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1.
Inhibition of nitrate reductase from spinach (Spinacea oleracea L.) leaf by adenosine nucleotides 总被引:1,自引:0,他引:1
NADH-dependent nitrate reductase of spinach showed ping-pongKinetics. Inhibition by ADP in the absence of thiols increasedduring a transient phase during which Kinetics changed fromweak (K1 20 mM), non-competitive and linear to comparativelystrong (K1 0.09 mM at 10 mM ADP), mixed with respect to NADHand non-linear (nH = 1.7). Thiol compounds transformed the inhibitionto competitive (K1 0.18 mM at 10 mM ADP) and non-linear (nH= 2.3). Effective concentrations increased in order: GSH>mercaptoethanol= thioglycollate>cysteine, and were increased by dissolvedoxygen or disulphide. Non-competitive inhibition by ribose-5-phosphate(K1 3 nua) was abolished by glutathione. Cyclic 3',5'-AMP inhibitednon-linearly (nH=2.4) and comparably to or more than ADP (K10.22 mM at 2.5 mM) but predominantly competitively except atlow NADH concentrations. Cyclic 2',3'-AMP showed similar butweaker inhibition (K1 1.4 mM) and more nearly linear (nH =1.3).5'-AMP inhibited competitively (K1 1.2 mM at 10 mM) (nH = 1.3).5'-ATP showed weak mixed inhibition (K1 5 nun at 10 mM) (nH= l.3). Activity with BV° was scarcely inhibited by ADP,but phosphate activation with BV° or NADH were both inhibitedby ADP. Physiological significance of inhibition by ADP is discussedand might lie between 3% in light and 25% in dark in specialcircumstances of thiol supply.
1 Present address: Department of Soil Microbiology, RothamstedExperimental Station, Harpenden, Herts. (Received May 22, 1975; ) 相似文献
2.
《Environmental and Experimental Botany》2007,59(1):43-48
Acid phosphatases (E.C.3.1.3.2) are a group of enzymes widely distributed in nature, which nonspecifically catalyze the hydrolysis of a variety of phosphate esters in pH ranges from 4 to 6 and play a major role in the supply and metabolism of phosphate in plants. The objective of the present study was to investigate the in vitro effects of some metals on the activity of acid phosphatase in cucumber seedlings (Cucumis sativus L.) and to determine their kinetic parameters. The enzyme was assayed with Hg, Cd, Mn, Pb, Zn, K and Na at the 0.001–1 mM range using ATP, PPi and β-glycerol phosphate as substrates. Mn, Na and Cd did not significantly alter the enzyme activity. K caused a broad activation at low concentrations and an inhibition at high concentrations (10 mM) and lead caused no inhibition. Acid phosphatase was inhibited by Hg and Zn and the inhibition type and IC50 values were determined for these metals. Hg presented a mixed inhibition type with PPi and ATP as substrates and uncompetitive inhibition with β-glycerol phosphate as substrate. Zn presented competitive inhibition for ATP as substrate, and a mixed inhibition type with PPi and β-glycerol phosphate as substrate. IC50 values were 0.02, 0.3 and 0.15 mM for Hg, and 0.056, 0.035 and 0.24 mM for Zn with ATP, PPi and β-glycerol phosphate as substrates, respectively. Analysis of these results indicates that Zn is a more potent inhibitor of acid phosphatase from cucumbers than Hg. 相似文献
3.
