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1.
3rß-Fluorogibberellin A9 (3rß-fluoro-GA9),3rßfluoro-GA20, 3rß-fluorodeoxygibberellinC (3rß-fluoro-DGC) and 13-fluoro-GA9 were prepared,and their effects on plant growth and gibberellin (GA) 3rß-hydroxyIaseswere examined. 3rß-Fluoro-GA9 and 3rß-fluoro-GA20promoted the growth of dwarf rice (Oryza sativa L. cv. Tan-ginbozu)seedlings to three times higher than the control seedlings ata dosage of 3 µ plant–1, and 3rßfluoro-DGCto twice higher at the same dosage. 3rßg-Fluoro-GA9was active in cucumber (Cucumis sativus L.) hypocotyl assay,its activity being about one-thirtieth as much as that of GA4.3rß-Fluoro-GAs were active per se in promoting theshoot elongation of rice. 3rß-Fluoro-DGC inhibitedthe 3rß-hydroxylation of [3H2]GA9 to [3H]GA4 by GArß-hydroxylase from bean (Phaseolus vulgaris L.),but 3rß-fluoro-GA9 and 3rß-fluoro-GA20 didnot show any effects on the enzyme activity. These 3rß-fluoro-GAsalso showed no or only a weak inhibitory effect on the rß-hydroxylasefrom pumpkin (Cucurbita maxima L.). 13-Fluoro-GA9 promoted growthof rice and cucumber seedlings, and inhibited the 3rß-hydroxylasesfrom both bean and cucumber. 13-Fluoro-GA9was converted into13-fluoro-GA4 and 2,3-didehydro-13-fluoro-GA9, in a cell-freesystem from bean, and conversion of 13-fluoro-GA9 into 13-fluoro-GA4was also observed in a cell-free system from pumpkin. Theseresults suggest that 13-fluoro-GA9 is one of the substratesof GA 3rß-hydroxy-lases, and that 13-fluoro-GA9 isactive as a result of the conversion to 13-fluoro-GA4 in riceand cucumber seedlings. (Received October 27, 1997; Accepted March 13, 1998)  相似文献   

2.
Inhibition of the biosynthesis of gibberellins by prohexadione,3,5-dioxo-4-propionylcyclo-hexanecarboxylic acid, was studiedwith cell-free systems derived from immature seeds of Cucur-bitamaxima, Phaseolus vulgaris and Pisum sativum. Prohexadione,at a concentration of 10–4 M, inhibited C-7 oxidationof GA12-aldehyde, C-20 oxidation of GA15, conversion of C20-gib-berellinsto C19-gibberellins, 3ß-hydroxylation, 2,3-dehydrogenationof GA20, 2,3-epoxidation of GA5 and 2ß-hydroxylationof GA9 and GA20. The 3ß-hydroxylase activity appearedto be more sensitive to prohexadione than were the C-20 oxygenaseand the 2ß-hydroxylase activities. The conversionof mevalonic acid to GA12-aldehyde and the 13-hydroxylationof GA12 were not affected by prohexadione at a concentrationof 3 ? 10–4 M. All of the steps inhibited by prohexadioneare oxidation steps catalyzed by soluble enzymes that require2-oxoglutarate, Fe2+ and oxygen, and all of them occur distalto the synthesis of GA12-aldehyde in the biosynthesis of gibberellins. (Received April 4, 1990; Accepted September 14, 1990)  相似文献   

