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1.
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
2.
Ritchie Raymond J.; Trautman Donelle A.; Larkum A.W.D. 《Plant & cell physiology》1997,38(11):1232-1241
Phosphate uptake rates in Synechococcus R-2 in BG-11 media (anitrate-based medium, not phosphate limited) were measured usingcells grown semi-continuously and in continuous culture. Netuptake of phosphate is proportional to external concentration.Growing cells at pHo 10 have a net uptake rate of about 600pmol m2 s1 phosphate, but the isotopic flux for32P phosphate was about 4 nmol m2 s1. There appearsto be a constitutive over-capacity for phosphate uptake. TheKm and Vmax, of the saturable component were not significantlydifferent at pHo 7.5 and 10, hence the transport system probablyrecognizes both H2PO4and HPO24. The intracellularinorganic phosphate concentration is about 3 to 10 mol m3,but there is an intracellular polyphosphate store of about 400mol m3. Intracellular inorganic phosphate is 25 to 50kJ mol1 from electrochemical equilibrium in both thelight and dark and at pHo 7.5 and 10. Phosphate uptake is veryslow in the dark ( 100 pmol m2 s1) and is light-activated(pHo 7.51.3 nmol m2 s1, pHo 10600 pmol m2s1). Uptake has an irreversible requirement for Mg2+in the medium. Uptake in the light is strongly Na+-dependent.Phosphate uptake was negatively electrogenic (net negative chargetaken up when transporting phosphate) at pHo 7.5, but positivelyelectrogenic at pHo 10. This seems to exclude a sodium motiveforce driven mechanism. An ATP-driven phosphate uptake mechanismneeds to have a stoichiometry of one phosphate taken up perATP (1 PO4 in/ATP) to be thermodynamically possible under allthe conditions tested in the present study. (Received June 16, 1997; Accepted September 4, 1997) 相似文献
3.
Influx and Efflux of Phosphorus in Roots of Wheat Plants in Non-Growth-Limiting Concentrations of Phosphorus 总被引:5,自引:0,他引:5
The regulation of net phosphorus uptake was studied in wheatplants at ambient non-growth-limiting P-concentrations. Wheat(Triticum aestivum cv. Klein Atalaya) seedlings were grown fromgermination in culture solutions containing 0.05, 0.5 and 5.0mol m3 phosphate. Only small increments in plant P-concentrationand specific accumulation rate for phosphorus were found whenambient P-concentration was increased 100 times. P-influx, estimatedby 32P-uptake, was markedly greater with increased externalP-concentration, but only small changes in Vmax and no changesin Km were found. Indirect estimation of P-efflux in a time-courseof 32P-uptake, and direct P-efflux measurements in washout experiments indicated that P-efflux markedly increasedin higher ambient P-concentration. The increase in P-effluxalmost completely neutralized the higher P-influx observed in5.0 mol m3 relative to 0.05 mol m3 phosphate.It is postulated that in non-limiting P-concentration net P-uptakeis mainly controlled by P-efflux. Key words: Net P uptake, 32P, kinetic parameters 相似文献
4.
Anabaena PCC 7119 showed higher rates of phosphate uptake whencells were under P-starvation. Phosphate uptake was energy-dependentas indicated the decrease observed when assays were performedin the dark or in the presence of inhibitors of photosyntheticelectron transport, energy transfer and adenosine triphosphataseactivity. Phosphate uptake was stimulated by Na+ both in P-sufficientcells and P-starved cells. Li+ and K+ acted as partial analoguesfor Na+. The Na+-stimulation of phosphate uptake followed Michaelis-Mentenkinetics, half-saturation (K) of phosphate uptake was reachedwith a Na+ concentration of 212 µM. The absence of Na+reduced the rates of phosphate uptake at all phosphate concentrationsassayed (120 µM). The maximum uptake rates (Vmax)decreased from 658 nmol P (mg dry wt)-1 h-1 in the presenceof Na+ to 149 nmol P (mg dry wt)-1 h-1 in the absence of Na+.The absence of Na+ did not change significantly the concentrationof phosphate required to reach half-saturation (K) (3.01 µMin the presence of Na+ vs 3.21 µM in the absence of Na+).In the presence of Na+ the rate of phosphate uptake was affectedby the pH; optimal rates were observed at pH 8. In the absenceof Na+ phosphate uptake was not affected by the pH; low rateswere observed in all cases. Monensin, an ionophore which collapsesNa+-gradients, reduced the rate of phosphate uptake in Na+-supplementedcells. These results indicated the existence of a Na+-dependentphosphate uptake in Anabaena PCC 7119. (Received September 8, 1992; Accepted November 17, 1992) 相似文献
5.