Summary
Salicornia fruticosa was collected from a salt marsh on the Mediterranean sea coast in Libya. Growth and gas exchange of this C3 species were monitered in plants pretreated at various NaCl concentrations (0, 171, 342, 513 and 855 mM). Maximum growth was at 171 mM NaCl under cool growth conditions (20/10° C) and at 342 mM NaCl under warm growth conditions (30/15° C) with minimum growth at 0 mM NaCl (control). Net photosynthesis (Pn) was greatest in plants grown in 171 mM NaCl with plants grown at 513 and 855 mM having lowest rates. Maximum Pn was at 20–25° C shoot temperatures with statistically significant reductions at 30° C in control plants while salt treated plants showed such reductions at 35° C. Salt treatments increased dark respiration over the control at 171 and 342 mM but reduced it at higher concentrations. Photorespiration was reduced by salt treatment and increased by increasing shoot temperature. Greatest transpiration was in 171 mM NaCl treated plants and increasing shoot temperature increased transpiration in all treatments. Stomatal resistance to CO2 influx was influenced only moderately by temperature while increasing salinity resulted in increased stomatal resistance. In general both temperature and salinity increased the mesophyll resistance to CO2 influx. The species seems adapted to the warm saline habitat along the Mediterranean sea coast, at least partially, by its ability to maintain relatively high Pn at moderate NaCl concentrations over a broad range of shoot temperatures. 相似文献
4.
A procedure is described which allows the purification of fructokinase (EC 2.7.1.4) from young tomato fruit. The procedure yielded a 400-fold purification and two isoenzymes designated fructokinase I and II (FKI and FKII) were separated by anion-exchange chromatography. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) the molecular mass was estimated to be 35 kDa. Gel filtration on Sepharose-12 indicated that for both fructokinases the functional form is a dimer. Two dimensional isoelectric focusing/SDS-PAGE combined with immunoblotting showed that FKI has two components with isoelectric points (pIs) of 6.42 and 6.55, while four components with pIs from 6.07 to 6.55 were detected for FKII. A mixture of both fructokinases showed that the components of FKI match the more alkaline components of FKII. The activity of both fructokinases increased with increasing pH to around 8.0 and equal activity was observed from 8.0 to 9.5. Both fructokinases were specific for fructose with K m values for fructose of 0.131 and 0.201 mM for FKI and FKII, respectively. At high concentrations (> 0.5 mM), fructose was also a strong inhibitor with inhibition constants (K i) of 1.82 and 1.39 mM for FKI and FKII, respectively. The preferred phosphate donor for both isoforms was ATP, and K m values of 0.11 and 0.15 mM were observed for FKI and FKII. At low concentrations (0.05–0.2 mM), fructose exhibited noncompetitive inhibition with respect to ATP for both fructokinases. This inhibition pattern changed to uncompetitive when higher fructose concentrations (0.5–10 mM) were used. These data indicated that substrate addition is ordered, with ATP adding first. Inhibition by ADP was also affected by the fructose concentrations. At 0.5 mM fructose, FKI showed non-competitive inhibition by ADP with respect to ATP and this inhibition changed to uncompetitive when 3 mM fructose was used. The isoform FKII showed a competitive inhibition pattern for ADP at 0.5 mM fructose which also changed to uncompetitive when 3 mM fructose was used. The features of the regulation of both fructokinases suggest that this enzyme might have a relevant role in carbon metabolism during tomato fruit development. 相似文献
5.
Jolanta Jerzykiewicz 《Acta Physiologiae Plantarum》2001,23(2):213-219
In vivo effect of aluminium on nitrate uptake and reduction by cucumber seedlings was investigated. The high-performance liquid chromatography
was used to analyse the rate of nitrate uptake. Low (0.5 mM) concentration of AlCl3 in the nutrient solution stimulated nitrate uptake during the first 3 h. On the other hand, 6 h exposure of the cucumber
seedlings to 1 or 5 mM of AlCl3 resulted in inhibition of nitrate uptake and at 5 mM concentration of AlCl3 the efflux of nitrate was observed. Furthermore, the amount of nitrate accumulated in cucumber roots after aluminium treatment
was decreased. The noteworthy fact was observed, that at all concentrations of aluminium tested on increase of the nitrate
reductase activity. This stimulation was concentration depended, but independent of the source of the enzyme. The activity
of both the cytosolic and the plasma membrane bound nitrate reductase activity was enhanced in vivo. On the other hand, AlCl3 applied in vitro only slighty decreased nitrate reductase activity. 相似文献
6.