3.
Partial submergence or treatment with either ethylene or gibberellicacid (GA3 induces rapid growth in deepwater rice (Oryza sativaL.). We correlated the synthesis of two cell wall componentswith two phases of internodal elongation, namely (13,14)-ß-glucanformation with cell elongation and lignification with differentiationof the secondary cell wall and cessation of growth. The contentof ß-glucan was highest in the zone of cell elongationin internodes of air-grown plants and plants that were inducedto grow rapidly by submergence. In the intercalary meristemand in the differentiation zone of the internode, ß-glucanlevels were ca. 70% lower than in the zone of cell elongation.The outer cell layers, enriched in epidermis, contained moreß-glucan in submerged, rapidly growing internodesthan in air-grown, control internodes. The ß-glucancontent of the inner, parenchymal tissue was unaffected or slightlylowered by submergence. The epidermis appears to be the growth-limitingstructure of rapidly growing rice internodes. We hypothesizethat elevated levels of ß-glucan contribute to elongationgrowth by increasing the extensibility of the cell wall. Lignificationwas monitored by measuring the content of lignin and the activitiesof two enzymes of the lignin biosynthetic pathway, coniferylalcohol dehydrogenase (CAD) and phenylalanine ammonia-lyase(PAL), in growing and non-growing regions of the internode.Using submerged whole plants and GA3-treated excised stem segments,we showed that lignin content and CAD activity were up to sixfoldlower in newly formed internodal tissue of rapidly growing ricethan in slowly growing tissue. No differences were observedin parts of the internode that had been formed prior to inductionof growth. PAL activity was reduced throughout the internodeof submerged plants. We conclude that lignification is one ofthe processes that is suppressed to permit rapid growth. 1 This work was supported by the National Science Foundationthrough grants No. DCB-8718873 and DCB-9103747 and by the Departmentof Energy through grant No. DE-FGO2-90ER20021. M.S. was therecipient of a fellowship from the Max Kade Foundation.  相似文献   

4.
The relationship between coleoptile elongation and survivalvs. alcoholic fermentation of rice under anoxia is examinedusing eight cultivars differing in submergence tolerance. Anoxiawas imposed on either 1 or 4 d aerated seeds either by N2 flushingsubmerged tissues or by incubating tissues in stagnant deoxygenatedagar at 0·1% w/v; the latter simulated the stagnant conditionsof waterlogged soil. Two cultivars that were most tolerant tosubmergence also had the greatest tolerance to anoxia, whilea submergence intolerant cultivar was also intolerant to anoxia. Coleoptile growth under anoxia was related to rates of ethanolsynthesis (RE), however differences between growth during anoxiaand survival after anoxia indicated that post-anoxic injurymay also be important in rice seeds exposed to anoxia. The correlationbetween coleoptile growth and RE measured on a tissue basisusing intact seeds was r2 = 0·67 among six varietiesover 0-3 d anoxia. This correlation improved to about r2 = 0·85using RE of (embryos plus coleoptiles) over 0-3 d, or coleoptilesat 3 d after anoxia. Coleoptile growth of individual seeds wasusually poorly correlated to RE in these cultivars at 2-3 dafter anoxia. When coleoptiles of similar lengths were obtainedfrom different cultivars using 4 d aerated seeds, there weredifferences in RE and coleoptile growth which were related tocoleoptile growth during 3 or 5 d anoxia, either on a tissue(r2 = 0·85) or a fresh weight basis (r2 = 0·70-0·97respectively). Results are discussed in relation to factorswhich may limit ethanol synthesis in rice exposed to anoxiaand the importance of growth to the survival of seeds and matureplants during submergence in the natural environment.Copyright1994, 1999 Academic Press Anoxia, ethanol, alcoholic fermentation, Oryza sativa L., rice, submergence  相似文献   

5.
-Mannosidase and ß-N-acetylglucosaminidase were purifiedfrom extracts of cotyledons of germinating Pisum sativum L.A 13-fold purification of a-mannosidase free from ß-N-acetylglucosaminidaseactivity was achieved by precipitation in ammonium sulphate,column chromatography on DEAE-cellulose, and treatment with2 M pyridine. ß-N-Acetylglucosaminidase was purified200-fold by the use of (NH4)2SO4, and chromatography on ConcanavalinA1-Sepharose and Sephacryl-200. This preparation showed no measurablecontamination by -mannosidase activity. Both glycosidases appearto be glycoproteins and demonstrate optimal activity at pH valuesof 4.0–4.5. Both glycosidases appear to have very similarmolecular weights, with -mannosidase being slightly larger thanß-N-acetylglucosaminidase. An extensive search forthe activity of aspartylglycosylamine amido hydrolase in peacotyledons proved unsuccessful.  相似文献   

