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1.
Wheat plants were grown in a controlled environment with daytemperatures of 18 ?C and with 500 µ Einsteins m–28–1 of photosynthetically active radiation for 16 h. Beforeanthesis and 2 to 3 weeks after, rates of net photosynthesiswere measured for leaves in 2 or 21% O2 containing 350 vpm CO2at 13, 18, 23, and 28 ?C and with 500 µEinsteins m–2s–1 of photosynthetically active radiation. Also, underthe same conditions of light intensity and temperature, therates of efflux of CO2 into CO2-free air were measured and,for mature flag leaves 3 to 4 weeks after anthesis, gross andnet photosynthesis from air containing 320 vpm 14CO2 of specificactivity 39?7 nCi µmol–1. When the O2 concentration was decreased from 21 to 2% (v/v)the rate of net photosynthesis increased by 32 per cent at thelowest temperature and 54 per cent at the highest temperature.Efflux of CO2 into CO2-free air ranged from 38 per cent of netphotosynthesis at 13 ?C to 86 per cent at 28 ?C. Gross photosynthesis,measured by the 14C assimilated during 40 s, was greater thannet photosynthesis by some 10 per cent at 13 ?C and 17 per centat 28 ?C. These data indicate that photorespiration was relativelygreater at higher temperatures.  相似文献   

2.
A technique is described for the isolation of purified nucleifrom suspension culture cells of Acer pseudoplatanus. This involvesa grinding medium containing 70% (v/v) glycerol, 1 mM Mg2+,2 mM Ca2+, and Tris buffer at pH 7.8, prestorage and disruptionof the cells at –20 °C in a Potter-Elvehjem homogenizer,and purification by filtration and centrifugation in the presenceof Triton X-100. The nuclear yield is c. 25% as assessed bynuclear count or DNA estimation and the nuclei are active inthe RNA synthesizing system of Tautvydas (1971). When the histones of these nuclei are extracted in H2SO4 andprecipitated by ethanol, 113 µg histone is obtained perµg nuclear DNA and the histone fraction contains 22% basicamino acids and has a lysine: arginine ratio of 2.6. Acid-ureagel electrophoresis shows the presence of five major histones(H1, H2A, H2B, H3, and H4 in sequence from anode to cathode)having respectively molecular weights of 24 500, 13 500, 13300, 12 800, and 11 000. There is very good correspondence betweencalf thymus histones H3 (reduced form) and H4 and two of theseAcer histones. The other Acer histones differ from the calfthymus histones H1, H2A, H2B in molecular weight but can beprovisionally equated with these by a newly developed differentialstaining reaction. Calf thymus histone H2A appears to be lessrich in lysine than the corresponding Acer histone. Evidence from a pulse-chase experiment with (14C)lysine and[3H]tryptophan is in favour of the cytoplasmic synthesis ofthe histones.  相似文献   

3.
Methenyltetrahydrofolate cyclohydrolase (E.C. 3.5.4.9 [EC] ), whichis responsible for the enzymatic conversion of 5,10-methenyl-H4FAto 10-formyl-H4FA, has been found in various plant tissues.The enzyme was partially purified from pea seedlings and someof its properties were investigated. It was unstable, but wasstabilized by the addition of 25% glycerol. The enzyme was purifiedabout 60-fold by fractionation with ammonium sulfate and columnchromatography on DEAE-cellulose in the presence of 25% glycerol.Optimum pH for the reaction was 7.7. Michaelis constants for5,10-methenyl-H4FA in the forward reaction, and for 10-formyl-H4FAin the reverse reaction were 4x10–5M and 2x10–4M,respectively. The apparent equilibrium constant for the reactionwas calculated as 50. Enzyme activity was greatly inhibitedby the reduced forms of folate derivatives. The probable participationof this enzyme in the regulation of folate coenzyme levels inplant tissues has been suggested. 1 Studies on the enzymatic synthesis and metabolism of folatecoenzymes in plants, VI. (For Part V, see Reference (5) ). Partof this paper was presented at the 22nd annual meeting of theJapan Vitamin Society held at Hiroshima on October 14, 1970. 2 Present address: Sizuoka Eiwa Junior College, Ikeda, Shizuoka. (Received September 9, 1972; )  相似文献   

