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1.
Root growth of 7-d-old wheat (Triticum aestivum cv. Gamenya)seedlings was impaired at dissolved O2 concentrations of 0.01and 0.055 mol m3 O2, while growth at 0.115 mol m3O2 was the same as that in continuously aerated controls (0.26mol m3 O2). Oxygen uptake by apical (02 mm), expanding (24mm) and expanded (1012 mm) tissues of the roots decreasedbelow 0.16, 0.09 and 0.05 mol m3 O2, respectively. Thishierarchy is consistent with the metabolic rates of these tissues.There was a small (c. 9%) inhibition of O2 uptake and some netsynthesis of ethanol and alanine in root apices at 0.115 molm3 O2. Significant amounts of anaerobic end-productsaccumulated at 0.055 mol m3 O2 and even more so at 0.01mol m3 O2, indicating that oxidative phosphorylationwas strongly inhibited. Net alanine synthesis increased in fully expanded (1016mm) tissues exposed to <0.0030.01 mol m3 O2,and this increase was accompanied either by a proportionallysmaller increase in the concentration of other free amino acidsor by a net decrease in free amino acid levels excluding alanine.This suggests that alanine was synthesized as an end-productof anaerobic catabolism and did not accumulate simply becauseof decreased net protein synthesis. Comparing the carbon flow to CO2, ethanol, lactate and alaninein roots at 0.01 mol m3 O2 with carbon loss as CO2 inaerated roots suggests that carbon flow to products of metabolismwas not greatly enhanced due to O2 deficiency. This infers,but does not prove that, in wheat, generation of energy duringperiods of O2 deficiency is not enhanced due to a Pasteur effect. Key words: Anaerobic, fermentation, oxygen, wheat 相似文献
2.
The Combined Effects of Salinity and Root Anoxia on Growth and Net Na+ and K+-accumulation in Zea mays Grown in Solution Culture 总被引:2,自引:0,他引:2
The effects of excess salinity and oxygen deficiency on growthand solute relations in Zea mays L. cv. Pioneer 3906 were examinedin greenhouse experiments. The roots of plants 14 d old growingin nutrient solution containing additions of NaCl in the range1.0200 mol m3 were either exposed to a severedeficiency of O2 by bubbling with nitrogen gas (N2 treatment),or maintained with a supply of air (controls), for a periodof 17 d. The threshold NaCl concentration resulting inappreciable inhibition of leaf extension, and shoot f. wt gainin controls was between 10 and 25 mol m3. At 25 mol m3NaCl the ratio of Na+/K+ transported to shoots was about 20times greater than in plants in 1.0 mol m3 NaCl. Theeffect of addition of NaCl to the nutrient solution was to enhanceNa+ movement but simultaneously depress the rate of K+ transportto shoots (per g f. wt roots). Interactions between NaCl levels and aeration treatment wereshown by analyses of variance to be statistically significantfor leaf extension, shoot and root f. wt gains, Na+ and K+ concentrationsin shoots and roots. When roots were N2-treated, shoot and rootgrowth were depressed, the effect of aeration treatment beinggreatest at NaCl concentrations of 50 mol m3 or less.Additionally, N2-treatment greatly accelerated Na- transportto shoots while depressing K+ transport still further, so thatat 10 mol m3 NaCl the ratio Na+/K+ acquired by the shootswas 230 times greater than in controls. Over the concentrationrange 1.0 to 50 mol m3 NaCl, the ratio Na+/K+ transportedto shoots by anoxic roots increased by a factor of 860. Mechanisms controlling changes in solute flux to the shoot,and the significance in relation to plant tolerance of excesssalts or oxygen deficiency are discussed. Anaerobic, corn, flooding, maize, oxygen-deficiency, salinity 相似文献
3.
Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown as simulated swards for 71 d in flowing nutrientsolutions with roots at 11 C and shoots at 20/15 C, day/night,under natural illumination. Root temperatures were then changedto 3, 5, 7, 11, 13, 17 or 25 C and the total N2, fixation over21 d was measured in the absence of a supply mineral N. Alltreatments were subsequently supplied with 10 mmol m2NO2 in the flowing solutions for 14 d, and the relativeuptake of N by N2, fixation and NO3 uptake was compared.Net uptake of K+ was measured on a daily basis. Root temperature had little effect on root d. wt over the 35-dexperimental period, but shoot d. wt increased by a factor of3.5 between 3 and 25 C, with the sharpest increase occurringat 711 C. Shoot: root d. wt ratios increased from 25to 68 with increasing temperature at 725 C. N2-fixationper plant (in the absence of NO2 ) increased with roottemperature at 313C, but showed little change above13 C. The ratios of N2 fixation: NO2 uptake over 14d (mol N: mol N) were 0.470.77 at 37 C, 092154at 1117 C, and 046 at 25 C, reflecting the dominanceof NO3 uptake over N2 fixation at extremes of high andlow root temperature. The total uptake of N varied only slightlyat 1125 C (095110 mmol N plant1),the decline in N2 fixation as root temperature increased above11 C was compensated for by the increase in NO 3 uptake.The % N in shoot dry matter declined with decreasing root temperature,from 32% at 13 C to 15% at 3 C. In contrast, concentrationsof N expressed on a shoot water content basis showed a modestdecrease with increasing temperature, from 345 mol m3at 3 C to 290 mol m3 at 25 C. Trifolium repens L, white clover, root temperature, N2 fixation, potassium uptake, nitrate uptake, flowing solution culture 相似文献
4.
Radial Turgor Pressure Profiles in Growing and Mature Zones of Wheat Roots--A Modification of the Pressure Probe 总被引:4,自引:1,他引:3
PRITCHARD J.; WILLIAMS G.; JONES R G. WYN; TOMOS A. D. 《Journal of experimental botany》1989,40(5):567-571
A modification of the pressure probe is described which allowsaccurate routine recording of the turgor pressure of singlecells at measured depth within a tissue. Measurements of radial profiles of turgor pressure in wheatroots grown in some simple salt solutions (0.5 mol m3CaCl2, 0.5 mol m3 CaCI2 plus 10 mol m3 NaCl, and0.5 mol m3 CaCl2 plus 10 mol m3 KCI), are described.Turgor pressure was constant (approximately, 0.65 MPa) alonga radius within the elongation zone irrespective of the natureof the bathing solution. In mature root tissue turgor pressurein the cortex was lower than that of the growing zone in alltreatments and the pressure of the stele was on average 0.22MPa higher than that of the cortex. Potassium in the mediumbathing the root increased the turgor pressure in mature root(both cortex and stele) relative to low salt and sodium treatments. The results are discussed in relation to both root growth andion accumulation. Key words: Pressure probe, wheat roots, salt solution 相似文献
5.
Ricinus communis L. (castor bean) plants were grown in the absence(control) and in the presence of 100molm3NaCl with areciprocal split-root system, in which K+ was supplied to oneand NO3 to the other part of the root system. In theseplants shoot and, to a lesser extent, total root growth wereinhibited compared to plants with non-split roots. Without andwith NaCl, growth of roots receiving NO3 but noK+ (minusK/plus N-roots) was substantially more vigorous thanunder the reverse conditions (plus K/minus N-roots1).100mol m3 NaCl inhibited growth of minus K/plus N-roots1to the same extent as that of non-split roots, indicating thatexternally supplied K+ was not required for root growth undersaline conditions. In growth media without added K+ the rootdepleted the external low K + levels resulting from chemicalsdown to a minimum value Cmln (1.0 to 1.4 mmol m3); inthe presence of 100 mol m3 NaCl, Cmin, was higher (1018mmol m3) and resulted from an initial net loss of K +.Cmin, was pH-dependent The distribution of K+, Na+ and Mg2+along the root was measured. In meristematic root tissues, K+ concentrations were scarcely affected by external K+ or byNaCl, where Na + concentrations were low, but somewhat elevatedat low external K+ and/or high NaCl. In differentiated, vacuolatedtissues K + concentrations were low and Na+ concentrations high,if K + was not supplied externally and/or NaCl was present.The longitudinal distribution of ions within the root was usedto estimate cytoplasmic and vacuolar ion concentrations. Thesedata showed a narrow homoeostasis of cytoplasmic K+ concentrations(100140 mol m3) independent of external K + supplyeven in the presence of 100 mol m 3 NaCl. CytoplasmicNa + concentrations were maintained at remarkably low levels.Hence, external K+ concentrations above Cmin, were not requiredfor maintaining K/Na selectivity, i.e. for controlling Na+ entry.The results are discussed with regard to mechanisms of K/Naselectivity and to the importance of phloem import of K+ forsalt tolerance of roots and for cytoplasmic K+ homoeostasis. Key words: Ricinus communis, nitrate, potassium, root (split-root), salt tolerance, phloem transport 相似文献
6.
Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m3 CaCl2 r, P, Y and were20.7±4.6 µm min1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min1MPa1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m3 KC1 these parametersbecame 12.3±3.5 µm min1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min1MPa1. After 24 h osmotic adjustment in 150 mol m3mannitol/0.5 mol m3 CaCl2 r= 19.6±4.2 µmmin1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min1 MPa01, respectively.After 24 h growth in 350 mol m3 mannitol/0.5 mol m3CaCl2 r= 13.3±4.1 µm min1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min1MPa1. During osmotic adjustment in 200 mol m3mannitol/0.5 mol m3 CaCl2, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min1MPa1. Therefore, Y and are influenced by 10 mol m3 K+ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur 相似文献
7.
Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina (Forsk.) Vierh.) 总被引:2,自引:0,他引:2
The roots of young plants of Avicennia marina (Forsk.) Vierh.grown under simulated tidal conditions were harvested so asto obtain the entire root system. The roots were subdividedand weighed and subsamples taken for manometric determinationof respiration rates at different temperatures. The supply capacityof the above-ground portion of the root system was determinedand the results compared in terms of supply and demand. Theoxygen consumption rate of the roots at 15°C was found tobe 1·69±0·07 µmol kg1 s1for cable roots and 3·27±0·12 µmolkg1 s1 for fine roots. The Q10 for respirationwas 2·55 for oxygen consumption in both fine and cableroots, and for carbon dioxide production was 2·66 forfine roots and 3·04 for cable roots. The respiratoryquotient varied with temperature but was less than unity. Concentrationdifferences of between 1·8 mol m3 and 3·4mol m3 between the inside of root and the air were sufficientto permit aeration of the root system by diffusion alone, andthe aerenchyma contained sufficient oxygen to maintain aerobicconditions while the roots were covered with water. The effectof tide and seasonal temperature change on gas exchange, togetherwith the possibility of some form of carbon dioxide fixationwithin the root, are examined and the implications of theseeffects on growth and development are discussed. Key words: Mangrove, root aeration, respiration, aerenchyma 相似文献
8.
Spatial and Temporal Aspects of Growth in the Primary Root of Cotton Seedlings: Effects of NaCl and CaCl2 总被引:1,自引:0,他引:1
Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) weregrown in modified Hoagland nutrient solution with various combinationsof NaCl and CaCl2. Marking experiments and numerical analysiswere conducted to characterize the spatial and temporal patternsof cotton root growth at varied Na/Ca ratios. At 1 mol m3Ca, 150 mol m3 NaCl reduced overall root elongation rateto 60% of the control, while increasing Ca to 10 mol m3at the same NaCl concentration restored the elongation rateto 80% of the control. Analysis of the spatial distributionof elongation revealed that the presence of 150 mol m3NaCl in the medium shortened the growth zone by about 2 mm fromthe approximate 10 mm in the control and also reduced the relativeelemental elongation rate (i.e. the longitudinal strain rate,defined as the derivatives of displacement velocity of a cellularparticle with respect to position on root axis). Supply of 10mol m3 Ca at the high salt condition restored partiallythe relative elemental elongation rate, but not the length ofthe growth zone. Compared to the control, the growth trajectoriesshowed that at 1 mol m3 CaCl2 it took more time for acellular particle to move through the growth zone at 150 molm3 NaCl, while at 10 mol m3 CaCl it took lesstime and there was no difference between the NaCl treatments Key words: Gossypium hirsutum, salinity stress, root growth kinematics 相似文献
9.