J. M. Holmes A.-S. Gräns D. M. Neil S. P. Baden 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(6):402-410
The effects of the metal ions manganese and cobalt on force production by the abdominal superficial flexor muscle of the
Norway lobster, Nephrops norvegicus, have been studied in response to both neuronal stimulation and electrical field stimulation applied to an isolated neuromuscular
preparation, and by selectively blocking synaptic transmission with ivermectin. In response to both forms of stimulation,
low concentrations of manganese added to the standard N. norvegicus saline increased the contractile force produced by the muscle, whereas higher concentrations of manganese inhibited both
responses in a dose-dependent manner, until force was completely abolished at concentrations above 2.9 mM manganese. Cobalt
ions produced similar effects, and no significant difference was found between the concentration of the two ions at 50% force
inhibition (Km) or between the two stimulation methods (manganese: 1.22 mM; cobalt: 1.29 mM, P = 0.86). This suggests that they have a similar mode of action, and a postsynaptic site of inhibition. These Km values are considerably higher than the concentrations of these ions known to accumulate in the haemolymph of N.
norvegicus under eutrophic conditions, and it therefore seems unlikely that accumulations of manganese or cobalt ions under such conditions
would cause any significant inhibition of muscle contraction force.
Accepted: 28 April 1999 相似文献
7.
Schulte AE van der Heijden R Verpoorte R 《Archives of biochemistry and biophysics》2000,378(2):287-298
Mevalonate kinase was purified to homogeneity from Catharanthus roseus (L.) G. Don suspension-cultured cells. The purified enzyme had an M(r) of 104,600 and a subunit size of about 41,500. Kinetic studies indicated an ordered sequential mechanism of action, in which mevalonate was the first substrate to bind and ADP was the last product to leave the enzyme. True values for the kinetic constants were determined for mevalonate, with K(ma) = 76 microM and K(ia) = 74 microM, and for ATP, with K(mb) = 0.13 mM and K(ib) = 0. 13 mM; the true V(max) was calculated to be 138.7 nkat/mg of protein. Product inhibition was only detectable at rather high concentrations: above 0.7 mM for 5-phosphomevalonate and above 2 mM for ADP, with an ADP/ATP ratio of at least 1. Mevalonate kinase activity was shown to be strongly inhibited by farnesyl diphosphate. Farnesyl diphosphate acted as a competitive inhibitor toward ATP, with a K(i) value of 0.1 microM. Mevalonate kinase activity was dependent on the presence of divalent ions. At a concentration of 2 mM, Mg(2+) and Mn(2+) were best and equally effective in sustaining activity; compared to Mg(2+) and Mn(2+), relative activities of 35, 30, 16, 4.8, and 3.4% were detected at equimolar concentrations of Zn(2+), Fe(2+), Co(2+), Ca(2+), and Ni(2+), respectively. The pH-dependent activity profile of mevalonate kinase showed a broad pH optimum between pH 7 and 10, with a maximum at about pH 8.9. 相似文献
8.
The tolerance of nickel by Frankia in culture and in symbiosis with Alnus was determined. Yield of three Frankia strains was not affected significantly by 2.25 mM nickel when cultured in propionate medium containing hydolysed casein as nitrogen source. Yield of two strains in medium without combined nitrogen, and thus reliant on fixed nitrogen, was stimulated markedly by the same nickel concentration. Utilisation of nickel for synthesis of uptake hydrogenases is presumed to be the cause of enhanced nitrogenase activity.Although growth was reduced, treatment of 2-month-old seedlings with 0.025 mM nickel for 4 weeks did not affect nodulation significantly while nitrogenase activity was doubled. Nodulation and nitrogenase activity of seedlings receiving 0.075 mM nickel were inhibited markedly, while 0.5 mM nickel was lethal to all seedlings after 4 weeks of treatment. A few small, ineffective nodules were initiated early on some of the latter seedlings, suggesting that effects of nickel on host plant processes rather than Frankia are the primary cause of inhibition of nodulation. This interpretation is supported by the retention of substantial nitrogenase activity in 10-month-old plants 1 day after the treatment with 0.59 mM nickel, when the nickel content of roots and nodules was already maximal. No nitrogenase activity was detected after 3 days, by which time the leaves were almost completely necrotic. Over a 4 day period, most nickel was retained in the roots and nodules. Supplying histidine simultaneously at concentrations equal to, or in excess of, nickel prevented wilting and leaf necrosis, but did not increase translocation of nickel to the shoot. 相似文献
9.
