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1.
The effect of radiation from P32 on the growth and phosphateabsorption of barley seedlings was studied in water culture.Concentrations of carrier phosphate ranging from less than 001to 31 p.p.m. P were employed for varying periods. Between experiments wide variations occurred in the nature andextent of the effects of radiation. An increase in the proportionof the absorbed phosphate translocated to the shoots, and thereduction of root weight, were the most consistent symptoms.While severe injury was characterized by a reduction in bothgrowth and phosphate absorption, intermediate levels of P32on occasion caused increases in dry weight, in nutrient absorption,and in the development of lateral meristems. The interrelation of the observed effects of radiation is discussed;the reduced metabolic activity of root meristems is consideredto be the primary effect in the syndrome of radiation injury.Although injury is due to the accumulation of P32 in meristematicregions, no close correlation can be shown between its extentand the level of radiation received by the meristems. The inaccuracyof present methods for estimating the levels of radiation towhich tissues are exposed has complicated the investigationsof this subject. It appears, however, that the injurious levelof radiation may vary from under 10 to over 40 rep. per daywhen the treatment period is 5 to 7 days. If active accumulationof phosphate occurs, the meristems of plant roots may receivethis dosage when treated with more than 5 µ C. of P32per litre for periods of 6 days. The extent to which the effects of radiation may complicatethe interpretation of the results of plant physiological investigationsis considered. 相似文献
2.
The effect of the external concentration on the distributionof phosphate absorbed by young barley plants was studied inexperimental periods varying from 1 hour to 7days.The experimentalwere carried out in water culture with radioactive phosphorusas a tracer. The concentration of labelled phosphate suppliedto the plants ranged from 0·0003 to over 30 p.p.m. P. When the external concentration of phosphate is reduced below10 p.p.m. P, the proportion of the absorbed phosphate foundin the shoots is markedly reduced. Plants which have been treatedwith low concentrations of phosphate lose recently absorbedphosphate to the outer medium when transferred to phosphate-freesolutions. Plants treated with higher concentrations lose asmaller proportion of recently absorbed phosphate. Different balances of other nutrients do not affect the generalrelationship between the absorption and distribution of phosphate,though quantitative changes occur.It is concluded that the retentionof phosphate in the roots induced by dilute media is a directconsequence of the small quantity of phosphate entering theroots and is not attributable to the effects of other ions whichmay be simultaneously absorbed. 相似文献
3.
The Absorption and Utilization of Phosphate by Young Barley Plants: IV. THE INITIAL STAGES OF PHOSPHATE METABOLISM IN ROOTS 总被引:2,自引:0,他引:2
Organic phosphorus compounds have been extracted from the rootsof intact plants which have absorbed radioactive phosphate.The distribution of phosphorus between different organic fractionsof the root during a 24-hour absorption period is markedly influencedby the concentration of phosphorus supplied. Less than 1 minute after entry a significant proportion of theabsorbed phosphorus is found to be in organic compounds. Incorporationinto nucleotides is particularly rapid, whereas incorporationinto hexose phosphates occurs more slowly. The pattern of esterificationis influenced by the phosphate status of the plants. 2: 4-dinitrophenol (104M.) reduces the uptake of phosphorusand also the extent of esterification, the latter effect beingdue solely to reduced incorporation into the nucleotide fraction. Although extensive esterification of phosphate occurs in roots,it appears to be transported to the shoot as inorganic phosphateaccompanied by only a small amount of a single organic compound. 相似文献
4.
Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transportand the effects of acetic acid in white clover. I. Phosphateabsorption.J. exp. Bot. 39: 7988. The effect of acetic acid on phosphate absorption by white clovertissue has been examined. At 1·0 mol m3 acetic acid phosphateabsorption by roots of intact plants was stimulated by 36% (P< 0.001). At 5.0 and 10 mol m3 acetic acid there wasmarked inhibition of absorption by both suspension culturesof cells and the roots of intact plants. The inhibition waspH dependent with decreasing pH causing increased inhibition.Acetic acid caused changes in the membrane electropotential(E) with concentrations of 2·0 mol m3 or lesscausing persistent polarization whereas at 5·0 mol m3and higher concentrations the polarization was followed by agreater depolarization. Intracellular pH as measured by thefluorescence of fluorescein was lowered by acetic acid. Calculationsindicate that for white clover roots the proton motive force(pmf) appears to provide sufficient energy for phosphate absorption.It is proposed that acetic acid influences phosphate absorptionthrough its dependence on proton cotransport and that changesin J E affect the rate of phosphate absorption because of thedependence of the pmf on E. Key words: Phosphate absorption, intracellular pH, acetic acid, proton motive force, Trifolium repens, membrane electropotential 相似文献
5.