4.
CLERK  G. C. 《Annals of botany》1972,36(4):801-807
Sporangia of Phytophthora palmivora germinated by either forminggerm tubes or producing zoospores. Two distinct modes of germ-tubedevelopment have been described. Sporangia in distilled waterformed zoospores at 10–34°C with an optimum at 22°Cbut germinated by means of germ tubes at 30 and 34°C only.Zoospore formation was inhibited to varying degrees by cocoapod extract, I.0 per cent (w/v) peptone and yeast extract, 100–500µg1-1 thiamine, and by very low concentrations of severalamino acids, carbohydrates, and inorganic salts. Germ-tube formation was encouraged at 22°C by 1'0 per cent(w/v) peptone and yeast extract, by cocoa pod extract and exudate,10mM CaCl2, 1–10 mM MgSO4. 7H2O, 0.5 per cent (w/v) fructose,galactose, glucose, lactose, maltose, and sucrose, by 100 ppmarginine, aspartic acid, glutarnic acid, glycine, leucine, andtryptophane, and by 100–500 µg 1-1 thiamine.  相似文献   

5.
Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown for 71 d in flowing nutrient solutions containingN as 10 mmol m–3 NH4NO3, under artificial illumination,with shoots at 20/15°C day/night temperatures and root temperaturereduced decrementally from 20 to 5°C. Root temperatureswere then changed to 3, 7, 9, 11, 13, 17 or 25°C, and theacquisition of N by N2 fixation, NH4+ and NO3 uptakewas measured over 14 d. Shoot specific growth rates (d. wt)doubled with increasing temperature between 7 and 17°C,whilst root specific growth rates showed little response; shoot:root ratios increased with root temperature, and over time at11°C. Net uptake of total N per plant (N2 fixation + NH4++ NO3) over 14 d increased three-fold between 3 and 17°C.The proportion contributed by N2 fixation decreased with increasingtemperature from 51% at 5°C to 18% at 25°C. Uptake ofNH4+ as a proportion of NH4+ + NO3 uptake over 14 d variedlittle (55–62%) with root temperature between 3 and 25°C,although it increased with time at most temperatures. Mean ratesof total N uptake per unit shoot f. wt over 14 d changed littlebetween 9 and 25°C, but decreased progressively with temperaturebelow 9°C, due to the decline in the rates of NH4+ and NO3uptake, even though N2 fixation increased. The results suggestthat N2 fixation in the presence of sustained low concentrationsof NH4+ and NO4 is less sensitive to low root temperaturethan are either NH4+ or NO3 uptake systems. White clover, Trifolium repens L. cv. Huia, root temperature, nitrogen fixation, ammonium, nitrate  相似文献   

