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1.
Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO3 by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO3 at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d–1, or constant external concentrations ([NO3)of 3, 10, 20, and 100 mmol m–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d-1, although growth was notlimited by N supply at RAR =0.18 d-1. Growth rates showed littlechange with [NO3–] between 10–100 mmol m–3(RGR=0·15 –0·16 d-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO3, accumulation of NO3 in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO3 from 1 mol m–3 solutions were assessed relativeto the growth-related requirement for NO3, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d–1 , but decreased thereafter to a theoretical minimumvalue at RGR  相似文献   

2.
3.
REUVENI  J.; GALE  J.; ZERONI  M. 《Annals of botany》1997,79(2):191-196
Sodium chloride, at a concentration of 88 mol m-3in half strengthHoagland nutrient solution, increased dry weight per unit areaofXanthium strumarium L. leaves by 19%, and chlorophyll by 45%compared to plants grown without added NaCl at ambient (350µmol mol-1) CO2concentration. Photosynthesis, per unitleaf area, was almost unaffected. Even so, over a 4-week period,growth (dry weight increment) was reduced in the salt treatmentby 50%. This could be ascribed to a large reduction in leafarea (>60%) and to an approx. 20% increase in the rate ofdark respiration (Rd). Raising ambient [CO2] from zero to 2000 µmol mol-1decreasedRd in both control and salinized plants (by 20% at 1000, andby 50% at 2000 µmol mol-1CO2concentration) compared toRd in the absence of ambient CO2. High night-time [CO2] hadno significant effect on growth of non-salinized plants, irrespectiveof day-time ambient [CO2]. Growth reduction caused by salt wasreduced from 51% in plants grown in 350 µmol mol-1throughoutthe day, to 31% in those grown continuously in 900 µmolmol-1[CO2]. The effect of [CO2] at night on salinized plants depended onthe daytime CO2concentration. Under 350 µmol mol-1day-time[CO2], 900 µmol mol-1at night reduced growth over a 4-weekperiod by 9% (P <0.05) and 1700 µmol mol-1reduced itby 14% (P <0.01). However, under 900 µmol mol-1day-time[CO2], 900vs . 350 µmol mol-1[CO2] at night increasedgrowth by 17% (P <0.01). It is concluded that there is both a functional and an otiose(functionless) component to Rd, which is increased by salt.Under conditions of low photosynthesis (such as here, in thelow day-time [CO2] regime) the otiose component is small andhigh night-time [CO2] partly suppresses functional Rd, therebyreducing salt tolerance. In plants growing under conditionswhich stimulate photosynthesis (e.g. with increased daytime[CO2]), elevated [CO2] at night suppresses mainly the otiosecomponent of respiration, thus increasing growth. Consequently,in regions of adequate water and sunlight, the predicted furtherelevation of the world atmospheric [CO2] may increase plantsalinity tolerance. Xanthium strumarium ; respiration; photosynthesis; salt stress; sodium chloride; carbon dioxide; atmosphere  相似文献   