Young plants of Banksia hookeriana were grown in acid-washedsand with adequate phosphate and water supply, and a proportionwere inoculated with Phytophthora cinnamomi. There were no majordifferences in growth between uninoculated and infected plants,but there was a large increase in uptake of 32P with increasingroot disease. In healthy plants 32P uptake was greatest in youngleaf tissue, but in diseased plants labelled phosphate was directedmore towards older leaves where the activity was almost twicethat of young leaves. Enhanced uptake with disease was ascribed to possible blockageof the message or signal of phosphatetranslocation from shoot to root, such that the diseased rootincorrectly treated the shoot as P deficient and increased Puptake. Key words: Banksia hookeriana, Proteaceae, 32P uptake, Phytophthora cinnamomi 相似文献
6.
From compartmental analysis of 32P elution measurements, concentrationsand fluxes of phosphate were estimated for root cortical cellsof intact Lolium perenne L. plants, when in complete nutrientsolution containing 0.1 mol m3 phosphate with and without37 mmol m3 Al during loading and elution. Failure ofthe data, when plotted as ct. min1 remaining in the tissueas a function of time, to meet the criteria for first orderkinetics led to a discussion of the relative importance of transportto the shoot, assimilation, and complexation in the vacuole,in causing this discrepancy. It was concluded that complexationwas the most important factor. Transformation of the data tomeet the criteria for first order kinetics gave corrected valuesfor compartmental concentrations and fluxes of phosphate, andestimates of the size of the otherwise unresolved slowly exchangingcompartment within the vacuole equated with condensed phosphate.In the control this was 2.5 mol m3 P but in Al treatmentsa much larger amount of phosphate was complexed with Al (6.5mol m3 P). Phosphate transport to the shoot was unaffectedby Al. Instead, levels of Al, common in solution in upland soils,sequestered in the root vacuoles quantities of phosphate significantfor stressing the phosphate economy of nutrient-poor grassland. Key words: Lolium perenne L. phosphate, aluminium, compartmentation, complexation 相似文献
7.
The effect of ringing the stem on the electrical potential difference(PD) in the root cortical cells of H. annuus was studied. PDand salt transport were followed simultaneously. By ringingit was possible to separate the PD from K+, , and Cl uptake and H+ efflux. The uptake of phosphatehowever was found to be closely connected with a component ofthe PD. It was concluded that there is an electrogenic pumpfor phosphate in these roots which generates 6080 mV. 相似文献
8.
The effect of Na+ on phosphate uptake was studied in four strainsof cyanobacteria: Synechococcus PCC 7942, Gloeothece PCC 6501,Phormidium sp. and Chlorogloeopsis PCC 6912. Phosphate uptakewas stimulated by Na+ in all cases. Li+ and K+ acted as partialanalogues for Na+. Half-saturation [K1/2(Na+)] of phosphateuptake was reached with Na+ concentrations ranging from 317µM in Chlorogloeopsis to 659 µM in Phormidium. Theconcentration of phosphate required to reach half-saturationof phosphate uptake [K1/2(Pi)]was not changed by the presenceof Na+. (Received April 11, 1994; Accepted July 5, 1994) 相似文献
9.