This paper reports the effects of low O2 concentration (001,0055, and 0.115mol m3) in nutrient solutions onK+/Na+ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O2 uptake,K+ uptake and K+/Na+ selectivity were all more pronounced and/oroccurred at higher external O2 concentrations in the apex (02mm) than in the expanding tissues (24 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (412 mm). Selectivity for K+ over Na+ in roots and shoots was particularlysensitive to O2 deficiency. For example, in apical tissues (02mm) K + /Na+ selectivity was already reduced at 0.115 mol m3O2, yet at this O2 concentration there was no effect on eithergrowth or (K+/Na+) uptake. Upon transfer from 0.01 to 0.26 mol m3 O2, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K+ + Na+) concentrations and K+/Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K+ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K+/Na+ selectivity, expanded and expanding tissues 相似文献
10.
Hypoxia Induces Membrane Depolarization and Potassium Loss from Wheat Roots but does not Increase their Permeability to Sorbitol 总被引:8,自引:2,他引:6
BUWALDA F.; THOMSON C. J.; STEIGNER W.; BARRETT-LENNARD E. G.; GIBBS J.; GREENWAY H. 《Journal of experimental botany》1988,39(9):1169-1183
This paper deals with the responses of roots of wheat {Triticumaestivum L.) to hypoxia with special emphasis on the effectsof severe O2 deficiency on membrane integrity, loss of K+ fromthe root and root membrane potentials. Seminal and crown roots of 26-d-old plants exposed to severehypoxia (0.003 mol O2 m3) for 3 h or 10 d prior to excisionand subsequently exposed to hypoxic solutions, had slightlylower rates of sorbitol influx and a slightly smaller apparentfree space than roots in aerated solutions. These results indicatethat neither a few hours nor a 10-d exposure to hypoxia hadadverse effects on the membrane integrity of the bulk of thecells in the roots. However, both 6-d-old seedlings and 26-d-oldplants lost K+ from the roots following their transfer fromaerated to hypoxic nutrient solutions. In the 26-d-old plants,which were of high nutritional status, there was a net K+ effluxfrom the roots to the external solution. In contrast, with the6-d-old seedlings, which were of low nutritional status, thedecrease in the K+ content of the roots was smaller than thenet K+ uptake to the shoots. Exposure of excised roots to 0.008 mol O2 m3caused arapid and reversible membrane depolarization from 120to 80 mV. These data and the magnitude of thenet effluxes strongly suggest that K+ losses during the earlystages of hypoxia are due to membrane depolarization ratherthan to increases in the permeability of membranes to K +. Key words: Hypoxia, membrane integrity, membrane potentials, seminal and crown roots 相似文献
11.
Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.) 总被引:2,自引:0,他引:2
Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m1 (34.2 mol m3 NaCl)and nodulation was completely inhibited at 7 dS m1 (61.6mol m3 NaCl); the plants died at 8 dS m1 (71.8mol m3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 14 dS m1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N2 fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N2 fixation, Rhizobium, salinity 相似文献
12.
The relationships between CO2 concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO2 supply around the roots. Free CO2 in sediment-interstitial-waterranged from 101 mol m3 (Esthwaite), 0.79 mol m3(peat), 0.32 mol m3 (silt) and 017 mol m3(sand), with plants maintained under PAR of 40 µmol m2s1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO2 had larger leaf fresh weight (069 g) andtotal surface area (223 cm2 g1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm2g1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO2 concentration[CO2], was highest in the sand-grown plants (269 molm3, corresponding to 6.5% CO2 in air) and lowest inthe Esthwaite plants (108 mol m3). Expressionof CAM in transplants was also greatest in the low CO2 regime,with H+ (measured as dawn-dusk titratable acidity) of 50µmolg fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO2]1 and would makea major contribution to daytime CO2 fixation in vivo. A range of leaf sections (02, 10, 50 and170 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO2 evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO2 and 10mol m3 exogenous CO2 was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O2 g1 fr. wt. h1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO2 g1 fr. wt. h1) with a K0.5 of 80 mmol m3.In terms of light response, saturation of photosynthesis intissue slices occurred at 8501000 µmol m2s1 although light compensation points (611 µmolm2s1) and chlorophyll a: b ratios (1.3) were low.While CO2 and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO2 supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO2 concentrating mechanisms interact inintact plants to maintain saturating CO2 levels within leaflacunae, although the responses of the various components ofCO2 supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO2 concentration, crassulacean acid metabolism, root inorganic carbon supply, CO2 concentrating mechanism 相似文献
13.