4.
Bunce  James A. 《Annals of botany》2001,87(4):463-468
Predicting responses of plant and global carbon balance to theincreasing concentration of carbon dioxide in the atmosphererequires an understanding of the response of plant respirationto carbon dioxide concentration ([CO2]). Direct effects of thecarbon dioxide concentration at which rates of respiration ofplant tissue are measured are quite variable and their effectsremain controversial. One possible source of variation in responsivenessis the energy status of the tissue, which could influence thecontrol coefficients of enzymes, such as cytochrome-c oxidase,whose activity is sensitive to [CO2]. In this study we comparedresponses of respiration rate to [CO2] over the range of 60to 1000 µmol mol-1in fully expanded leaves of four C3andfour C4herbaceous species. Responses were measured near themiddle of the normal 10 h dark period, and also after another24 h of darkness. On average, rates of respiration were reducedabout 70% by the prolonged dark period, and leaf dry mass perunit area decreased about 30%. In all species studied, the relativedecrease in respiration rate with increasing [CO2] was largerafter prolonged darkness. In the C3species, rates measured at1000 µmol mol-1CO2averaged 0.89 of those measured at 60µmol mol-1in the middle of the normal dark period, and0.70-times when measured after prolonged darkness. In the C4species,rates measured at 1000 µmol mol-1CO2averaged 0.79 of thoseat 60 µmol mol-1CO2in the middle of the normal dark period,and 0.51-times when measured after prolonged darkness. In threeof the C3species and one of the C4species, the decrease in theabsolute respiration rate between 60 and 1000 µmol mol-1CO2wasessentially the same in the middle of the normal night periodand after prolonged darkness. In the other species, the decreasein the absolute rate of respiration with increase in [CO2] wassubstantially less after prolonged darkness than in the middleof the normal night period. These results indicated that increasingthe [CO2] at the time of measurement decreased respiration inall species examined, and that this effect was relatively largerin tissues in which the respiration rate was substrate-limited.The larger relative effect of [CO2] on respiration in tissuesafter prolonged darkness is evidence against a controlling roleof cytochrome-c oxidase in the direct effects of [CO2] on respiration.Copyright 2001 Annals of Botany Company Carbon dioxide, respiration, Abutilon theophrasti(L.), Amaranthus retroflexus(L.),Amaranthus hypochondriacus (L.), Datura stramonium(L.), Helianthus annuus(L.), Solanum melongena(L.), Sorghum bicolor(L. Moench), Zea mays  相似文献   

5.
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   

6.
HESTNES  A. 《Annals of botany》1979,44(5):567-573
The distribution of exogenously-supplied radioactive labelledindol-3-yl-acetic acid (IAA) and gibberellin A1 (GA1) in geotropicallystimulated roots of Norway spruce (Picea abies (L.) Karst.)has been demonstrated. Seedlings were positioned with theirroot tips in 2.1 x 10–6 M [14C]IAA or 1.3 x 10–8m 3H-GA1 for 4 and 20 h, respectively. After geotropic stimulationfor 90 min in the horizontal position the root tips were cutlongitudinally in 50 µm thick sections, using a freeze-microtome.The radioactivity in the 14C-IAA treated roots occurred in higherconcentration in the lower than in the upper halves (ratio 1.25:1). A similar trend was observed in the [3H]GA1-treated rootswhere the ratio lower: upper halves was 2.04: 1. The ratio ofradioactivity in right and left halves of vertical roots wasapproximately the same in roots supplied with [14C]IAA and [3H]GA1(1.09: 1). The supplied radioactive compounds were analysed chromatographicallyafter extraction in methanol of 6 mm apical root segments. Onlya small fraction (7–8 per cent) of the supplied [14C]IAAwas revealed unchanged in the segments. The major part of thechromatographed, labelled compound has not been identified,but on basis of its RF value it is suggested that it may beindol-3-acetyl-aspartic acid (IAAasp). The chromatographic analysis of the [3H]GA,-treated segmentsshowed that only small fractions of this gibberellin has beenconverted to other compounds. These results have been discussed and correlated with knowledgeof plant growth regulators and their participation in root geotropism. Picea abies, spruce, geotropism, gibberellin A1, indol-3-yl-acetic acid, growth regulators, redistribution in roots  相似文献   