Orthophosphate Absorption by the Sporophyte of Funaria Hygrometrica During Maturation 总被引:1,自引:0,他引:1
The absorption of phosphate by the sporophyte of Funaria hygrometrica,during its maturation, has been studied using 32P. More radioactivitywas found in the capsule when the absorption occured throughthe seta alone than when it look place through the leaves ofthe gametophyte. Each stage of capsule development studied isdescribed from transverse sections and electron micrographs.Phosphate is accumulated very actively by the capsule in theyoungest stage when the spores are being formed. The exchangesbetween the capsular tissues and the spores are low. 相似文献
10.
Apparent uptake and transport of H232PO4 from nutrientsolutions containing 100 mmol m3 phosphate were characterizedasfunctions of time, concentration and pH in ryegrass seedlings.On a log/log plot, concentration versus uptake to the root resolvedintotwo linear phases, suggesting a change in uptake mechanism orefflux at the break. These results were compared with thosefor 32P uptake and transport in solutions containing Al rangingfrom 0185 mmol m3. Al addition depressed pH, butbecauseuptake of P was unaffected by pH below 50, noadjustments were attempted. Uptake time-courses revealed clearlythe usualinitial adsorption shoulder in the uptake curve, increasingwith Al concentration up to 37 mmol m3. Beyond about2 h, P uptaketo the root became linear, at rates increasingwith external Al concentration up to 37 mmol m3. Concentrationsof Al muchabove 100 mmol m3 were toxic. Al treatmentsdid not affect P transport to the shoot and absorbed Al wasconfined to the root.The quantities of P and Al taken up intothe root indicated storage in cortex cell vacuoles, lockingup significant amounts of P.Experiments with tillering plantsshowed similar characteristics to those with seedlings. Sequesteringof P with Al within the rootcortex cells was evident, particularlyin plants which had been grown in nutrient containing Al fromsoon after germination. Aland P solution chemistry is discussedin the context of this work and the consequences of effectson P uptake for the economy ofphosphate poor upland soils wereconsidered. Key words: Phosphate, aluminium, adsorption, uptake, Lolium perenne L 相似文献
11.
Macklon A.E.S.; Lumsdon D.G.; Sim A.; McHardy W.J. 《Journal of experimental botany》1996,47(6):793-803
From compartmental analysis of 32P elution measurements, concentrationsand fluxes of orthophosphate were estimated for root corticalcells of intact seedlings of the indigenous grass Agrostis capillarisL. cv. Highland when in complete nutrient solution containing10 mmol m3 or 100 mmol m3 phosphate with or without3.7 and 37 mmol m3 Al, respectively, during loading andelution. When plotted as counts min1 remaining in thetissue as a function of time, the data failed to meet the criteriafor first order kinetics. Transformation of the data to meetthe kinetic criteria gave corrected values for compartmentalconcentrations and fluxes of phosphate, and estimates of theotherwise unresolved slowly exchanging compartment within thevacuole considered to be the cause of the discrepancy in fluxanalysis. In the control, the discrepancy was considered dueto sequestration of phosphate with Ca in the vacuole and a small,but not significant, increase in sequestered P occurred in thepresence of Al, the presence of which was confirmed by X-raymicroanalysis. A chemical speciation model was used to demonstrate,for various values of pH and carboxylic acid concentration,the possibility that phosphate was precipitated in root cellvacuoles as Ca and Al phosphates (hydroxy-apatite and variscite).The ecological significance of the ability of A. capillarisplants to make efficient use of scarce P resources by minimizingthe sequestration of P by Al in vacuoles, compared with Loliumperenne, was recognized. Key words: Phosphate sequestration, phosphate use efficiency, X-ray microanalysis, super-saturation 相似文献
12.