Responses to a localized supply of phosphate were studied inbarley grown in continuous flow solution culture. Root systemswere either uniformly supplied with 50 µM phosphate (controls)or the same solution was supplied to only a 4 cm or 2 cm lengthof a seminal root (localized supply), the remainder of the rootsystem receiving a nutrient solution lacking phosphate. Little development of laterals occurred on those parts of theroot system receiving no phosphate from the external solution,while an increase in the number and extension of laterals tookplace in the 4 cm zone enriched with phosphate. Compared withsimilar zones on controls, the total length of laterals wasincreased 15-fold in 21 d plants. In addition, rates of 32P-phosphateuptake and translocation to shoots per unit root weight werehigher than in controls by a factor of 2?55?0. Furtherincreases in the growth of lateral roots, and rates of phosphateuptake, were induced when the segment initially supplied withphosphate was restricted to only 2 cm. These localized modifications to root growth and uptake of phosphatelargely compensated for the deficient supply of phosphate tothe remainder of the root system. After an early period of retardedgrowth and phosphate stress, the relative growth rate of plantsand the concentration of phosphate in shoots were restored tolevels similar to that of the controls. The manner in which the supply of phosphate may control rootdevelopment, and the nature of the co-ordination between rootgrowth, phosphate uptake, and shoot growth, are discussed. 相似文献
6.
Breeze, V. G. and Hopper, M. J. 1987. The uptake of phosphateby plants from flowing nutrient solution. IV. Effect of phosphateconcentration on the growth of Trifolium repens L. suppliedwith nitrate, or dependent upon symbiotically fixed nitrogen.J.exp. Bot. 38: 618630. Nodulated white clover plants were subjected to a range of phosphateconcentrations in flowing solution culture (0.32 to 8.0 mmolm3 P) at 41 d from sowing, either supplied with nitrateor dependent on symbiotically-fixed nitrogen. No effect of phosphateconcentration in solution on dry matter production, relativegrowth rate, root/shoot ratio, or water soluble carbohydrateconcentration of the plant tissue was observed after 24 d fromthe start of the experiment, although the plants supplied withnitrate yielded more than the others. Phosphate uptake throughoutthe experimental period was related to the solution concentration,but the source of nitrogen did not affect the phosphorus concentrationsof the shoots. However, the roots of the plants dependent onsymbiotically-fixed nitrogen had higher concentrations of phosphorusthan those supplied with nitrate, but this did not appear tobe due to an increased phosphorus requirement for nitrogen fixation,because the amount fixed was unaffected by the phosphate concentrationin solution. The cation-anion balance showed that plants dependenton nitrogen fixation had no larger requirement for calcium thanplants supplied with nitrate, but a requirement for hydroxylions equivalent to over 130 kg lime per tonne of dry shoot.It is suggested that the enhanced phosphate uptake by plantsdependent on nitrogen fixation is due to this need for a cation-chargebalancing anion. Key words: Phosphate uptake, nitrogen fixation, Trifolium repens L., repens L., cation-anion balance, flowing solution culture 相似文献
7.
The absorption of phosphate by young barley plants was studiedusing a series of solutions ranging in concentration from 00003to over 30 p.p.m. P. The duration of most of the experimentswas 24 hours. The relationship between the external concentrationand absorption was found to be sigmoid, the slope of the curvebeing maximal when the external concentration was in the rangeof 01 to 03 p.p.m. P. It was concluded that the reductionin the slope of the curve, when the external concentration wasreduced below 01 p.p.m. P was due to an increasing fractionof the phosphate which entered the plants being retained inmetabolic systems in the root, from which it was subsequentlyreleased and returned to the outer medium. These results indicatethat when the external concentration was lowered below 01 p.p.m.P the plants absorbed progressively decreasing fractions ofthe nutrient available to them. The significance of this fromthe viewpoint of the growth of plants under the condition ofphosphate shortage is discussed. 相似文献
8.