Nitrate Inhibition of Chloride Influx in Barley: Implications for a Proposed Chloride Homeostat 总被引:6,自引:0,他引:6
Net accumulation of Cl by intact barley plants was virtuallyeliminated in roots and reduced by 40% in shoots when externalmedia (0.5 mol m3 CaSO4 plus 05 mol m3KCI) were supplemented with 0.25 mol m Ca(NO3)2. Plasmalemma36Cl influx (oc) was shown to be insensitive to externalNO3- in plants which had previously been grown in solutionslacking 3, but oc became sensitive to NO3-after a lagperiod of 36 h. Kinetic analyses revealed that the inhibitionof 36C1 influx by external NO3- was complex. At 0.25mol m3 NO3- the Vmax for Cl influx was reducedby greater than 50%, with insignificant effects upon Km. At0.5 mol m3 NO3- there was no further effect upon Vmaxbut Km for influx increased from 38±5 mmol m3to 116±26 mmol m3. By contrast, Cl effluxwas found to be insensitive to external NO3-. A model for theregulation of Cl influx is proposed which involves bothnegative feedback effects from vacuolar NO3- +Cl) concentrationand (external) NO3- inhibition of Cl influx at the plasmalemma.These combined effects serve to discriminate against Claccumulation, favouring NO3- accumulation, when the latter ionis available. Such observations are inconsistent with recentproposals for the existence of bona fide homeostats for chlorideaccumulation in higher plants. Key words: Nitrate inhibition, Chloride influx, Barley 相似文献
14.
Munns, R. 1985. Na+, K+ and Cl in xylem sap flowing toshoots of NaCl-treated barley.J. exp. Bot. 36: 10321042. Na+, Cl and K+ concentrations were measured in xylemsap obtained by applying pressure to the roots of decapitatedbarley plants grown at external [NaCl] of 0, 25, 50, 100, 150and 200 mol m3. For any given NaCl treatment, ion concentrationsin the xylem sap were hyperbolically related to the flux ofwater. Ion concentrations in sap collected at very low volumefluxes (without applied pressure) were 510 times higherthan in sap collected at moderate fluxes (under pressure). Fora given moderate volume flux, Na+ concentration in the xylemsap, [Na+]x, was only 4.0 mol m3 at external [NaCl] of25150 mol m3, and increased to 7.0 mol m3at 200 mol m3. [Cl-]x showed a similar pattern. Thisshows there would be little difference in the rate of uptaketo the shoot of plants at 25150 mol m3 externalNaCl and indicates little change even at 200 mol m-3 NaCl becausetranspiration rates would be much lower. Thus the reduced growthof the shoot of plants at high NaCl concentrations is not dueto higher uptake rates of Na+ or Cl. The fluxes of Na+, Cl and K increased non-linearlywith increasing volume flux indicating little movement of saltin the apoplast. The flux of K+ increased even when [K+]x wasgreater than external [K+], indicating that membrane transportprocesses modify the K+ concentration in the transpiration streamas it flows through the root system. Key words: -Xylem sap, Na+, K+, Cl fluxes, salinity, barley 相似文献
15.