7.
The hypothesisof this investigation was that insulin and muscle contraction, byincreasing the rate of skeletal muscle glucose transport, would biascontrol so that glucose delivery to the sarcolemma (and t tubule) andphosphorylation of glucose intracellularly would exert more influenceover glucose uptake. Because of the substantial increases in blood flow(and hence glucose delivery) that accompany exercise, we predicted thatglucose phosphorylation would become more rate determining duringexercise. The transsarcolemmal glucose gradient (TSGG; the glucoseconcentration difference across the membrane) is inversely related tothe degree to which glucose transport determines the rate of glucoseuptake. The TSGG was determined by using isotopic methods in consciousrats during euglycemic hyperinsulinemia [Ins; 20 mU/(kg · min); n = 7], during treadmill exercise (Ex,n = 6), and in sedentary,saline-infused rats (Bas, n = 13).Rats received primed, constant intravenous infusions of trace3-O-[3H]methyl-D-glucoseand [U-14C]mannitol.Then2-deoxy-[3H]glucosewas infused for the calculation of a glucose metabolic index(Rg). At the end of experiments,rats were anesthetized, and soleus muscles were excised. Total soleusglucose concentration and the steady-state ratio of intracellular toextracellular3-O-[3H]methyl-D-glucose(which distributes on the basis of the TSGG) were used to calculateranges of possible glucose concentrations ([G]) at theinner and outer sarcolemmal surfaces([G]im and[G]om, respectively).Soleus Rg was increased in Ins andfurther increased in Ex. In Ins, total soleus glucose,[G]om, and the TSGGwere decreased compared with Bas, while[G]im remained near 0. In Ex, total soleus glucose and[G]im were increasedcompared with Bas, and there was not a decrease in[G]om as was observedin Ins. In addition, accumulation of intracellular free2-deoxy-[3H]glucoseoccurred in soleus in both Ex and Ins. Taken together, these dataindicate that, in Ex, glucose phosphorylation becomes an importantlimitation to soleus glucose uptake. In Ins, both glucose delivery andglucose phosphorylation influence the rate of soleus glucose uptakemore than under basal conditions.

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8.
We examined 1) whether the effects of lowered trans-sarcolemmal Na+ gradient on force differed between nonfatigued fast- and slow-twitch muscles of mice and 2) whether effects on action potentials could explain the decrease of force. The Na+ gradient was reduced by lowering the extracellular [Na+] ([Na+]o). The peak force-[Na+]o relationships for the twitch and tetanus were the same in nonfatigued extensor digitorum longus and soleus muscles: force was maintained over a large range of [Na+]o and then decreased abruptly over a much smaller range. However, fatigue was significantly exacerbated at a lowered [Na+]o that had little effect in nonfatigued soleus muscle. This finding suggests that substantial differences exist in the Na+ effect on force between nonfatigued and fatigued muscle. The reduced contractility in nonfatigued muscles at lowered [Na+]o was largely due to 1) an increased number of inexcitable fibers and threshold for action potentials, 2) a reduction of action potential amplitude, and 3) a reduced capacity to generate action potentials throughout trains. sodium gradient; muscle contraction; action potential train; extensor digitorum longus; soleus  相似文献   

9.
To study possible changes in the transport metabolites betweenchloroplasts and cytoplasm during CAM induction of Mesembryanthemumcrystallinum, we compared substrate specificity of P11 translocator(s)in isolated chloroplasts from the C3 and CAM-induced plants.The [14C]glu-cose 6-phosphate (G6P) transport activity was significantonly in the chloroplasts of CAM-mode plants and not detectablein those of C3-mode, while a similar high rate of [32P]Pi uptakewas observed with both types of chloroplasts. Kinetic analysisof G6P uptake in the CAM chloroplasts showed a high Vmax [10.6µmol (mg Chl)–1 h–1] and a comparatively lowKm value (0.41 mM); the latter was similar to Ki values of Pi,3-phosphoglycerate and phospho-enolpyruvate, 0.30, 0.34 and0.47 mM, respectively. On the other hand, [32P]Pi uptake inthe CAM chloroplasts was inhibited competitively by G6P witha Ki value (8.4 mM) 20-fold higher than the Km value for G6Puptake, while that in C3 chloroplasts was not inhibited at all.These results suggest that a new G6P/Pi, counterexchange mechanismis induced in the chloroplast envelope of CAM-induced M. crystallinumin addition to the ordinary type of P, translocator, that cannottransport G6P, already present in the C3-type chloroplasts. (Received March 17, 1997; Accepted May 10, 1997)  相似文献   