Perennial ryegrass (Lolium perenne L.) was grown from seed for29 d in flowing solution culture containing 0.1, 0.4 or 6.4mmol m3 P before the concentrations were changed (0.1and 0.4 raised to 6.4; 6.4 lowered to 0.4; controls unchanged)for an experimental period of two weeks to test the hypothesisthat after the seedling stage, the maximum rate of plant growthcould be sustained by a lower concentration of phosphate atthe root/solution interface than was necessary for the maximumrate of seedling growth. During the 29 d seedling period growthwas greatest on 6.4 mmol m3 P achieving 179 mg per plantdry weight compared with 122 and 26 mg on 0.4 and 0.1 mmol m3P respectively. During the experimental period growth on thetreatment 6.4 lowered to 0.4 mmol m3 P continued at thesame rate as the 6.4 control achieving 981 and 983 mg per plantdry weight respectively. Similarly growth of the treatment 0.4raised to 6.4 mol m3 P was unaffected by the change inconcentration and was comparable with the 0.4 control. Bothresults support the hypothesis for seedlings exceeding about100 mg per plant dry weight. In contrast the small plants ofthe treatment 0.1 raised to 6.4 mmol m3 P behaved similarlyto seedlings and responded rapidly to the increased concentrationof phosphate in solution, achieving high rates of phosphateuptake and increasing the growth of shoot more than the growthof root so that the ratio of root: shoot declined from 065 to0.34, a value similar to that for the seedlings grown on 6.4mmol m3 P. Key words: Lolium perenne L, Phosphate concentration, Seedling growth 相似文献
9.
Maize plants were grown in nutrient solution without phosphate,or in which inorganic phosphate (Pi) was maintained at nearlyconstant concentrations of 1 µM, 10µM or 0·5mM. In vivo 31P-NMR measurements showed that there was no discernibledifference in the cytoplasmic Pi content (µmol cm3root volume) of the mature roots of plants exposed to 1 µM,10µM or 0·5 mM external phosphate for up to 12d. However, the vacuolar Pi content of the mature roots variedabout 10-fold between these three groups. The cytoplasmic Pi content of roots receiving no external phosphatedecreased significantly after about 7 d total growth, and atabout this time the vacuolar pool of Pi became too small foraccurate measurement. The presence of 1 µM Pi in the nutrientsolution completely prevented this decline in cytoplasmic Pi,and there was some evidence that it also raised the Pi contentof the root vacuoles above the almost undetectable level foundin the totally P-starved roots. During the first 79 d of growth, the nucleoside triphosphatecontent of the mature roots was unaffected by the concentrationof phosphate in the nutrient solution. The results highlight the close control of cytoplasmic concentrationsof certain important phosphorus metabolites in roots growingin soil of normal agricultural fertility. Key words: Vacuole, cytoplasm, intracellular compartmentation, NTP, P-nutrition 相似文献
10.
BREEZE V. G.; WILD A.; HOPPER M. J.; JONES L. H. P. 《Journal of experimental botany》1984,35(8):1210-1221
The effect of phosphate concentration in flowing solution cultureat a range between 0.04 and 32 mmol m3 P on the growthof perennial ryegrass was studied in two experiments, each lastingabout 45 d after sowing. Phosphorus contents of seedlings wereaffected by the concentration in solution within about 5 d fromgermination, and dry weight differences were first observedat about 6 d after this. The rate of uptake of phosphate byseedlings was affected by the concentration in solution beforethe root fresh weight or root/emdash shoot ratio had changed.Young plants (less than 4 weeks old) were more sensitive tophosphate concentration in solution than older ones. In conditionsof high rate of growth, older plants required a solution concentrationbetween 0.1 and 0.4 mmol m3 P to achieve maximum potentialgrowth rate, whereas for plants of similar age but less dryweight, 0.04 mmol m3 P was adequate. Towards the endof the experimental period, plants growing at a nominal solutionconcentration of 0.04 mmol m3 P were able to obtain phosphatefrom a solution of about 0.01 mmol m3P. Phosphate toxicity was not observed, nor were there visual symptoms(other than reduced growth) of phosphate deficiency in plantswhose growth was limited by phosphate concentration in solution. Key words: Lolium perenne, Phosphate uptake 相似文献
11.
The uptake of phosphate by barley plants grown under sterileand non-sterile conditions has been compared from solutionsranging in concentration between 0.001 to 10.0 ppm P. If specialprecautions are not taken to exclude microorganisms their activityon or in plant roots greatly modifies the absorption and utilizationof phosphate in plants, especially when the external concentrationis low. More phosphate is incorporated into nucleic acids, phospholipids,and phosphoproteins in the roots; at 0.001 ppm P these compoundsaccount for over 60 per cent of the phosphate absorbed comparedwith about 15 per cent in plants grown under sterile conditionsand even at 1.0 ppm P there is a twofold difference. The immobilizationof phosphate in the roots reduces its transfer to the shoots;at 0.001 ppm P, 2 as compared with 20 per cent of the phosphateabsorbed is transferred to the shoots. This effect decreaseswith increasing concentration but small differences are stillapparent up to about 0.5 ppm P. A further effect of micro-organisms is apparent when plantsare transferred from dilute solutions to phosphate-free solutions.Under non-sterile conditons there is an almost tenfold increasein the loss to these solutions of previously absorbed phosphate. It is evident that conclusions on the mechanism of absorptionof phosphate, based on experiments in which the actions of micro-organismshave been ignored, require reinvestigation. 相似文献
12.