6.
Acclimation of NO3 transport fluxes (influx, efflux)in roots of oilseed rape (Brassica napus L. cv. Bien venu) andtheir sensitivity to growth at low root temperature was studiedin relation to external NO3 supply, defined by constantconcentrations ranging from sub- to supra-optimal with respectto plant growth rate. Plants were grown from seed in flowingnutrient solutions containing 250 mmol m–3 NO3at 17°C for 20d, and solution temperature in half the cultureunits was then lowered decrementally over 3 d to 7°C. Threedays later plants were supplied with NO3 at 1, 10, 100or 1000 mmol m–3 maintained for 18 d. Dry matter productionwas decreased more by low root zone temperature than low [NO3]e. Root specific growth rates were inversely related to [NO3]eand shoot:root ratios increased with time at [NO3]e between10–1000 mmol m–3. Net uptake of NO3 at 17°Cwas twice that at 7°C, and at both temperatures it doubledwith increasing [NO3]e between 1–10 mmol m–3with further small increases at higher [NO3]e. Mean unitabsorption rates of NO3 between 0–6 d and 6–14d were linearly related (r2 of 0.79–0.99) to log10[NO].Steady-state Q10 (7–17°C) for uptake between 0–6d were 0.91, 1.62, 1.27, and 1.10, respectively, at [NO3]eof 1, 10, 100, and 1000 mmol m–3, compared with correspondingvalues of 0.98, 1.38, 1.68, and 1.89 between 6–14 d. Thedata indicated that net uptake rates at 7 and 17°C divergedover time at high [NO3]e. Short-term uptake rates from1 mol m–3 NO3 measured at 17°C were higherin plants grown with roots at 7°C than at 17°C; for7°C plants there was a strong inverse linear relationship(r2=0.94) between uptake rate and treatment log10 [NO3]ewhilst rates in 17°C plants were independent of prior [NO3]e. Rates of NO3 influx and efflux under different steady-stateconditions of NO3 supply and root temperature were calculatedfrom dilution of 15N added to culture solutions. Efflux wassubstantial relative to net uptake in all treatments, and wasinversely related to [NO3]e at 17°C but not at 7°C.Ratios of influx: efflux ranged from 1.6–2.9 at 17°Cand 1.3–1.8 at 7°C, indicating the proportionatelygreater impact of efflux at low root temperature. Ratios ofefflux: net uptake were 0.53–1.56 at 17°C and 1.21–3.58at 7°C. The apparent sensitivities of influx and effluxto steady-state root temperature varied with [NO3]e.Both fluxes were higher at 17°C than 7°C in the presenceof 100–1000 mmol m–3 NO3 but the trend wasreversed at 1–10 mmol m–3 NO. Concentrations oftotal N measured in xylem exudate were at least 2-fold higherat 7°C compared with 17°C, attributable mainly to higherconcentrations of NO3 glutamine and proline. The resultsare discussed in terms of acclimatory and other responses shownby the NO3 transport system under conditions of limitingNO3 supply and low root temperature. Key words: Brassica napus, nitrate supply, efflux, influx, root temperature, xylem exudate  相似文献   

7.
Mesophyll resistance to photosynthetic carboxylation (r'm) wasused as a criterion for leaf integrity. It was measured, at25 °C, in the light, before and after periods of high temperature(3 h at 38 °C) in the dark. During the high temperatureperiods, respiration (RD) of attached leaves of Xanthium strumariumwas suppressed from 27%-36% by either low [O2] (1.04% or 0.21%v.v.) or high [CO2] (840 µl 1–1) in the ambientair. Neither treatment affected rates of RD or photo-respirationduring the second period at 25 °C. There was no significant increase of r'm when RD was not suppressedduring the high temperature treatment. When RD was suppressedat high temperatures, r'm increased from about 3s cm–1before, to about 26 s cm–1 after the high temperaturetreatment. The increase depended upon the degree of suppression. It is concluded that increased RD at high temperature in Xanthiumleaves is partly the result of an increase of energy demandingmaintenance. The subsequent rate of carbon dioxide fixationis reduced when this increase of maintenance-induced respirationis inhibited.  相似文献   

