were incubated with various labelled precursors. Incorporation into triterpenes was obtained from [2-14C]mevalonic acid, [1-14C]acetate, [3-14C]pyruvate, [U-14C]sucrose, [U-14C]glucose, [U-14C]xylose, [U-14C]glyoxylate, [2,3-14C]succinic acid, [1-14C]glycerol [U-14C]serine. Both sugars tyrosine appeared to be effective precursors in DOPA synthesis inside the laticifers. Exogenously supplied mevalonic acid was only involved in triterpene synthesis outside the laticifers. GC-RC of triterpenes synthesized from [U-14C]glucose revealed the origin of these compounds in the latex. The labelled triterpenes obtained after incorporation of the other mentioned labelled precursors were only partly synthesized in the laticifers. For quantitative data on latex triterpene synthesis seedlings were incubated with [U-14C]sucrose, [U-14C]glucose, [U-14C]xylose [1-14C]acetate in the presence of increasing amounts of unlabelled substrate. From the amount of 14C incorporated into the triterpenes the amount of substrate directly involved in triterpene synthesis was calculated, as was the absolute triterpene yield. Sucrose showed the highest triterpene yield, equivalent to the daily increase of the triterpene content of growing seedlings. The possible significance of the other precursors in triterpene synthesis in the laticifers is discussed. 相似文献
20.
《Phytochemistry》1986,25(12):2779-2781
Six-day-old tobacco (Nicotiana tabacum) and barley (Hordeum vulgare) seedlings rapidly incorporated and metabolized exogenously supplied [4-14C]sitosterol but neither plant was able to convert it into stigmasterol. However, a sterol metabolite was isolated from both species and the acetate derivative was slightly more polar, on AgNO3—silica gel TLC, than stigmasteryl acetate. A similar metabolite was also obtained with [4-14C]cholesterol, indicating a general metabolic reaction of plants to exogenous sterols. Both species incorporated [2-14C]mevalonic acid into sitosterol and stigmasterol. We suggest that in vascular plants, whether monocotyledons or dicotyledons, the pathway of stigmasterol biosynthesis is not via sitosterol but through a common precursor which is derived from mevalonic acid. 相似文献