In intact soybean roots, chlorpromazine causes a depolarization of the membrane potential at low concentrations (as low as 30 μM, half-maximally at about 150 μM), and induces a marked decrease in ATP levels at higher concentrations (half-maximal at about 0.5 mM) over longer periods of time. In root microsomal suspensions, chlorpromazine inhibits an apparently specific ATPase activity component (half-maximally at about 0.3 mM). Chlorpromazine inhibits -, diethylstilbesterol- and azide-inhibited ATPase activities. On linear sucrose gradients, chlorpromazine inhibition of ATPase activity occurs in two peaks, at 1.12 g/ml and 1.14–1.17 g/ml, which may represent a tonoplast and plasma membrane ATPase, respectively. Neither peak corresponds to the F1 ATPase. It is unclear whether ATPase inhibition or ATP loss is the cause of the membrane potential depolarization. Clearly chlorpromazine has multiple effects which are probably unrelated to its calmodulin-inhibition activity. 相似文献
10.
Dr. Bruce I. Reisch Stanley H. Duke E. T. Bingham 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1981,59(2):89-94
Summary Diploid alfalfa (HG2), capable of plant regeneration from tissue culture, was used to select variant cell lines resistant to growth inhibition due to ethionine (an analog of methionine). Approximately 107 suspension-cultured cells were mutagenized with methane sulfonic acid ethylester and then plated in solid media containing ethionine. Callus colonies formed on media with 0.02 mM ethionine. Of the 124 cell lines recovered, 91 regenerated plants. After six months growth on media without ethionine, 15 of 110 cell lines of callus grew significantly better than HG2 on 1 mM ethionine. Several ethionine-resistant callus cultures were also resistant to growth inhibition due to the addition of lysine + threonine to the media. High concentrations, relative to unselected HG2 callus, of methionine, cysteine, cystathionine, and glutathione were found in some, but not all, ethionine-resistant callus cultures. Cell line R32, which had a ca. tenfold increase in soluble methionine, had a 43% increase in total free amino acids and a 40% increase in amino acids in protein as compared to unselected HG2 callus. Relative amounts of each amino acid in protein were the same in both.Abbreviation LT
lysine + threonine in equimolar concentration 相似文献
11.
In order to clearly establish the properties of the enzymes responsible for hexose phosphorylation we have undertaken the
separation and characterization of these enzymes present in tomato fruit (Martinez-Barajas and Randall 1996). This report
describes the partial purification and characterization of glucokinase (EC. 2.7.1.1) from young green tomato fruit. The procedure
yielded a 360-fold enrichment of glucokinase. Tomato fruit glucokinase is a monomer with a molecular mass of 53 kDa. Glucokinase
activity was optimal between pH 7.5 and 8.5, preferred ATP as the phosphate donor (K
m = 0.223 mM) and exhibited low activity with GTP or UTP. The tomato fruit glucokinase showed highest affinity for glucose
(K
m = 65 μM). Activity observed with glucose was 4-fold greater than with mannose and 50-fold greater than with fructose. The tomato
fruit glucokinase was sensitive to product inhibition by ADP (K
i = 36 μM). Little inhibition was observed with glucose 6-phosphate (up to 15 mM) at pH 8.0; however, at pH 7.0 glucokinase
activity was inhibited 30–50% by physiological concentrations of glucose 6-phosphate.
Received: 4 October 1997 / Accepted: 10 January 1998 相似文献
12.