Salt Stress Causes Acceleration of Purine Catabolism and Inhibition of Pyrimidine Salvage in Zea mays Root Tips 总被引:1,自引:0,他引:1
PETERSON TODD A.; LOVATT CAROL J.; NIEMAN RICHARD H. 《Journal of experimental botany》1988,39(10):1389-1395
Nucleotide metabolism was studied in apical 5.0 mm root tipsof corn plants (Zea mays L., cv. Pioneer 3906) hydroponicallycultured for 7 d and then salinized for 19 d at a rate calculatedto reduce the osmotic potential (o) of the solutions by O.1MPad1 to a final o = -0.4 MPa. Saline treatments withtwo different molar ratios of Ca2+/Na+ were employed, viz.,003 (2.5 mol m3 CaCl2 + 86.5 mol m3 NaCl)for the NaCl treatment and 0.73 (31.5 mol m3 CaCl2 +43.1 mol m3 NaCl) for the NaCl + CaCl2 treatment. Bothsalt treatments reduced root growth by more than 30%. The capacityof roots to provide purine nucleotides either by de novo synthesisor by re-utilization of existing bases, e.g. salvage of hypoxanthineto adenine nucleotides, was not affected by either salt treatment.However, catabolism of hypoxanthine was accelerated more than3.5-fold by both salt treatments, demonstrating an increasedcapacity for purine catabolism which would shift the normal1: 1 ratio of synthesis: degradation of purine nucleotides observedfor the roots of healthy control plants to less than 0.2 duringsalt stress. The ratio of pyrimidine nucleotide synthesis: degradationwas also reduced. In this case, the unfavourable shift towardnucleotide degradation resulted because both salt treatmentsreduced salvage capacity by more than 25%, but had no compensatingeffect on de novo synthesis or catabolism of pyrimidines. Key words: Salinity, osmotic potential, nucleotide metabolism 相似文献
16.
Regulation of Sulphate Transport in a Tropical Legume, Macroptilium atropurpureum, cv. Siratro 总被引:2,自引:0,他引:2
CLARKSON DAVID T.; SMITH FRANK W.; BERG PETER J. VANDEN 《Journal of experimental botany》1983,34(11):1463-1483
When young plants of Macroptilium atropurpureum, cv. Siratrowere deprived of external sulphate (-S plants) growth of shootsand roots continued at rates comparable to those in plants wellsupplied with sulphate (control) for 3 d and 5 d respectively.Dilution of internal sulphur therefore took place and redistributionof sulphur occurred between inorganic and organic forms andbetween roots and younger leaves. Even when S-deficiency limitedgrowth, plants contained 16% of their total sulphur as sulphate,but most of this was retained in old leaves and redistributedslowly to growing zones. The capacity for sulphate uptake increased in roots of Splants very soon after they were deprived of external sulphate;within 24 h the absorption from 0.25 mol m3 SO42was more than five times that of control roots. Maximum increasedcapacity was reached after 23 d stress when the Vmaxof system 1 was 1948 nmol h1g1root fr. wt. inS plants and 337 nmol h1g1root fr. wt.in controls. The Kmfor system 1 did not change significantlywith S-stress being between 58 µM in both setsof plants. Absorption of L-cysteine was not stimulated by S-stress. There was a close, positive relationship between plant growthrate and the rate at which sulphate uptake capacity was enhancedby withholding sulphate from culture solutions. When S plants were replaced in sulphate-containing solutiontheir capacity for SO42 declined to the control levelwithin 24 h. Very marked repression of capacity was also foundwhen S plants were treated with L-cysteine, but therewas no immediate effect with methionine. Roots of this species appear to have a very active system fordegrading L-cysteine to sulphate, 30% of the label in 35S-cysteineabsorbed by roots was recovered in 35SO42 after 20 minor 2 h incubation. By contrast, roots had a very weak abilityto reduce sulphate. When part of the root system was in solution lacking sulphatethere was enhanced uptake of sulphate by other parts which themselveswere amply supplied with sulphate. This is seen as an exampleof compensatory absorption. The response to S-stress is specific and there were no positiveinteractions between S-stress and the absorption of phosphate,or P-stress and the uptake of sulphate. The results are discussed in relation to the close control ofsulphate uptake by internal sulphate concentration, redistributionof forms of sulphur during stress and mobility of sulphate inthe phloem. Key words: Kinetics, Amino-S, Sulpholipid, Repression;, Deficiency 相似文献
17.