8.
Single clonal plants of white clover (Trifolium repens L) grownfrom explants in a Perlite rooting medium, and dependent fornitrogen on N2 fixation in root nodules, were grown for severalweeks in controlled environments which provided two regimesof CO2, and temperature 23/18 °C day/night temperaturesat 680 µmol mol–1 CO2, (C680), and 20/15 °Cday/night temperatures at 340 µmol mol–1 CO2 (C340)After 3–4 weeks of growth, when the plants were acclimatedto the environmental regimes, leaf and whole-plant photosynthesisand respiration were measured using conventional infra-red gasanalysis techniques Elevated CO2 and temperature increased ratesof photosynthesis of young, fully expanded leaves at the growthirradiance by 17–29%, despite decreased stomatal conductancesand transpiration rates Water use efficiency (mol CO2 mol H2O–1)was also significantly increased Plants acclimated to elevatedCO2, and temperature exhibited rates of leaf photosynthesisvery similar to those of C340 leaves ‘instantaneously’exposed to the C680 regime However, leaves developed in theC680 regime photosynthesised less rapidly than C340 leaves whenboth were exposed to a normal CO2, and temperature environmentIn measurements where irradiance was varied, the enhancementof photosynthesis in elevated CO2 at 23 °C increased graduallyfrom approx 10 % at 100 µmol m–1 s–1 to >27 % at 1170 µmol m–2 s–1 In parallel, wateruse efficiency increased by 20–40 % at 315 µmolm–2 s–1 In parallel, water use efficiency increasedby 20–40 % at 315 µmol m–2 s–1 In parallel,water use efficiency increased by 20–40 % at 315 µmolm–2 s–1 In parallel, water use efficiency increasedby 20–40 % at 315 µmol m–2 s–1 to approx100 % at the highest irradiance Elevated CO2, and temperatureincreased whole-plant photosynthesis by > 40 %, when expressedin terms of shoot surface area or shoot weight No effects ofelevated CO2 and temperature on rate of tissue respiration,either during growth or measurement, were established for singleleaves or for whole plants Dependence on N2, fixation in rootnodules appeared to have no detrimental effect on photosyntheticperformance in elevated CO2, and temperature Trifolium repens, white clover, photosynthesis, respiration, elevated CO2, elevated temperature, water use efficiency, N2 fixation  相似文献   

9.
Bergersen  F. J. 《Annals of botany》1993,72(6):577-582
The diffusion of oxyleghaemoglobin, prepared from soybean rootnodules, was measured at 24°C in agar and agarose gels ofvarious strengths, or in 1% agarose containing 0-18% (w/v) bovineserum albumin, to simulate the protein content of the cytoplasmof root nodule cells. Values of Dp, the diffusion coefficient,were unaffected (Dp = 11·8 x 10-11 m2 s-1; s.e.m. 0·3x 10-11) until the protein concentration exceeded 6%, abovewhich Dp declined sharply. With 18% bovine serum albumin, theconcentration of total soluble protein calculated to be presentin the cytoplasm of infected cells, where most of the leghaemoglobinis located in vivo, Dp was 5·9 x 10-11 m2 s-1. Theseresults are discussed in relation to leghaemoglobin-facilitateddelivery of O2 to the respiring N2-fixing bacteroids in rootnodule cells.Copyright 1993, 1999 Academic Press Bacteroids, diffusion, Glycine max, N2 fixation, oxyleghaemoglobin, soybean, root nodules  相似文献   

10.
The rates of photosynthetic 14CO2 fixation by Chlorella vulgarisllh, grown under high CO2, were determined between 4 to 37°Cwith air containing from 300 to 13,000 ppm 14CO2. When the CO2level was increased, both the rate of photosynthesis and theoptimum temperature for maximum photosynthesis increased. Themaximum photosynthetic rate was reached at 12°C with 300ppm l4CO2. Among the photosynthetic products fromed at 300 ppm 14CO2, glycolatedecreased greatly when the temperature was raised from 20 to30°C. At 3,000 ppm 14CO2 an insignificant amount of glycolatewas formed at all temperatures, whereas 14C-incorporation intothe insoluble fraction, sucrose, and the lipid fraction wassignificantly higher than at 300 ppm 14CO2. The 14C in sucrosewas greatly increased and the radioactivity in the insolublefraction decreased when the temperature was raised from 28 to36°C. (Received April 8, 1980; )  相似文献   

11.
Dark fixation of 14CO2 was followed in potato disks under varyingsalt treatments at 0° C and 25° C. It is shown thatthe specific activity of the 14CO2 supplied is heavily dilutedby endogenously produced CO2 and that the apparently greaterfixation of 14CO2, at 0° C as compared with that at 25 °C is due to the lower respiration rate at 0° C, with consequentlyless dilution of the 14CO2. supplied. At 25° C organic acidformation in response to different salt treatments fulfils thecommon expectation, 14CO2 fixation increasing in the presenceof K2SO4 and decreasing in CaCl2 relative to that in KCl. Therole of organic acids in maintaining ionic balance within thecell at 25° C is thereby indicated but at 0° C organicacid adjustments did not follow the normal pattern. At 25°C but not at o° C increasing external concentration of KCIresulted in an increased level of 14CO2 fixation.  相似文献   