Edelmann Hans G.; Bergfeld Rainer; Schopfer Peter 《Journal of experimental botany》1995,46(11):1745-1752
The dependence of auxin (IAA)-induced elongation growth on proteinglycosylation was investigated in abraded maize (Zea mays L.)coleoptile segments, employing 2-deoxy-D-glucose (DOG) and tunicamycin(TUM) as inhibitors of protein glycosylation. TUM had no detectableeffect on growth at 100µg ml1. DOG impaired growthat concentrations larger than 1 mM. Total inhibition of growthoccurred at a concentration of 20 mM. Similar effects were observedwith mannose and glucosamine. The effect on wall-synthetic processesin the growth-limiting epidermis was analysed by tracer incorporationstudies. Within 30 min hemicellulose and cellulose synthesis,measured as 3H-glucose incorporation, was not affected by DOG,indicating that inhibition of growth is not causally relatedto synthesis of both wall components. In contrast, protein synthesisand secretion into the walls, measured as incorporation of 3H-leucineinto the TCA-precipitable protoplasmic and wall-bound protein,was rapidly inhibited by DOG. Concomitant with the effect ongrowth, DOG as well as mannose inhibited the occurrence of osmiophilicparticles (OPs) which specifically occur at the growth-limitingepidermis during IAA-induced growth. The results provide evidencethat IAA-induced wall loosening underlying elongation growthis dependent on O-glycosylation of proteins and their subsequentsecretion into the epidermal walls. It appears that interferencewith these processes is responsible for inhibition of IAA inducedgrowth by hexoses acting as anti-glucose antimetabolites. Key words: Auxin-induced growth, cell-wall synthesis, 2-deoxy-D-glucose, mannose, osmiophilic particles, tunicamycin 相似文献
13.
The effect of different types and concentrations of dormancy regulating chemicals (DRCs) on innate and induced dormancy was evaluated under optimal germination conditions in the invasive Prosopis juliflora shrub. Lower concentrations of gibberellic acid (0.3 mM) and kinetin (0.05 mM) were more effective in enhancing germination % and rate at higher concentrations of NaCl, but the reverse was true for thiourea. None of the DRCs alleviated innate dormancy of P. juliflora. Germination % and rate decreased as salinity increased. Percent final germination of non-treated seeds was significantly reduced at 500 mM NaCl and virtually inhibited in 600 mM NaCl. Germination reduction in 500 mM NaCl was not alleviated by any of the DRCs, but inhibition induced at 600 mM NaCl was partially alleviated by all the DRCs. Gibberellic acid had a significantly greater effect than kinetin in alleviating germination inhibition. For restoration of saline soil through the use of P. juliflora, results suggest using DRCs, particularly gibberellic acid and thiourea, as a preseeding treatment can overcome the problem of reduced germination. 相似文献
14.
YEO A. R.; LEE {lambda}.-S.; IZARD P.; BOURSIER P. J.; FLOWERS T. J. 《Journal of experimental botany》1991,42(7):881-889
Addition of 50 mM NaCl to Oryza sativa L. had little effectupon the time of leaf initiation, but leaf mortality prior tothe normal phase of senescence was increased and the onset ofsenescence was advanced. There was no significant effect uponthe day-to-day pattern of growth, nor upon the ultimate length,of leaves that were developing at the time of, or shortly after,salinization with 50 mM NaCI. Leaves that developed after prolongedexposure of the plants to salinity were shorter. Addition ofNaCl, KC1 or mannitol to the root medium brought about a cessationof leaf elongation within one minute. Growth at a reduced raterestarted abruptly after a lag period that depended upon theexternal concentration. Elongation rate recovered its originalvalue within 24 h after exposure to 50 mM NaCl, though not athigher concentrations. Addition of NaCl at concentrations upto 100 mM elicited no short-term effects upon photosyntheticgas exchange. Na uptake contributed to osmotic adjustment ofthe growing zone. When plants were rapidly exposed to 50 mMNaCl, no change in turgor pressure was detectable in the growingzone with the resolution of the miniature pressure probe used(about 70 kPa). It is concluded that the initial growth reductionin rice caused by salinization is due to a limitation of watersupply. A clear distinction is made between the initial effectsof low salinity which are recoverable and the long-term effectswhich result from the accumulation of salt within expanded leaves. Key words: Leaf elongation, gas exchange, photosynthesis, water relations 相似文献
15.