6.
Deoxygibberellin C (DGC), a C/D ring-rearranged isomer of GA20,was shown to inhibit the conversion of [2,3-3H2]GA9 to [2-3H]GA4by gibberellin 3ß-hydroxylase from immature seedsof Phaseolus vulgahs. Deoxygibberellin C inhibited the promotionof growth by exogenously applied GA20 of rice (Oryza sativaL.) seedlings. Evidence is also presented that DGC is a competitiveinhibitor of the 3ß-hydroxylase from P. vulgaris.However, DGC only weakly inhibited the conversion catalyzedby the 3ß-hydroxylase from Cucurbita maxima at highconcentrations, and it did not inhibit the promotion of growthby exogenously applied GA9 of cucumber (Cucumis sativus) seedlings.These results suggest that the 3ß-hydroxylases fromP. vulgaris and C. maxima have different structural requirementswith respect to their substrates. 16-Deoxo-DGC also inhibitedcatalysis of the same conversion by 3ß-hydroxylasefrom P. vulgaris, and it slightly inhibited the conversion catalyzedby the enzyme from C. maxima. Application of 16-deoxo-DGC causedthe promotion of the growth of seedlings of both rice and cucumber. 3 Present address: Genetic Engineering Center, Korea Instituteof Science and Technology, Daejeon 305–606, Korea 4 Present address: Department of Agricultural Chemistry, UtsunomiyaUniversity, Utsunomiya-shi, Tochigi, 321 Japan (Received September 25, 1990; Accepted December 17, 1990)  相似文献   

7.
Immature embryos (stage I) and cotyledonary somatic embryos(stage III) of black spruce [Picea mariana (Mill) B.S.P.] werebombarded with tungsten particles coated with a gene constructcontaining the fusion of gus:: nptll. GUS (ß-glucuronidase)activity was monitored histochemically with X-gluc giving ablue colour where transient gene expression was detected inthe bombarded tissues. A high transient expression of gus wasobserved in stage I embryo cultures 2 d after bombardment (202GUS foci per 300 mg tissue). GUS activity had substantiallydiminished in this material 14 d after bombardment, when grownin liquid LP maintenance medium containing BA (4.4µM),2,4-D (9µM) and 1% sucrose. However, when stage I embryoswere cultured on LP maturation medium containing BA (40 µM),IBA (1 µM), 3.4% sucrose and 0.8% agar, GUS activity after2 d was 335 GUS foci per 300 mg tissue, and the activity wasdetected until 30 d after bombardment. With stage III somaticembryos cultured on LP maintenance medium, 92% showed GUS activity2d after bombardment (16 GUS foci per embryo), and 31 % showedactivity 30 d after bombardment (4 GUS foci per embryo). GUSactivity was still evident in 12% of the embryos (2 GUS fociper embryo) 45 d after bombardment. Key words: Black spruce, gus = E. coli geneuid A encoding ß-glucuronidase, nptll = gene encoding neomycin phos-photransferase, somatic embryos  相似文献   

8.
Lupinus albus L. developing cotyledons 35 d after floweringcontained a major polypeptide of-average Mr 64000, immunologicallyrelated to conglutin ß, the 7S storage globulin ofthis seed. This polypeptide decreased during seed maturation,without completely disappearing in the mature seed. This dropwas accompanied by the formation of polypeptide fragments typicalof the mature conglutin ß. The 64000 polypeptide hasbeen identified as the precursor polypeptide of conglutin ß. Undenatured conglutin ß precursor, purified by ionexchange chromatography and size exclusion chromatography, showedsurface and association properties identical to the mature conglutinß molecule. The precursor oligomer, of Mr 190000,consisted of an association of three 64000 subunits. They stronglyreacted with concanavalin A indicating the presence of covalentlylinked carbohydrate. Tryptic treatment of the undenatured conglutin ß precursorled to the accumulation of a relatively stable 59000 polypeptidewhich was cleaved later on and produced three large polypeptidefragments differing from the mature conglutin ß polypeptides. Key words: Conglutin ß, precursor, developing seeds, Lupinus albus L.  相似文献   