The rate of uptake of 32P from labelled NaH2PO4 solutions sprayedon to one leaf of swedes (Brassica napus) or French beans (Phaseolusvulgaris) was rapid during the first few hours and fell to zeroafter 4 days. 22P was detected in the root after 3 hours andcontinued to move out of the treated leaf for at least 6 daysafter application. A larger fraction of the applied 32P wasabsorbed from repeated than from a single spraying. Swedes absorbed more 32P from a single application to the lowersurface than to the upper surface of the leaf. Doubling theconcentration of the spray caused a small increase in the percentageof applied 22P that was absorbed. Absorption by French-beanleaves decreased slightly when the area sprayed with a constantamount of 32P was doubled, and decreased with increasing ageof leaf. Increasing the phosphorus supply to the roots of swedesaffected neither the initial rate nor the total amount of 32Puptake by the leaves but decreased the quantity of 32P thatwas translocated out of the treated leaf. Increasing the relative humidity of the air around the plantsalso increased32P uptake. Shading usually decreased uptake andalways decreased translocation. Rewetting the leaf to whichthe 32P had been applied, with water or sucrose solution, hadvariable effects. The significance of the results is discussed. 相似文献
13.
The acidophilic alga Dunaliella acidophila exhibits optimalgrowth at pH 1. We have investigated the regulation of phosphateuptake by this alga using tracer techniques and by performingintracellular phosphate measurements under different growthconditions including phosphate limitation. In batch culturewith 2·2 mol m3 phosphate in the medium the uptakeof phosphate at micromolar phosphate concentrations followeda linear time dependence in the range of minutes and rates werein the range of 1 µmol phosphate mg1 chl h1,only. However, under discontinuous phosphate-limited growthconditions, tracer influx revealed a biphasic pattern at micromolarphosphate concentrations: An initial burst phase resulted ina 104-fold internal phosphate accumulation and levelled offafter about 10 s. A double reciprocal plot of the initial influxrates obtained for phosphate-limited and unlimited algae exhibitedMichaelis-Menten kinetics. Phosphate limitation caused a significantactivation of the maximum velocity of uptake, yielding Vmaxup to 1 mmol mg1 chl h1 as compared to valuesin the order of 50 µmol phosphate mg1 chl h1for the second phase (this magnitude is also representativefor non-limited batch cultures). Concomitantly the Michaelisconstant was altered from 4 mmol m3 to 0·7 mmolm3. The rapid uptake of phosphate was inhibited by arsenateand FCCP and was not stimulated by Na+. The pH dependence oftracer accumulation and measurements of the intracellular phosphatepool under different growth conditions indicate that at lowpH and low external phosphate concentrations the high protongradient present under these conditions is utilized for a H3PO4uptake or a H+/H2PO4 cotransport. However, when the externalphosphate concentration was increased to levels sufficientlyhigh for transport to be driven by the positive membrane potential(10 mol m3 phosphate), the pH dependence of phosphateuptake was more complex, but could be explained by the uptakeof H3PO4 or a H+/H2PO4-cotransport at low pH and a differenttype H2PO4-transport (with unknown type of ion coupling)at high pH-values. It is suggested that this flexible couplingof phosphate transport is of essential importance for the acidresistance of Dunaliella acidophila. Key words: Acid resistance, Dunaliella acidophila, phosphate cotransport, phosphate limitation, plasma membrane, sodium 相似文献
14.
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
15.
Chalutz Edo; Mattoo Autar K.; Anderson James D.; Lieberman Morris 《Plant & cell physiology》1978,19(1):189-196
Inorganic phosphate regulated ethylene production in shake culturesof Penicillium digitatum. Decreasing the phosphate level ofthe medium from 100 to 0.01 mM markedly increased, about 100-fold,the rate of ethylene production, in 96 hr, which was confinedentirely to the fungal mycelium. Exogenous addition of between0.01 to 100 mM phosphate, to high ethylene producing, low-phosphatecultures strongly inhibited their ethylene production and increasedthe ATP content of the mycelium. Phosphate also inhibited ethyleneproduction in apple slices. Addition of calcium ions to theincubation medium stimulated the production of ethylene in appleslices, subhook epicotyl segments of pea and shake culturesof P. digitatum. We suggest that this stimulatory effect wascaused by the reduction of inhibitory levels of phosphate, whichcomplexed with calcium. Thus, phosphate in conjunction withcalcium may play an important role in regulating ethylene productionnot only in P. digitatum but also in higher plants.