Plant growth and seed yield of mung bean were studied in sand culture at different levels of NaCl [0, 50, 100, 150, 200, 250
mM] in the root medium. Results showed that both dry matter yield and seed yield of plants grown for 14 weeks at 50 mM NaCl
and 100 mM NaCl were around 60 % and 25 %, respectively of those for plants grown in control solution. Higher concentrations
caused wilting and necrosis of leaves. Very effective exclusion of Na and Cl from salt grown mung bean seed was observed with
concommitant high accumulation of Na and Cl in the stem. It is speculated that mung bean plant stem may act as a ‘sink’ for
NaCl during the reproductive stage of the plant growth cycle. 相似文献
16.
S P Schmidt R C Essenberg J R Sauer 《Comparative biochemistry and physiology. C: Comparative pharmacology》1982,72(1):9-14
1. Enzyme activity, basal or dopamine-stimulated (10 microM), was linear with time to 25 min and with protein concentration to 0.8 mg protein/ml of final assay volume. Activity was maximal between pH 7.0 and 7.5. 2. Mg2+ maximally stimulated basal or dopamine-sensitive adenylate cyclase activity at about 4 mM. 3. Adenylate cyclase had a Km of 0.042 mM for ATP and maximum velocities for basal and dopamine-stimulated activity of 107 and 179 pmol cyclic AMP formed/mg protein per min, respectively. 4. Half-maximal stimulation of the enzyme occurred at about 4.2 x 10(-7) M dopamine with the threshold being less than 10(-9) M. Dopamine increased the Vmax but had no effect on the Km of ATP. 5. Eighty-five to 90% of the adenylate cyclase activity was found in the particulate fraction. 6. Calcium ion produced a marked inhibition of adenylate cyclase activity above 0.04 mM and half-maximal inhibition occurred near 0.1-0.2 mM. 相似文献
17.
ROHRINGER ROLAND; EBRAHIM-NESBAT FIROUS; WOLF GERHARD 《Journal of experimental botany》1983,34(12):1589-1605
Primary leaves of barley were detached, infiltrated with variousbuffers, and centrifuged to yield intercellular washingfluid (IWF). Effective pH control of the IWF was obtainedonly with Tris, among all buffers tried. In these liquids, upto 30 proteins were detected by gradient gel electrophoresis.Intracellular protein from injured cells at the cut ends ofleaves was present in IWF but did not contribute significantlyto the total protein recovered in this liquid. The yield ofprotein in the IWF depended on the buffer used for infiltrationand on the concentration of the buffer. Higher concentrationsof buffer yielded more protein. In other experiments leaves were infiltrated with Tris, centrifuged,and then infiltrated a second time with this buffer containingvarious concentrations of the zwitterionic detergent CHAPS,a sulphobetaine derivative of cholate. Gel electrophoresis ofthe IWF obtained after the second centrifugation revealed proteinbands not detected when the detergent had beenomitted from the infiltration buffer. The electrophoretic patternsof protein bands in the gels differed dependingon the CHAPS concentration used for infiltration. The effect of CHAPS on plasmalemma integrity was studied byobserving infiltrated tissue with the electron microscope andby treating isolated protoplasts with the detergent. After infiltrationwith CHAPS at 0.6 mM or 2.0 mM no plasmalemma breaks were detectedin leaves, and isolated protoplasts survived exposure to CHAPSat these concentrations for 2 h without bursting. Evidently,CHAPS at these low concentrations did not destroy the integrityof the plasmalemma; the additional protein recovered in theIWF under these conditions probably originated in the cell wall.Infiltration of leaves with 6.0 mM CHAPS resulted in breaksof the plasmalemma, in tissue collapse and leaf tip necrosis.Isolated protoplasts burst within minutes after being exposedto CHAPS at this concentration. Key words: Cell wall permeability, Intercellular space, Detergent, CHAPS, Protoplasts 相似文献
18.