9.
Gibberellin 3/ß-hydroxylase,a 2-oxoglutarate-dependentdioxygenase that catalyzes the hydroxylation of GA20 to GA1,was purified 313-fold from immature seeds of Phaseolus vulgarisL. The mol wt of the enzyme was estimated to be 42,000 by gelfiltration HPLC and SDS-polyacrylamide gel electrophoresis.The enzyme exhibited maximum activity at pH 7.7. The Km valuesfor [2,3-3H]GA20 and [2,3-3H]GA, were 0.29µu and 0.33µm, respectively. The enzyme requires 2-oxoglutarate asa cosubstrate; the Km value for 2-oxoglutarate was 250µMusing [3H]- GA20 as a substrate. Fe2+ and ascorbate significantlyactivated the enzyme at all purification steps, while catalaseand BSA activated the purified enzyme only. The enzyme was inhibitedby divalent cations Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Hg2+.3ß-Hydroxylation of [3H]- GA20 was also inhibitedby non-radioactive GA5, GA9,GA15, GA20 and GA44. The possiblesite of 3ß-hydroxylation in gibberellin biosynthesisis discussed in terms of the substrate specificity of partiallypurified gibberellin 3ß-hydroxylase. (Received February 29, 1988; Accepted June 3, 1988)  相似文献   

10.
The gene encoding a ß-galactosidase from Xanthomonasmanihotis was cloned into Escherichia coli. The gene resideson a 2.4 kb DNA fragment which was isolated from a partial Sau3Alibrary in the cloning vector pUC19 using 5-bromo-4-chloro-3-indolyl-ß-D-galactopyranoside(X-gal) as the selection. The enzyme produced by the clone hasa specificity for ß1-3->ß1-4-linked galactose.The nucleotide sequence of the gene was determined. The deducedprotein sequence contained 597 amino acids yielding a monomericmolecular mass of 66 kDa. The cloned ß-galactosidaseshowed no similarity to any known prokaryotic ß-galactosidase.However, extensive similarity was observed with eukaryotic ß-galactosidasesfrom animals, plants and fungi. The strongest similarity waswith the ß-galactosidases found hi the human and mouselysosomes (42 and 41% identity, respectively). Alignment ofthe X.manihotis and eukaryotic ß-galactosidase sequencesrevealed seven highly conserved domains common to each protein.Additionally, Domain 1 in X.manihotis showed similarity to regionswithin catalytic domains from seven xylanases and cellulasesbelonging to family 10 of glucosyl hydrolases. A region spanningDomain 2 showed similarity to the catalytic domain of endo ß1-3glucanases from tobacco and barley. cellulase ß-galactosidase GM$$$gangliosidosis Morquio B syndrome Xanthomonas  相似文献   

11.
Trends in several photosynthetic parameters and their responseto changed growth light were followed for 15 d in leaves ofyoung birch saplings using a rapid-response gas exchange measuringequipment. These in vivo measurements were compared to biochemicalassays that were made from the same leaves after the gas exchangestudies. The measurements were made on leaves that were selectedprior to the study and were at that time of similar age. Forthe first 7 d the photosynthetic parameters were followed fromthe growth conditions of moderate light (200 µmol m–2s–1; referred to as controls later in the text). On day7 some of the saplings were transferred to grow either underhigh (450 µmol m–2 s–1; referred to as highlight plants) or low (75 µmol m–2 s–1; referredto as low light plants) light and the capability of the preselectedleaves for acclimation was followed for 6 d. For comparison,at the end of the experiment the measurements were made on bothcontrols and on young leaves that had developed under high andlow light. Generally the in vivo measured rate of CO2 uptake (gross photosynthesis)both at 310 ppm CO2 and 2000 ppm CO2 corresponded very wellto the biochemically determined CO2 fixation capacity in vitroafter rapid extraction (measured as the initial and total activityof Rubisco, respectively). However, if the flux of CO2 intothe chloroplasts was limited by the closure of the stomata,as was the case of the high light plants, then the in vitromeasured Rubisco activity was greater than the in vivo measuredCO2 uptake. Vmax, calculated from the mesophyll conductanceat 1% O2, exceeded the initial activity of Rubisco (assayedat saturating RuBP and CO2) constantly by 60%. The catalyticactivity of Rubisco in birch leaves was overall very low, evenwhen calculated from the total activity of Rubisco (Kcat 0.63–1.18 s–1), when compared to herbaceous C3 species. Signs of light acclimation were not observed in most of thephotosynthetic parameters and in chloroplast structure whenmature birch leaves were subjected to changes in growth lightfor 6 d. However, the change of the growth light either to highor low light caused day-to-day fluctuations in most of the measuredphotosynthetic parameters and in the case of the high lightplants signs of photoinhibition and photodestruction were alsoobserved (decrease in the amount of chlorophyll and increasein chlorophyll a/b ratio). As a result of these fluctuationsthese plants achieved a new and lower steady-state conditionbetween the light and dark reactions, as judged from the molarratio of RuBP to Rubisco binding site. Key words: Acclimation, photosynthesis, light, Rubisco, birch  相似文献   