10.
The utilization of inorganic carbon and role of the coccolithswere investigated in intact cells and protoplasts of a marineunicellular calcareous alga, Emiliania huxleyi. Protoplastswith high photosynthetic activity were obtained by artificialdecalcification with 50 mM MES-NaOH (pH5.5). (1) The kineticsof the photosynthetic evolution of O2 at various concentrationsof externally added NaHCO3 were the same for intact cells andprotoplasts, indicating that the kinetic properties with respectto dissolved inorganic carbon (DIC) were not affected by thepresence or absence of the coccoliths on the cell surface. Double-reciprocalplots and plots of the concentration of substrate divided byvelocity (s/v) against the concentration of substrate (s) werebiphasic in the case of both intact cells and protoplasts. TheCO2-utilization reaction was, therefore, considered to involvetwo processes with different values of Km and Vmax. From thekinetic analyses, Km and Vmax [µmoles O2 (ml PCV)–1h–1] were deduced to be 92 µM and 76.3 for a "low-Km"reaction and 4.1 mM and 252 for a "high-Km" reaction, respectively.(2) In short-term (40-min) experiments, time courses of thetotal uptake of 14C-DIC and the incorporation of 14C into acid-stableproducts of photosynthesis and the internal pool of DIC, determinedas acid-labile compounds, under CO2-limiting conditions (80µM) were very similar for intact cells and protoplasts.However, incorporation of 14C into CaCO3 apparently occurredmore slowly in protoplasts than in intact cells. (3) In longterm (24-h) experiments, patterns of incorporation of 14C werealmost same for intact cells and protoplasts, with the exceptionthat the amount of 14C incorporated into CaCO3 was much smallerin the former than the latter. The production of Ca14CO3 increasedduring the course of 10 h after a 4-h lag. However, after 10h the level of Ca14CCO3 started to decrease. The decrease wasaccompanied by an increase in 14C in the products of photosynthesis,suggesting that CaCO3 was reutilized for the photosyntheticfixation of CO2 and, therefore, that the coccoliths functionas sites of storage of DIC. However, the internal level of DICremained at the same level even after the supply of externalDIC has been almost completely depleted. (Received July 25, 1995; Accepted December 11, 1995)  相似文献   

11.
To test thehypothesis that intracellular Ca2+activation of large-conductanceCa2+-activatedK+ (BK) channels involves thecytosolic form of phospholipase A2 (cPLA2), we first inhibited theexpression of cPLA2 by treating GH3 cells with antisenseoligonucleotides directed at the two possible translation start siteson cPLA2. Western blot analysis and a biochemical assay of cPLA2activity showed marked inhibition of the expression ofcPLA2 in antisense-treated cells.We then examined the effects of intracellularCa2+ concentration([Ca2+]i)on single BK channels from these cells. Open channel probability (Po) for thecells exposed to cPLA2 antisenseoligonucleotides in 0.1 µM intracellularCa2+ was significantly lower thanin untreated or sense oligonucleotide-treated cells, but the voltagesensitivity did not change (measured as the slope of thePo-voltagerelationship). In fact, a 1,000-fold increase in[Ca2+]ifrom 0.1 to 100 µM did not significantly increasePoin these cells, whereas BK channels from cells in the other treatmentgroups showed a normalPo-[Ca2+]iresponse. Finally, we examined the effect of exogenous arachidonic acidon thePoof BK channels from antisense-treated cells. Although arachidonic aciddid significantly increasePo,it did so without restoring the[Ca2+]isensitivity observed in untreated cells. We conclude that although [Ca2+]idoes impart some basal activity to BK channels inGH3 cells, the steepPo-[Ca2+]irelationship that is characteristic of these channels involves cPLA2.