1 On leave from the Agricultural Research Organization, TheVolcani Center, Israel.
2 On leave from the M.S. University of Baroda, India. (Received September 7, 1977; ) 相似文献
16.
Istvanovics Vera; Padisak Judit; Pettersson Kurt; Pierson Donald C. 《Journal of plankton research》1994,16(9):1167-1196
The thermal stratification in Lake Erken was short and relativelyunstable in 1989. Changes in the species composition of thephytoplankton between early May and August followed the generalsuccession pattern outlined for other temperate lakes. Fast-growing,r-strategist cryptophytes, dominant in the early phase of succession,could be separated sufficiently by 12 µm membrane filtersfrom larger K-strategists like Ceratium hirundinella and Gloeotrichiaechinulata which dominated in July. Under more turbulent conditions,the biomass of diatoms increased, and these species were also>12 µm. Growth rates of the phytoplankton and thoseof the two size groups were sensitive to the species composition,but fitted reasonably to the Droop model. Long turnover timesof orthophosphate in the water, the Phosphorus Deficiency Indicatordefined here as the ratio of the light-saturated rate of photosynthesisand the conductivity coefficient of phosphate uptake, and relativegrowth rates generally indicated low P-deficiency. Moderatedeficiency was observed in late July, towards the end of thestratification period. Steady-state net P-uptake rates werecalculated from the Droop model and compared with instantaneousnet P-uptake rates estimated from 32P uptake kinetics by thelinear force-flow relationship of Falkner et al. (Arch. Microbiol.,152, 353361, 1989). The two data sets showed surprisinglysimilar seasonal trends. Depletion of epilimnetic soluble reactivephosphorus (SRP) resulted in enhanced utilization of intracellularlystored P. Such periods were, however, interrupted by elevatedSRP inputs to the epilimnion that led to luxury P uptake anda low incidence of P deficiency. 相似文献
17.
Evaluation of Arsenate- and Vanadate-Associated Changes of Electrical Membrane Potential and Phosphate Transport in Lemna gibba G1 总被引:8,自引:0,他引:8
Interference of arsenate and vanadate with phosphate uptakein Lemna gibba L. was studied by measuring voltage changes and(32P)phosphate uptake. Arsenate proved to be competitive withthe high- and low-affinity phosphate uptake system. It inducedtransient membrane potential changes of up to 120 mV which weresimilar to those induced by phosphate and indicated a cotransportmechanism with at least 2H+/H2As. The amplitude of the transient arsenate-induced membrane depolarization wasstrongly influenced by phosphate starvation. A permanent membranedepolarization to the diffusion potential was achieved within2 to 6 h in P-starved plants. Thus, arsenate is indeed a stronglycompetitive physiological analogue of phosphate in higher plants. Vanadate was easily transported into L. gibba as concluded fromtransient Em changes of up to 110 mV. Vanadate interfered onlyslightly and non-specifically with the two phosphate transportmechanisms. Like phosphate, vanadate uptake seems to be an H+-cotransportmechanism, both with similar optima at pH 6.0. Unlike phosphateuptake, vanadate-linked membrane depolarization was not affectedby high intracellular phosphate concentrations. P-starvationdid not enhance the weak long-term effect on Em. Hence, vanadate,in contrast to arsenate, is not regarded as a physiologicalphosphate analogue. The distinct and rapid vanadate-inducedand permanent membrane depolarization of Avena sativa, Triticumaestivum and Glycine max leaves was not seen in Lemna nor inleaves of Gossypium hirsutum and Nicotiana tabacum. Plasmalemma-enrichedpreparations of L. gibba revealed, however, a high vanadate-sensitiveATPase activity (87%). As a possible explanation for these differencesit is suggested that the latter plant species have cytosolicvanadate-detoxifying properties, i.e. they can reduce vanadateto vanadyl ions, in contrast to the former group of plant species. Key words: Arsenate, vanadate, H+/solute cotransport, membrane potential, phosphate competition 相似文献
18.