12.
The relationship between autolytic degradation of ß(1–3),(1–4)-D-glucanand acid pH-induced extension of isolated Zea mays cell wallshas been investigated using a constant-load extension technique.Acidic buffer (4.5) was able to induce an additional extension(Ea) on cell walls already extended at pH 6.8 buffer under a20 g-mass load, indicating that the additional extension (Ea)was the parameter that better represented the effect of thedifferent treatments on the mechanical properties of maize coleoptilecell walls. The additional extension in response to acidic pHwas higher when cell walls had been previously autolysed for24 h at pH 5.5. Furthermore, the acid-pH effect was dependenton the presence during the constant load extension of some thermo-labilefactors, suggesting the participation of expansins. Acid pHincreased Ea of native cell walls through an increase in theplastic extension (Ep) in agreement with a one step mechanismleading directly to irreversible (plastic) wall extension assuggested by Cosgrove (1977). The autolytic degradation of ß(1–3),(1–4)-D-glucan was also able to modify the mechanicalproperties of maize coleoptile cell walls increasing its elasticextension (Ee) in response to pH 4.5 buffer but that modificationonly leads to an increase in wall extension when expansins areactive, suggesting a cooperation between ß-glucanturnover and expansin action. (Received August 5, 1998; Accepted March 16, 1999)  相似文献   

13.
This study investigated how CO2and temperature affect dry weight(d.wt) accumulation, total nonstructural carbohydrate (TNC)concentration, and partitioning of C and N among organs of twoimportant grasses of the shortgrass steppe,Pascopyrum smithiiRydb. (C3) andBouteloua gracilis(H.B.K.) Lag. ex Steud. (C4).Treatment combinations comprised two temperatures (20 and 35°C)at two concentrations of CO2(380 and 750 µmol mol-1),and two additional temperatures of 25 and 30°C at 750 µmolmol-1CO2. Plants were maintained under favourable nutrient andsoil moisture and harvested following 21, 35, and 49d of treatment.CO2-induced growth enhancements were greatest at temperaturesconsidered favourable for growth of these grasses. Comparedto growth at 380 µmol mol-1CO2, final d.wt of CO2-enrichedP.smithiiincreased 84% at 20°C, but only 4% at 35°C. Finald.wt ofB. graciliswas unaffected by CO2at 20°C, but wasenhanced by 28% at 35°C. Root:shoot ratios remained relativelyconstant across CO2levels, but increased inP. smithiiwith reductionin temperature. These partitioning results were adequately explainedby the theory of balanced root and shoot activity. Favourablegrowth temperatures led to CO2-induced accumulations of TNCin leaves of both species, and in stems ofP. smithii, whichgenerally reflected responses of above-ground d.wt partitioningto CO2. However, CO2-induced decreases in plant tissue N concentrationswere more evident forP. smithii. Roots of CO2-enrichedP. smithiihadgreater total N content at 20°C, an allocation of N below-groundthat may be an especially important adaptation for C3plants.Tissue N contents ofB. graciliswere unaffected by CO2. Resultssuggest CO2enrichment may lead to reduced N requirements forgrowth in C3plants and lower shoot N concentration, especiallyat favourable growth temperatures. Acclimation to CO2; blue grama; Bouteloua gracilis ; carbohydrate; climate change; global change; grass; growth; growth temperature optima; nitrogen; N uptake; Pascopyrum smithii; western wheatgrass  相似文献   