12.
A stable freeze-dried powder was prepared of partly purifiedribulose bisphosphate carboxylase from wheat leaves. As withpreparations from other leaves it is necessary to incubate theenzyme with Mg2$ and CO2 to achieve maximum activity. At 25°C this activity was 0.75 IU mg–1 protein for a preparationactivated at 50 °C for 10 min; the Km for CO2 was 15 µM. The time for reactivation of enzyme that had been inactivatedthrough the absence of CO2 and Mg2$ was influenced by the lengthof the inactivating treatment. After a short inactivation periodthe enzyme was reactivated within a few minutes, whereas aftera longer period several hours were needed. Enzyme in the latterstate had some properties in common with enzyme inactivatedby lower temperatures but in the presence of CO2 and Mg2$. Theenzyme kinetic characteristics are similarly affected by bothkinds of inactivation; the maximum velocity is decreased butthe affinity for CO2 is not affected. Reactivation following a long inactivating treatment becomesmore dependent on Mg2$ concentration as the temperature is increasedfrom 0 to 20 °C.  相似文献   

13.
The enzyme N-acetylglucosamine-1-phosphodiester -N-acetylglucosaminidase(EC 3.1.4.45 [EC] ; uncovering enzyme) catalyzes the removal of N-acetylglucosaminefrom the N-acetylglucosamine--phospho-mannose portion of selectedlysosomal enzyme oligosaccharide chains, thereby formimg themannose 6-phosphate signal which is responsible for the targetingof these lysosomal enzymes for transport into lysosomes. Theuncovering enzyme has been purified approximately 7000-foldto electrophoretic homogeneity from Epstein-Barr virus-transformedhuman lymphoblast cells. The purification sequence involvessolubilizing this membrane-bound enzyme with Tergitol NP-10,affinity chromatography on Lentil lectin-Sepharose 4B, ion-exchangechromatography on DEAE-Sephacel, chromatography on zinc(II)-IDA-Sepharose6B, and preparative SDS-PAGE electrophoresis. The purified enzymemigrated as a single band of 114 kDa which was coincident withenzyme activity on analytical SDS-PAGE electrophoresis. Characterizationstudies of the purified enzyme demonstrated that catalytic activitywas maximal at pH 6.95 and that the enzyme retained full activityfollowing incubation for 10 min at 60°C. No requirementwas found for a divalent cation, but Zn2+ Hg2+ and Cu2+ werefound to reduce the enzyme's activity by 30–40%. The highestcatalytic efficiency was observed with N-acetylglucosamine phospho-methylmannosideas a substrate while uridine diphosphate-N-acetylglucosamine,N-acetylglucosamine phosphomannose-uteroferrin, and N-acetylglucosaminephosphate were also cleaved by the enzyme with decreasing efficiency.Acetamino-deoxycastanospermine was a potent inhibitor of thehuman enzyme with a K1 of 0.35 µM, while N-acetylglucosaminephosphate (K1 1.58 mM) and N-acetylglucosamine (K1 5.1 mM) inhibitedthe enzyme to a lesser degree. N-acetylglucosamine-1-phosphodiester -N acetylglucosaminidase lymphoid cells targeting mannose-6 phosphate  相似文献   