The absorption and distribution of Cu in red clover (Trifoliumpratense L.) were measured in plants grown in flowing solutionculture with Cu maintained throughout at 0.5 µg 11and N supplied either as nitrate or through symbiotic fixation.Although there was a decrease in Cu absorption, both with time,and with a depleted nitrate supply, it increased to its formerrate when nitrate was adjusted to 10 mg N 11 after aperiod of depletion. Differences in absorption between plantsdependent upon fixation and those supplied with nitrate wererelated to the slower initial growth of the plants fixing N.Considerable proportions (> 30 per cent) of the absorbedCu were retained by the roots. At the final harvest, and withthe exception of plants grown with nitrate adjusted to 0.1 mgN 11 after a period of depletion, the proportion of theCu retained was related to the concentration of N in the roots.The different N treatments produced differences in Cu concentrationin the shoots, and the effects were greater in the youngestfully expanded leaves than in older leaves. Trifolium pratense L., red clover, absorption, copper, flowing solution culture, nitrogen 相似文献
13.
Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: IV. TRANSLOCATION AND REMOBILIZATION OF NITROGEN 总被引:1,自引:0,他引:1
Barley (Hordeum vulgare L., cvs Golf and Laevigatum) was grownunder nitrogen limitation in solution culture until near maturity.Three different nitrogen addition regimes were used: in theHN culture, the relative rate of nitrate-N additionwas 0·08 d1 until day 48 and then stepwise decreasedto, finally, 0·005 d1 during late grain-filling;the LN culture received 45% of the nitrogen addedin HN; the CN culture was maintained at RA 0·0375d1 throughout growth. At four different growth stages(vegetative,anthesis, and twice during grain-filling), 15N-nitrate was fedto the plants. In some cases (split root cultures),label was fed only to one-half of the root system. These wereharvested directly after labelling, whereas standardcultured plants were harvested at termination of theexperiment (day 148). Absorption of added nitrate was nearlycomplete in the HN and LN cultures, and translocation of nitrogenwithin the plants could thus be studied independently of differencesin nitrate absorption. Cycling of nitrogen absorbed by vegetativeplants accounted for up to 50% of the nitrogen recovered inthe roots. The sink strength of the roots for cycling nitrogen,however, declined during post-anthesis growth, and net lossof nitrogen from both roots and vegetative shoot tissue occurredconcomitantly with incorporation of labelled 15N-nitrogen. Thenitrogen of the vegetative shoot tissue was substantially lesslabelled than the nitrogen entering the ears, indicating thattranslocation of recently absorbed nitrogen to ears occurs withminor prior exchange with the bulk nitrogen of shoots. In caseswhere the sink strength of the ears was weak, as in LN-culturedLaevigatum (due to high frequency of sterile flowers) and inCN-cultured Golf, nitrogen translocated from roots appearedto be incorporated into the vegetative shoot tissue. There werealso indications that a fraction of the remobilized nitrogenwas actually lost from the plants in these cases. It is concludedthat the root remains efficient in translocation of nitrogento the aerial parts throughout ontogeny and that nitrogen takenup during grainfilling is preferentially directly translocatedto the developing grains. The further translocation of nitrogenreceived by vegetative shoot parts to ears appears mainly relatedto the potential of the ear to accumulate nitrogen. Nitrogenabsorbed/remobilized in excess of the sink strength of the earsis either invested in continued shoot growth, or is irreversiblylost from the plants. Key words: Barley, 15N-labelling, post-anthesis, remobilization, translocation 相似文献
14.
报道了海马齿(Sesuvium portulacastrum)对重金属汞的耐性和吸附特性。 在10 μmol·L-1汞胁迫时, 海马齿中脯氨酸含量明显低于对照; 丙二醛(MDA)含量、根的电解质外渗率(Electrolyte leakage rate, ELR)无明显变化; 叶绿素含量增加; 植物生长良好, 形态、生长速率、鲜重和根的长度与对照无区别, 且有新的须根形成。结果表明: 低浓度汞对海马齿的生长发育起着促进作用。海马齿能大量吸附积累汞离子, 主要积累在根组织中。当培养液中汞浓度为50 μmol·L-1时, 海马齿根中汞含量最高可达到33.9 μg·g-1DW, 是相同处理下地上部分的70倍。培养液中汞浓度为10 μmol·L-1时, 植物并未受到伤害, 且能快速生长, 此时根部的汞含量可达到12.02 μg·g-1 DW。由此可见, 海马齿植物表现为很强的耐汞和吸收汞特性。 相似文献
15.