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12.
The influence oflocal exposure to ozone (O3) onrespiratory epithelial permeability of sublobar lung segments wasstudied by using aerosolized99mTc-diethylenetriaminepentaacetic acid (DTPA; mol wt, 492). Two bronchoscopes were insertedthrough an endotracheal tube in anesthetized, mechanically ventilated,mixed breed dogs and were wedged into sublobar bronchi located in theright and left lower lobes, respectively. Segments were ventilated viathe bronchoscope with 5% CO2 inair delivered at 200 ml/min, and an aerosol of99mTc-DTPA was generated anddelivered through the scope and into the sublobar segment over a 30-speriod. Clearance of 99mTc-DTPAwas measured simultaneously from right and left lower lung segments atbaseline and 1, 7, and 14 days after a 6-h sublobar exposure tofiltered air or 400 parts per billionO3.O3 treatment significantlydecreased the clearance halftime(t50) of99mTc-DTPA by 50% from thebaseline mean of 32.3 to 16.0 min at 1 day postexposure. After 7 daysof recovery, t50was still reduced by 28.8%; however, by 14 days postexposure,clearance of 99mTc-DTPA hadrecovered, and thet50 had a meanvalue of 30.0 min. 99mTc-DTPAclearance was not altered by exposure to filtered air, andt50 values werecomparable to baseline at 1, 7, and 14 days postexposure. These resultsreveal that a single local exposure toO3 increases transepithelialclearance, but only for epithelia directly exposed toO3, and that 7-14 days ofrecovery are required before permeability to small-molecular-weightsolutes returns to normal.  相似文献   

13.
Carbonic anhydrase (CA, EC. 4.2.1.1 [EC] ) activity in air-grown Characorallina was detected mainly in the intracellular fraction,most of which composed of chloroplasts and cytoplasmic gel,and not on the cell surface. Only minor levels of CA activity,on the basis of equivalent volumes, were detected in the cellsap and the cytoplasmic sol. The maximum rate of photosynthetic O2 evolution by air-grownChara corallina at pH 6.0 was twice that at pH 7.6, while theapparent Km for external inorganic carbon (Ci) at pH 7.6 wasabout three times that at pH 6.0. However, the apparent Km(CO2)was about three times larger at pH 6.0 than at pH 7.6. The Km(Ci)-valueat pH 7.6 increased severalfold in the presence of acetazolamide(AZA), an inhibitor of CA, but no inhibition was observed atpH 6.0. The pH-dependence may be due to differences in the permeabilityof AZA at the given pH values. Fixation of 14CO2 at 20 µMand of H14CO3 at 200 µM over the course of 5 swas very similar at pH 7.4. Addition of CA significantly suppressedthe photosynthetic 14CO2-fixation but it stimulated the H14CO3-fixation.This result indicates that free CO2 is an active species ofCi that is incorporated into the cell during photosynthesis. These results together suggest the following: (1) Free CO2 isutilized for photosynthesis, (2) CA is mainly located insidethe cell and functions to increase the affinity for CO2 in photosynthesisby facilitating the supply of CO2 from the plasmalemma to thesite of CO2-fixation. 3Present address: Biological Laboratory, The University of theAir, Wakaba 2-11, Chiba, 260 Japan. (Received December 9, 1988; Accepted March 22, 1989)  相似文献   

14.
The effects ofMg2+ andBa2+ on single-channel propertiesof the inositol 1,4,5-trisphosphate receptor(IP3R) were studied by patch clampof isolated nuclei from Xenopusoocytes. In 140 mM K+ theIP3R channel kinetics and presenceof conductance substates were similar over a range (0-9.5 mM) offree Mg2+. In 0 mMMg2+ the channel current-voltage(I-V) relation was linear withconductance of ~320 pS. Conductance varied slowly and continuouslyover a wide range (SD  60 pS) and sometimes fluctuated during single openings. The presence of Mg2+ oneither or both sides of the channel reduced the current (blocking constant ~0.6 mM in symmetricalMg2+), as well as the range ofconductances observed, and made the I-V relation nonlinear (slopeconductance ~120 pS near 0 mV and ~360 pS at ±70 mV insymmetrical 2.5 mM Mg2+).Ba2+ exhibited similar effects onchannel conductance. Mg2+ andBa2+ permeated the channel with aratio of permeability of Ba2+ toMg2+ toK+ of 3.5:2.6:1. These resultsindicate that divalent cations induce nonlinearity in theI-V relation and reduce current by amechanism involving permeation block of theIP3R due to strong binding to site(s) in the conduction pathway. Furthermore, stabilization ofconductance by divalent cations reveals a novel interaction between thecations and the IP3R.