14.
The effect of high light and root chilling on gas exchange,chlorophyll fluorescence, and bulk shoot water potential (shoot)was examined for Pinus sylvestris seedlings. Transferring plantsfrom low light (200 µmol m–2s–1, PAR) anda soil temperature of 15 °C to high light (850 µmolm–2 s–1) and 1 °C caused >90% decrease innet photosynthesis and leaf conductance measured at 350 mm3dm-3 CO2, and a decrease in the ratio of variable to maximumfluorescence (Fv/Fm) from 0.83 to 0.63. The decrease in Fv/Fmwas, however, only marginally greater than when seedlings weretransferred from low to high light but kept at a soil temperatureof 15 °C. Thus, photoinhibition was a minor component ofthe substantial decrease observed for net photosynthesis at1 °C soil temperature. The decrease in net photosynthesisand shoot at 1 °C was associated with an increase in calculatedintracellular CO2 concentration, suggesting that non-stomatalfactors related to water stress were involved in inhibitingcarbon assimilation. Measurements at saturating external CO2concentration, however, indicate that stomatal closure was thedominant factor limiting net photosynthesis at low soil temperature.This interpretation was confirmed with additional experimentsusing Pinus taeda and Picea engelmannii seedlings. Decreasesin gas-exchange variables at 5 °C soil temperature werenot associated with changes in shoot Thus, hormonal factors,localized decreases in needles or changes in xylem flux maymediate the response to moderate root chilling.  相似文献   

15.
The relationship between germination and PFR level in sporesof the fern Lygodium japonicum was investigated. Percent PFRestimated from direct spectrophotometric measurement of sporesincreased with the logarithm of total fluence of 660 nm-light.The transformation from PR to PFR was saturated by giving ca.200 Jm–2 of 660 nm-light and half-saturated by ca. 55J–2 of 660 nm-light. Clear positive correlation was observedbetween % PFR levels and germination rates in spores irradiatedwith 660 nm and/or 730 nm-light, or with 686 or 700 nm-light.The PFR percentage in spores was raised to 16–34% by blue(415 nm) light irradiation. This PFR level was enough to causesome germination when produced by monochromatic light of redto far-red region, but blue light did not cause any germination. After 660 nm-light irradiation, the PFR level decreased graduallyin darkness (25±1°C) and PFR completely disappearedin 8 h, but 730 nm-light given even 16 h after 660 nm-lightirradiation inhibited germination. 4Present address: Tropical Botanic Garden and Research Institute,Navaranga Road, Trivandrum 695 011, India. (Received March 15, 1983; Accepted June 4, 1983)  相似文献   

16.
The effect of carbonic anhydrase (CA) on time courses of photosynthetic14C incorporation in the presence of 14CO2 or NaH14CO3 was studiedwith cells of Chlamydomonas reinhardtii which had been grownunder ordinary air (low-CO2 cells) or air enriched with 4% CO2(high-CO2 cells). Experimental data obtained at 20°C andpH 8.0 suggested that the major form of inorganic carbon utilizedby high-CO2 cells was CO2, while that utilized by low-CO2 cellswas HCO3. The cell suspension showed CA activity which was comparableto that observed in the sonicate of cells. Both activities werehigher in low-CO2 cells than in high-CO2 cells. The mechanism by which HCO3 is utilized by low-CO2 cellsof C. reinhardtii is discussed. 3Present address: Department of Biology, Faculty of Science,University of Niigata, Niigata 950-21, Japan. (Received August 4, 1982; Accepted January 19, 1983)  相似文献   