Influence of nitrate on uptake of ammonium by nitrogen-depleted soybean: is the effect located in roots or shoots? 总被引:4,自引:1,他引:3
Saravitz Carole H.; Chaillou Sylvain; Musset Joanne; Raper C. David Jr.; Morot-Gaudry Jean-Francis 《Journal of experimental botany》1994,45(11):1575-1584
In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom]plants that were subjected to 15 d of nitrogen deprivation inflowing hydroponic culture, concentrations of nitrogen declinedto 1.0 and 1.4mmol Ng1 dry weight in shoots and roots,respectively, and the concentration of soluble amino acids (determinedas primary amines) declined to 40µmol g1 dry weightin both shoots and roots. In one experiment, nitrogen was resuppliedfor 10 d to one set of nitrogen-depleted plants as 1.0 mol m3NH4+ to the whole root system, to a second set as 0.5 mol m3NH4+ plus 0.5 mol m3 NO3 to the whole root system,and to a third set as 1.0 mol m3 NH4+ to one-half ofa split-root system and 1.0 mol m3 NO3 to theother half. In a second experiment, 1.0 mol m3 of nitrogenwas resupplied for 4 d to whole root systems in NH4+ : NO3ratios of 1:0, 9:1, and 1:1. Nutrient solutions were maintainedat pH 6.0. When NH4+ was resupplied in combination with NO3 to thewhole root system in Experiment I, cumulative uptake of NH4+for the 10 d of resupply was about twice as great as when NH4+was resupplied alone. Also, about twice as much NH4+ as NO3was taken up when both ions were resupplied to the whole rootsystem. When NH4+ and NO3 were resupplied to separatehalves of a split-root system, however, cumulative uptake ofNH4+ was about half that of NO3. The uptake of NH4+,which is inhibited in nitrogen-depleted plants, thus is facilitatedby the presence of exogenous NO3, and the stimulatingeffect of NO3 on uptake of NH4+ appears to be confinedto processes within root tissues. In Experiment II, resupplyof nitrogen as both NH4+ and NO3 in a ratio of either1:1 or 9:1 enhanced the uptake of NH4+. The enhancement of NH4+uptake was 1.8-fold greater when the NH4+: NO3-resupplyratio was 1:1 than when it was 9:1; however, only 1.3 timesas much NO3 was taken up by plants resupplied with the1 :1 exogenous ratio. The effect of NO3 on enhancementof uptake of NH4+ apparently involves more than net uptake ofNO3 itself and perhaps entails an effect of NO3uptake on maintenance of K+ availability within the plant. Theconcentration of K+ in plants declined slightly during nitrogendeprivation and continued to decline following resupply of nitrogen.The greatest decline in K+ concentration occurred when nitrogenwas resupplied as NH4+ alone. It is proposed that decreasedavailability of K+ within the NH4+-resup-plied plants inhibitedNH4+ uptake through restricted transfer of amino acids fromthe root symplasm into the xylem. Key words: Ammonium, Glycine max, nitrate, nitrogen-nutrition, nitrogen stress, split-root cultures 相似文献
18.
Influx and Efflux of Nitrate and Ammonium in Italian Ryegrass and White Clover Roots: Comparisons Between Effects of Darkness and Defoliation 总被引:9,自引:2,他引:7
Seedlings of Italian ryegrass (Lolium multiflorum Lam. cv. RVP)and clonal stolon cuttings of white clover (Trifolium repensL. cv. Blanca) were grown for 19 d in flowing solution culture,with N supplied as either 250 mmol m3 NO3 or NH3+.Rates of net uptake, influx and translocation of NO3and NH4+ were then determined using 15N and 13N labelling techniques:between 35 h into the photoperiod following 8 h darknessfor white clover (CL), and for ryegrass plants that were eitherentire (IL) or with shoots excised 90 min prior to 13N influx(IC); and 75 min into the photoperiod following 3739h darkness for ryegrass (ID). Rates of net uptake, influx andefflux of NH4+ exceeded those of NO3 in IL and IC ryegrassplants: the opposite occurred in white clover (CL). The decreasein net uptake following defoliation of ryegrass was greaterfor NH4+ (62%) than NO3 (40%). For NH4+ this was associatedwith a large decrease in influx from 110 to 6.0µmol h1g1 root fr. wt; but for NO3, influx only decreasedfrom 42 to 37 µmol h1 g1. Prolonged exposureto darkness (ID plants) also lowered net uptake of NO3and NH4+ by, respectively, 86% and 95% of IL levels. For NH4+this was characterized by a large decrease in influx and a smalldecrease in efflux; whilst for NO3 the effect of a largedecrease in influx was reinforced by a smaller increase in efflux. The data were used to estimate the translocatory fluxes of NO3(0320µmol h1 g1) and NH4+ (0030.4µmolh1 g1), assimilation in the roots of NO3(0226µmol h1 g1) and NH+4 (0589 µmolh1 g1), and the concentrations of NO3 (915mol m3) in the cytoplasmic compartment of the roots.The relevance of variable influx and efflux to models for theregulation of N uptake is discussed. Key words: Lolium multiflorum, Trifolium repens, influx, efflux, nitrate, ammonium, 13N 相似文献
19.