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15.
The loss of organic material from the roots of forage rape (Brassicanapus L.,) was studied by pulse-labelling 25-d-old non-sterilesand-grown plants with 14CO2. The distribution of 14C withinthe plant was measured at 0, 6 and 13 d after labelling whilst14 C accumulating in the root-zone was measured at more frequentintervals. The rates of 14C release into the rhizosphere, andloss of 14CO2 from the rhizosphere were also determined. Thesedata were used to estimate the accumulative loss of 14C fromroots and loss respiratory 14CO2 from both roots and associatedmicro-organisms. Approximately 17-19% of fixed 14CO2 was translocatedto the roots over 2 weeks, of which 30-34% was released intothe rhizosphere, and 23-24% was respired by the roots as 14CO2. Of the 14C released into the rhizosphere, between 35-51%was assimilated and respired by rhizosphere micro-organisms.Copyright1993, 1999 Academic Press Brassica napus L., carbon loss, carbon partitioning, microbial nutrition, microbial respiration, forage rape, pulse-labelling, rhizodeposition, root respiration, sand culture  相似文献   

16.
Cultures of water fern Azolla pinnata R. Br. exposed for 1 weekto either 30, 50 or 80 nl l-1 O3 showed significant reductionsin rates of growth and N2 fixation, and had fewer heterocysts.Although the levels of glutamine synthetase (GS) and glutamatedehydrogenase (GDH) activity were decreased by low concentrationsof O3 exposures (30 or 50 nl l-1), significant increases inlevels of the same enzymes were caused by higher concentrationsof O3 (80 nl l-1). Increased levels of total protein, polyamines(putrescine and spermidine), and the xanthophyll-cycle precursorof abscisic acid (ABA), violaxanthin, were also found with higherlevels of O3 (80 nl l-1). Levels of ABA itself were significantlyincreased by low level O3 fumigation (30 nl l-1) but significantlydecreased by exposure to 80 nl l-1 O3. This may indicate thathigher levels of atmospheric O3 inhibit the final stages ofABA biosynthesis from violaxanthin.Copyright 1994, 1999 AcademicPress Abscisic acid, nitrogen assimilation, nitrogen fixation, ozone pollution, polyamines, violaxanthin  相似文献   

17.
Earlier work has established that the saturable component ofuptake of RS-[214C]ABA by bean (Phaseolus coccineus L. cv. Prizewinner)root segments can be attributed to the action of a carrier.We now show that the carrier-mediated uptake is unaffected byRS-2-trans-ABA and lunularic acid and the unnatural R-ABA alsoappears to be ineffective. The specificity for S-ABA requiresthe halving of the Km value for ABA determined previously (2.6mmol m-3 for RS-; 1.3 mmol m-3 for S-ABA). The RS-1', 4'-cis-dioland RS-1'-deoxy ABA reduce the uptake of RS-[2-14C]ABA aboutas strongly as does unlabelled ABA, the K1 for 1'-deoxy ABAwas similar to the Km for ABA. The K1 for RS-1', 4'-trans-diolwas 15.7 mmol m-3. Consideration of the stereochemistry of thesecompounds suggests that the face of the ring of ABA away fromthe 1'-hydroxyl group interacts with the carrier site. Labelled material diffused out of undamaged root surfaces whichhad absorbed RS-[3H]ABA through an apical cut, suggesting thatABA is present in the apoplast. A simplified hypothesis is presented that can account for polartransport of ABA based on a gradient of a carrier in a tissuebut where the carrier is distributed uniformly on the apicaland basal ends of each cell. Key words: Uptake carrier, Abscisic acid, 1', 4'-Diol, Lunularic acid, Phaseolus coccineus, Polar-transport, Deoxyabscisic acid  相似文献   