14.
The major isoenzymes of -mannosidase (EC 3.2.1.24 [EC] ) and ß-galactosidase(ECf 3.2.1.23 [EC] ) have been separated from cotyledons of gardenpea, Pisum sativum L. (Vicieae), chick pea, Cicer arietinumL. (Cicereae), and cowpea, Vigna unguiculata (L.) Walp. (Phaseoleae).Some of their properties have been determined, including pHoptima, Km values for p-nitrophenyl glycosidc substrates, andthe effects of several inhibitors. Swainsonine, an indolizidinealkaloid, was the most effective inhibitor of mannosidase 1,with I30 values of 5.6 x 10–8 M (cowpea), 1x 10–7M (chick pea) and 2.9 x 19–7 M (pea). The most effectiveinhibitor of ß-galactosidase 2 from all sources wasD-galactonic acid-1,4-lactonwe (-lactone), with Ki values rangingbetween 3.0 and 3.9x 10–3 M. An inhibitor of the E. coliß-galactosidose, p-aminophenyl thio-ß-D-galactopyranoside,did not inhibit any of the legume ß-galctosidases;rather it enhanced the activites of the enzymes from chick peaand cowpea cotyledons. Etiolated hull and seed tissues frompea pods developing in darkness contained similar acid glycosidaseactivities to normal green tissues, thus the chloroplast isan unlikely location for ß-galactosidase 2. The majorß-galactosidasesdetected with an indigogenic substrate (5-bromo-4-chloro-3-indoxyl-ß-D-galactopyranoside)following gel electrophoresis of extracts from pea hull, seedcoats and cotyledons appeared to be different from ß-galactosidase2. Acid glycosidase, cotyledon, isoenzyme, -lactone, legume, swainsonine  相似文献   

15.
A membrane fraction from flax cells was able to incorporate[14C]galactose from UDP-D-[14C]galactose in vitro. The productsof the reaction, characterized by methylation analysis, consistedof a rß-1,4-galactan (solubilized mainly in water)and a rß-1,3- rß-1,6-galactan (solubilizedmainly in alkali). These results indicated the presence of severalgalactan synthase complexes, as did a profile of the relationshipbetween pH and activity which revealed both a maximum at pH6.5 and a shoulder at pH 8. Moreover, galactan synthase activitieswere found at two densities: 1.125 g cm–3 (Golgi membranes)and 1.07–1.08 g cm–3 (corresponding to low-densityvesicles). Partial characterization of one enzymatic system (maximaly activeat pH 8 in the presence of 5 mM MgCl2) was achieved. The Kmfor UDP-galactose and Vmax were 38 µM and 4.5 nmol h–1(mg protein)–1, respectively. (Received June 6, 1993; Accepted September 22, 1993)  相似文献   

16.
Damage and degradation of cellular proteins is observed duringage-induced seed deterioration. L-Isoaspartyl protein methyltransferase(EC 2.1.1.77 [EC] ) is an enzyme hypothesized to play a role in limitingand repairing age-induced damage to proteins. Tomato (Lycopersiconesculentum Mill. ‘New Yorker’) seeds were assayedfor changes in L-isoaspartyl methyl-transferase activity duringaccelerated ageing and after osmotic priming. Accelerated ageingof seeds for 1–4 d at 45C and 100% relative humidityreduced germination from 94% to 71%, increased the mean timeof germination (MTG) from 2.4 to 5.8 d, and was accompaniedby a correlative decrease in L-isoaspartyl methyltransferaseactivity (r2=0.90). Aged and untreated seeds were primed for7 d at 20C in darkness using aerated solutions of 3% KNO3 orpolyethylene glycol 8000 (PEG) with equivalent osmotic potential(–1.25 MPa). Priming with KNO3 decreased the MTG, butdid not improve germination percentage for untreated seeds.Priming did not affect L-isoaspartyl methyltransferase activityin untreated seeds, but restored activity in aged seeds primedin KNO3 to levels near that of untreated seeds. Priming withPEG did not effectively improve the MTG or increase L-isoaspartylmethyltransferase activity. During germination, L-isoaspartylmethyltransferase activity remained constant for 48 h post-imbibitionand then declined, suggesting that the enzyme was developmentallyregulated and inactivated or degraded as radicle emergence occurred. Key words: L-Isoaspartyl methyltransferase, protein repair, seed priming, accelerated ageing, Lycopersicon esculentum  相似文献   