Investigations of Carbon Transport in Plants: II. THE EFFECTS OF LIGHT AND DARKNESS AND SINK ACTIVITY ON TRANSLOCATION 总被引:4,自引:0,他引:4
The use of 11C as a tracer has allowed repetitive measurementsof the speed of assimilate translocation to be made on singlemaize plants throughout prolonged periods of light and darkness.The speed appeared to double when the light was switched on.The time required to achieve a maximum speed, usually about3·5 cm min1, depended on the duration of the previousdark period. When the plant was transferred to darkness thespeed immediately decreased by about 20 per cent and continuedto decrease over the next 20 h to values of 0·5 to 0·9cm min1. The mean speed of translocation in tomato in the light, andother C3 plants, was usually about 1 cm min1. It wasreduced by 1530 per cent when the fruit was removed orcooled from 26 to 10°C. 相似文献
16.
MATTSSON M.; LUNDBORG T.; LARSSON M.; LARSSON C.-M. 《Journal of experimental botany》1992,43(1):25-30
Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the HN culture the relative rate of nitrate-Naddition (RA) was 0·08 d1 until day 48 and thendecreased stepwise to, finally, 0·005 d1 duringgrain-filling; the LN culture received 45% ofthe nitrogen added in HN; the CN culture was maintainedat RA 0·0375 d1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m3external nitrate. Vmax (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative Vmax (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·32·3d1 during vegetative growth to 0·10·7d1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative Vmax can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative Vmax and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, Vmax 相似文献
17.
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
18.
菌根真菌在红壤中对柑桔吸收磷肥的研究 总被引:2,自引:0,他引:2
接种一种球囊霉 Glomus sp.编号 CC-1于红壤中,使酸桔和枳实生苗的根系感染形成泡囊丛枝内生菌根。应用放射性同位素~(32)P 标记的可溶性磷肥和难溶性磷肥来研究菌根真菌对柑桔吸收磷肥的作用。放射性宏观自显影和显微自显影表明菌根真菌加强了柑桔对两类磷肥的吸收。放射性测量和化学分析证明有菌根柑桔实生苗的地上部含磷量以及从红壤中和从肥料中吸收的磷量比无菌根的增多,有菌根实生苗的生长反应也较好。 相似文献
19.
Uptake of Phosphate by White Clover: II. THE EFFECT OF PH ON THE ELECTROGENIC PHOSPHATE PUMP 总被引:1,自引:0,他引:1
The effect of pH on the electrogenic phosphate pump in whiteclover roots was investigated. It was found that the pump operatedbetween pH 3.5 and 8.0 with an optimum at 4.3. External pH changesaffected phosphate uptake and PD to the same extent so thata constant relationship between them was maintained. The activityof the pump declined when the carbohydrate supply was cut offby excision of the root or defoliation of the plant but couldbe restored by lowering the pH around the root. It was concludedthat the electrogenic phosphate pump could be driven by a pHgradient across the cell membrane. However, there did not appearto be a direct relationship between the operation of the pumpand extrusion of H+ by the root. 相似文献
20.
The short-lived radio-isotope nitrogen-13 (half-life 10 min)was used as a tracer in studying fluxes of N in the roots ofintact barley plants. After supplying the plants with 13N-nitratefor 30 min, efflux of 13N into an unlabelled (wash) solutionwas followed under steady-state conditions for a further 10min. Tests with ion exchange resins suggested that all of the13N released during this period was in the form of nitrate. In addition to nitrate from a surface film of solution and fromthe free space of the roots, efflux from another compartmentwas detected, tentatively identified as the cytoplasmic nitratepool. In plants grown with nitrate as the only external N-source,efflux from this compartment decreased with a rate constantabout 0·17 min1 (half-time 4 min). Adding ammoniumsulphate to the wash solution alone did not significantly affecteither the initial rate, or the rate constant, of efflux of13N from these roots. However, 13N efflux decreased more rapidly(rate constant about 0·32 min1, half-time 2·2min) in roots grown in, and subsequently washed with, solutioncontaining ammonium nitrate. In barley plants grown with 1·5 mol m3 nitrate,the cytoplasmic nitrate pool was estimated to contain about2% of the total nitrate in the roots, corresponding to a cytoplasmicnitrate concentration 26 mol m3. Nitrate efflux was equivalentto almost 40% of nitrate influx in the roots of these plants. Key words: Ion transport, nitrate, ammonium, efflux analysis, compartmentation 相似文献