18.
In 14C fixation experiments, 3-phosphoglyceric acid was thefirst product of carbon assimilation in the light in Potamogetonpectinatus. The pattern of early 14C-labelled compounds wasthe same over a range of pH values of the medium from 3.5 to8.1. Rates of 14C incorporation declined with increasing pHof the medium indicating that free CO2 is the major exogenoussource of carbon for photosynthesis in Potamogeton pectinatus.  相似文献   

19.
The role of nitric oxide (NO) in the occurrence of intracellular Ca2+ concentration ([Ca2+]i) oscillations in pituitary GH3 cells was evaluated by studying the effect of increasing or decreasing endogenous NO synthesis with L-arginine and nitro-L-arginine methyl ester (L-NAME), respectively. When NO synthesis was blocked with L-NAME (1 mM) [Ca2+]i, oscillations disappeared in 68% of spontaneously active cells, whereas 41% of the quiescent cells showed [Ca2+]i oscillations in response to the NO synthase (NOS) substrate L-arginine (10 mM). This effect was reproduced by the NO donors NOC-18 and S-nitroso-N-acetylpenicillamine (SNAP). NOC-18 was ineffective in the presence of the L-type voltage-dependent Ca2+ channels (VDCC) blocker nimodipine (1 µM) or in Ca2+-free medium. Conversely, its effect was preserved when Ca2+ release from intracellular Ca2+ stores was inhibited either with the ryanodine-receptor blocker ryanodine (500 µM) or with the inositol 1,4,5-trisphosphate receptor blocker xestospongin C (3 µM). These results suggest that NO induces the appearance of [Ca2+]i oscillations by determining Ca2+ influx. Patch-clamp experiments excluded that NO acted directly on VDCC but suggested that NO determined membrane depolarization because of the inhibition of voltage-gated K+ channels. NOC-18 and SNAP caused a decrease in the amplitude of slow-inactivating (IDR) and ether-à-go-go-related gene (ERG) hyperpolarization-evoked, deactivating K+ currents. Similar results were obtained when GH3 cells were treated with L-arginine. The present study suggests that in GH3 cells, endogenous NO plays a permissive role for the occurrence of spontaneous [Ca2+]i oscillations through an inhibitory effect on IDR and on IERG. voltage-gated potassium channels; ether-à-go-go-related gene potassium channels; slow-inactivating outward currents; fast-inactivating outward currents  相似文献   

20.
The use of chlorate as an analogue for NO3 during nitrateuptake into Chara corallina cells has been investigated. NO3inhibits 36C1O3 influx into Chara over the concentrationrange 0–1000 mmol m–3. Lineweaver-Burke plots ofthe data are characteristic of competitive inhibition by NO–3in the low concentration range (0–300 mmol m–3 ClO3)and apparent KINO3 is 140 mmol m–3 which is of a similarorder of magnitude as apparent KmCIO3- 180 mmol m–3. Athigher substrate concentrations the inhibition by NO3was not characteristic of competitive or uncompetitive inhibition. 36C1O3/NO3 influx was dependent on K+ and Ca2+in the external medium and inhibited by FCCP. NO3 pretreatmentor N starvation increased subsequent 36C1O3/NO3influx into Chara. A comparison between rates of net NO3uptake and 36C1O3/NO3 influx supported the previoushypothesis that NO3 efflux is an important componentin the determination of overall uptake rates. Key words: Nitrate, Chara, 36CIO3  相似文献   

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