17.
Murata  Takao 《Plant & cell physiology》1976,17(6):1099-1109
Phosphomannomutase [Glazer et al.: Biochim. Biophys. Acta 33:522–625 (1959)] was purified 1700-fold in a 39% yieldfrom cell-free extract of konjak (Amorphophallus konjac C. Koch)corms. The molecular weight of the enzyme as determined by gelfiltration was about 62,000. The enzyme required both Mg2+ and-D-glucose-l,6-bisphosphate for activity, although Mg2+ waspartially replaceable by either Co2+ or Ni2+. An apparent equilibriumconstant, Keq=(mannose-6-phosphate) (mannose-1-phosphate), wasdetermined to be 8.5. Activity was maximal at pH 6.5 to 7.0.Activation energy was 11.1 kcal/mole. The enzyme was the moststable at pH 7.5. The addition of substrate or cofactor markedlyincreased enzyme stability toward heat denaturation. The enzymewas more labile to heat than phosphoglucomutase from konjakcorms. Treatment with various metal ions in Tris buffer inhibited theenzyme. Cu2+ and Zn2+ were the most potent inhibitors amongthe metal ions tested, while Co2+ and Ni2+ were weak. When theenzyme was treated with metal ions in the presence of histidinebuffer, Cu2+ and Zn2+ showed no inhibitory effect on the enzyme,whereas Be2+ inhibited it to an extent similar to that in Trisbuffer. Plots of 1/v versus l/(mannose-l-phosphate) at different fixedconcentrations of glucose-1,6-bisphosphate and 1/v versus 1/(glucose-1,6-bisphosphate)at different fixed concentrations of mannose-1-phosphate wereseries of converging lines. Mannose-1-phosphate at high concentrationswas found to inhibit the enzyme competitively with respect toglucose-l,6-bisphosphate. Apparent Km and K1 values for mannose-1-phosphatewere calculated to be 0.2 mM and 1.2 mM, respectively. The Kmvalue for glucose-1,6-bisphosphate was 1.8 µM. 1This paper constitutes part 5 of a series of studies on konjakmannan biosynthesis. (Received May 24, 1976; )  相似文献   

18.
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   

19.
Chloroplast preparations from the young primary leaves of Phaseolusvulgaris L. cv. Canadian Wonder carry out the DNA-dependentincorporation of UTP into RNA at rates between 8 and 14 pmolUTP µg–1 chlorophyll h–1. It is estimatedthat 90% of the activity was localized in the chloroplasts.The incorporation proceeded for between 20 and 30 min at 35°C. The maximum rates of RNA synthesis were attained atpH 8.3, in the presence of 15 mM MgCl2. Chloroplasts were alsoactive, to a lesser extent, with 1.5 mM MnCl2. The simultaneouspresence of MnCl2 and MgCl2 resulted in inhibition of activity.Nuclear material prepared from young P. vulgaris leaves incorporatedUTP at a rate of about 12 pmol UTP µg–1 DNA h–1.On a chloroplast (Tritonsoluble) DNA basis chloroplast activitywas over 40-fold that of nuclei. Methods of solubilizing chloroplastRNA polymerase were explored. Yields of over 75% were achieved,but methods suitable for one species were not always successfulwhen applied to another. The highest yields of the P. vulgarisenzyme were obtained using EDTA and KCl. All methods resultedin solubilization of DNA. RNA synthesis by the soluble P. vulgarisenzyme proceeded for more than 40 min at 35 °C.  相似文献   

20.
Elevated levels of Pi are thought to cause a substantial proportion of the loss in muscular force and power output during fatigue from intense contractile activity. However, support for this hypothesis is based, in part, on data from skinned single fibers obtained at low temperatures (15°C). The effect of high (30 mM) Pi concentration on the contractile function of chemically skinned single fibers was examined at both low (15°C) and high (30°C) temperatures using fibers isolated from rat soleus (type I fibers) and gastrocnemius (type II fibers) muscles. Elevating Pi from 0 to 30 mM at saturating free Ca2+ levels depressed maximum isometric force (Po) by 54% at 15°C and by 19% at 30°C (P < 0.05; significant interaction) in type I fibers. Similarly, the Po of type II fibers was significantly more sensitive to high levels of Pi at the lower (50% decrease) vs. higher temperature (5% decrease). The maximal shortening velocity of both type I and type II fibers was not significantly affected by elevated Pi at either temperature. However, peak fiber power was depressed by 49% at 15°C but by only 16% at 30°C in type I fibers. Similarly, in type II fibers, peak power was depressed by 40 and 18% at 15 and 30°C, respectively. These data suggest that near physiological temperatures and at saturating levels of intracellular Ca2+, elevated levels of Pi contribute less to fatigue than might be inferred from data obtained at lower temperatures. skinned single fiber; force; power  相似文献   

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