Control of Wheat Root Elongation Growth: I. EFFECTS OF IONS ON GROWTH RATE, WALL RHEOLOGY AND CELL WATER RELATIONS 总被引:2,自引:0,他引:2
Pritchard, J., Tomos, A. D. and Wyn Jones, R. G. 1987. Controlof wheat root elongation growth. I. Effects of ions on growthrate, wall rheology and cell water relations.J. exp.Bot. 38: 948959. The nature of the ions in the bathing medium of hydroponicallygrown wheat seedlings strongly influenced root growth rate.In 0·5 mol m3 CaSO4 the growth rate was 32 mm24 h1 (used as 100% control rate). K+ and SO ions(10 mol m3) each inhibited extension growth (to about40% and 70% of the control value respectively). In the absenceof K+, Cl greatly reduced the inhibition due to SO42.Measurement of tissue plasticity and elasticity in the expandingzone with an Instron-type tensiometer indicated that both werea function of growth rate although relationship of plasticityto growth rate was the steeper and the more pronounced. Turgor pressure at the proximal end of the expanding zone wasnot correlated to growth, being approximately 0·65 MPain all treatments. In mature tissue turgor pressure varied withtreatment, but was also not related to growth rate. Cell membranehydraulic conductivity (5 x 107 ± 1·3 (10)m s1 MPa2) was not influenced by the presenceof K+. We propose that K+ and SO42 influence root growthrates by modulating the rheological properties of the wallsof the expanding cell. The physiological significance of these properties is discussed. Key words: Growth, wall extensibility, turgor pressure, wheat roots 相似文献
20.
Effects of Anoxia on Wheat Seedlings: I. INTERACTION BETWEEN ANOXIA AND OTHER ENVIRONMENTAL FACTORS 总被引:7,自引:1,他引:6
WATERS I.; KUIPER P. J. C.; WATKIN E.; GREENWAY H. 《Journal of experimental botany》1991,42(11):1427-1435
Anoxia was imposed on 46-d-old, intact wheat seedlings,after the roots had first been exposed for 1 d to O2 concentrationsbetween 0·016 and 0·06 mol m3. Apices ofthe main axis of the seminal roots were considered to have toleratedanoxia if elongation occurred after return from anoxia to air,hereafter called retention of elongation potential.During anoxia, elongation potential was retained longer in rootsof intact seedlings than in 05 mm excised root tips suppliedwith 50 mol m3 glucose. In intact seedlings, elongation potential was retained longerat 15°C than at 25°C, and at pH 50 and 60 than at pH40. These differences between treatments were maintained inthe presence of exogenous glucose, and glucose supply prolongedthe retention of elongation potential in all anoxic treatments. Elongation potential was retained much longer at very low 02concentrations (0006 to 00l mol m3) than under anoxia;this was established at pH 40. Anoxia inhibited the transport of sugars from the shoots and/orendosperm to the root by 79-97%, as assessed from experimentswith roots of intact plants exposed to anoxia at pH 60 and 15°C. Overall, the results demonstrate: (i) that the occurrence ofadverse effects of anoxia during waterlogging in the field mayinteract with other environmental factors and (ii) that thereare pronounced difficulties integrating data on tolerance toanoxia obtained in different laboratories. Key words: Anoxia, wheat seedlings, pH, temperature 相似文献