17.
The circadian rhythm of CO2 output in leaves of Bryophyllumfedtschenkoi damps out after 3–4 d in continuous darknessand a CO2-free air stream at 15°C. The rhythm is reinitiatedafter a single exposure to white light of 2, 4, 6 or 8 h duration,damps out again after a further 3–4 d and can be reinitiatedfor a second time by a further exposure to light. During the exposure to light there is a burst of CO2 outputconsistent with the decarboxylation of malate, and the rhythmbegins afterwards with an initial high rate of CO2 fixation.Malate gradually accumulates in the leaves in continuous darknessto attain a maximum value (35 mol m–3) at the time whenthe circadian rhythm disappears, and decreases to a low value(19 mol m–3) after a 4 h exposure to light which reinitiatesrhythmicity. These results support the hypothesis that damping of the rhythmof CO2 output in continuous darkness is due to the accumulationof malate in the leaf cells, eventually reaching such a levelthat its removal from the cytoplasm into the vacuole cannottake place, with the result that PEPc activity, upon which therhythm of CO2 output depends, remains allosterically inhibited. Key words: CAM, circadian rhythm, Bryophyllum, CO2-fixation, malate metabolism  相似文献   

18.
The flower-inducing activities in Lemna paucicostata 151 offour major metabolites of benzoic acid (N-benzoyl aspartate,benzyl 6-O-ß-D-apiofuranosyl-O-ß-D-glucopyranoside,O-benzoyl isocitrate and O-benzoyl malate) were measured, andthe effects on the uptake and metabolism of benzoic acid dueto change in the level of the benzoic acid concentration orto the addition of plant hormones were investigated. N-Benzoylaspartate had weak activity, and O-benzoyl isocitrate and malatehad fairly strong activities, while benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranosideshowed no activity. As the concentration of benzoic acid rose,the ratio of N-benzoyl aspartate increased and that of benzyl6-O-ß-D-apiofuranosyl-O-ß-D-glucopyranosidedecreased. GA3 and IAA, inhibitors of flower induction by benzoicacid, seemed to promote conversion to N-benzoyl aspartate insteadof to benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranoside.The conversion to N-benzoyl aspartate was considered to be adetoxification process and that to benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranosidemay be directly related to flower induction in Lemna. (Received November 2, 1987; Accepted January 23, 1988)  相似文献   

19.
A cytochrome b6f complex was isolated and purified from Spirulinasp. The complex was solubilized with n-heptyl ß-D-thioglucosideand chromatographed on a DEAE-Toyopearl 650M column. The purifiedcomplex contained a small amount of chlorophyll and carotenoid.At least four polypeptides were present in the complex: cytochromef (29 kDa), cytochrome b6(23 kDa), iron-sulfur protein (ISP,23 kDa), and a 17 kDa polypeptide. Each polypeptide was separatedfrom the complex treated with 2-mercaptoethanol or urea. Theabsorption spectra of cytochrome b6 and cytochrome f were similarto those of Anabaena and spinach as expected. The complex wasactive in supporting ubiquinol-cytochrome c oxidoreductase activity.Fifty percent inhibition of the activity was accomplished by1 µM dibromothymoquinone (DBMIB). The Km values for ubiquinol-2and cytochrome c (horse heart) were 5.7 µM and 7.4 µM,respectively. (Received August 15, 1988; Accepted November 14, 1988)  相似文献   

20.
Lymphocytic ß1,4-galactosyltransferase (ß1,4-GalTase,EC 2.4.1.38 [EC] ) activity was measured in B cells using a neoglycoprotein,N-acetylglucosamine-phenylisothlocyanate-bovine serum albumin(GlcNAc-pITC-BSA), as an acceptor substrate in a novel enzyme-linkedimmunosorbent assay (ELISA)-based method. This assay provedto be much simpler to use than the lengthy and expensive radiochemicalassays commonly used, and has the additional advantage thatit specifically detects the enzyme mediating transfer via theGalß1,4GlcNAc linkage. A F(ab')2 antibody againstGalTase was able to specifically inhibit the reaction. Greatersensitivity for ß1,4-GalTase activity was obtainedusing GlcNAc-pITC-BSA as an acceptor substrate rather than ovalbumin.Low levels of ß-galactosidase activity were detectablein lymphocyte cell lysates at acidic pH, although such activitywas not detectable at the neutral pH used in the ß1,4-GalTaseactivity assay. Using this assay with the GlcNAc-pITC-BSA acceptor,similar ß1,4-GalTase activities were observed in CD19+B cells from patients with rheumatoid arthritis (RA) to thoseseen in normal control individuals. ELISA ß1,4-galactosyltransferase lymphocyte neoglycoprotein radiochemical  相似文献   

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