Seed germination and seedling growth as well as chlorophyll and carotenoid contents of mustard and gram seeds were inhibited or reduced significantly due to the treatment of different concentrations (100, 250, 500, 1000 and 2000 ng/ml) of aflatoxin B1. The range of inhibition in all the parameters was found to be directly influenced by the concentrations of toxin applied. Mustard and gram seedling germination inhibition assay can be used for aflatoxin B1. 相似文献
19.
Carlos O. Miller 《Planta》1979,146(4):503-511
Cells of a soybean tissue strain, suspended in an aerated liquid medium, caused disappearance of p-coumaric acid from the medium and oxidation of guaiacol, benzidine, pyrogallol, L-dihydroxyphenylalanine and L-epinephrine. Both the disappearance and the oxidations were inhibited by 6-benzylaminopurine (BAP) at a concentration of 0.5 mM. BAP at other concentrations either promoted or inhibited oxidation of epinephrine in precisely the pattern reported earlier for the disappearance of coumarate; therefore, the disappearance of coumarate probably involves its oxidation. The effectiveness of other cytokinins in inhibiting the oxidation was studied.At 0.5 mM, and perhaps even at 0.5 M, some of the several cytokinins tested inhibited oxygen consumption by the soybean cells. This inhibition, which did not require any of the above metabolizable compounds, was especially marked in the presence of cyanide, azide or Antimycin A, and was detectable in 10 min or less. Either Antimycin A or salicylhydroxamic acid alone promoted O2 consumption but together they were quite inhibitory. The soybean cells apparently have an alternate respiratory pathway and cytokinins may influence its operation.Several cytokinins at 0.5 mM, and perhaps at 0.5 M, also inhibited oxygen consumption by mitochondrial preparations from the soybean cells, the inhibition being evident in about 20 s. The consumption required a substrate such as malate, succinate or NADH. Cytokinins and related compounds varied in effectiveness as follows: BAP and 6-isopentenyla-minopurine 9-tetrahydropyranyl-BAP > kinetin, ribosyl-isopentenylaminopurine, 9-methyl-BAP and 9-methoxymethyl-BAP > 6,6-dimethylaminopurine and zeatin (slight activity) > 6-methylaminopurine, nicotinamide and adenine (ineffective). To a great extent this order parallels the order of effectiveness of the compounds in causing cell division. Mitochondria, therefore, may contain a site for an important cytokinin action.Abbreviations BAP
6-benzylaminopurine
- IPA
6-(2-isopentenyl)aminopurine 相似文献
20.
Szczerba MW Britto DT Ali SA Balkos KD Kronzucker HJ 《Journal of experimental botany》2008,59(12):3415-3423
The disruption of K(+) transport and accumulation is symptomatic of NH(4)(+) toxicity in plants. In this study, the influence of K(+) supply (0.02-40 mM) and nitrogen source (10 mM NH(4)(+) or NO(3)(-)) on root plasma membrane K(+) fluxes and cytosolic K(+) pools, plant growth, and whole-plant K(+) distribution in the NH(4)(+)-tolerant plant species rice (Oryza sativa L.) was examined. Using the radiotracer (42)K(+), tissue mineral analysis, and growth data, it is shown that rice is affected by NH(4)(+) toxicity under high-affinity K(+) transport conditions. Substantial recovery of growth was seen as [K(+)](ext) was increased from 0.02 mM to 0.1 mM, and, at 1.5 mM, growth was superior on NH(4)(+). Growth recovery at these concentrations was accompanied by greater influx of K(+) into root cells, translocation of K(+) to the shoot, and tissue K(+). Elevating the K(+) supply also resulted in a significant reduction of NH(4)(+) influx, as measured by (13)N radiotracing. In the low-affinity K(+) transport range, NH(4)(+) stimulated K(+) influx relative to NO(3)(-) controls. It is concluded that rice, despite its well-known tolerance to NH(4)(+), nevertheless displays considerable growth suppression and disruption of K(+) homeostasis under this N regime at low [K(+)](ext), but displays efficient recovery from NH(4)(+) inhibition, and indeed a stimulation of K(+) acquisition, when [K(+)](ext) is increased in the presence of NH(4)(+). 相似文献