Phosphate uptake rate and its incorporation into the foliarorgan of four crop plants, viz. pearl millet, pigeon pea, wheat,and gram, and six weeds Cyperus rotundus, Chenopodium album,Asphodelus tenuifolius, Anagallis arvensis, Vicia hirsuta, andEuphorbia dracunculoides were studied with the help of P32.It is concluded that phosphate uptake and its incorporationinto the leaves depend on age and species of plant. Rate ofphosphate uptake increases in all species as they proceed towardsmaturity but the incorporation of phosphate is maximum duringearly stages of growth. 相似文献
19.
Effects of Intermittent Desiccation on Nutrient Economy and Growth of Two Ecologically Contrasted Mosses 总被引:2,自引:0,他引:2
The mossesBrachythecium rutabulum (Hedw.) B., S. & G. andPseudoscleropodiumpurum (Hedw.) Fleisch. were cultivated for more than 50 d ina growth cabinet with or without weekly drying interludes of24 h. Some plants also received applications of a dilute NPKnutrient solution at weekly intervals. The continuously hydratedplants showed appreciably more biomass production than thosereceiving intermittent desiccation. Desiccation led to somebleaching of the green tissues inB. rutabulum but not inP. purumwhich appeared more desiccation-tolerant. NPK addition causeda further significant growth stimulation in continuously hydratedplants, but not in intermittently desiccatedB. rutabulum. Pseudoscleropodiumpurum showed NPK-induced growth stimulation even when intermittentlydesiccated. Net uptake of N was similar in desiccated and hydratedplants in both species. Considerable net uptake of P and K+occurredin continuously wetB. rutabulum , but uptake was much reducedin intermittently desiccated plants. Net uptake of P and K+byP.purum was similar in desiccated and hydrated samples. IntracellularK+, leaked from the cells during the desiccation treatment,was retained by cation exchange on the negatively charged cellwalls in both species. Levels of intracellular K+and Mg2+inthe new growth were maintained at the expense of the pool ofexchangeable cations. The growth stimulation and the net uptakeof nutrients under intermittent desiccation was greatest whenthe NPK application was made at the start of rehydration, possiblybecause of accentuated uptake in the early stages of recovery.The results support the hypothesis thatP. purum has a lowernutrient requirement thanB. rutabulum and highlight the importanceof continuous hydration for the latter's more productive plantlife strategy. The data also show that considerable new growthof bryophyte tissues is possible without additional nutrientabsorption. Brachythecium rutabulum ; Pseudoscleropodium purum ; mineral nutrition; desiccation; solute leakage; plant life strategies 相似文献
20.
Phosphate Uptake and Transport by Roots and Stolons of Intact White Clover (Trifolium repens L.) 总被引:1,自引:0,他引:1
The extent to which phosphate can be absorbed directly fromthe outer medium by stolon internodes and contribute to thetotal accumulation of phosphate by intact plants of white clover(Trifolium repens L. cv. Blanca) was assessed in hydroponicexperiments in a controlled environment room. The uptake ofphosphate by intact roots or stolons was measured by sealinga segment (6-0 mm long) across a flow-cell in which 32P-labellednutrient solution was circulated for 24 h, the rest of the rootsystem receiving unlabelled nutrient solution. The rate of uptakeof phosphate (µmol g1 d1 dry wt. basis)by roots was more than 300 times that by intact stolons. Pretreatmentof stolons by gentle abrasion to remove cuticle, so as to simulatethe condition of stolons in the field, increased the uptakeof phosphate 7-fold compared with that of intact stolons. However,the potential of stolons to contribute to the P status of whitedover in the field was calculated to be small (5%). When an incision was made through the hypodermal layer of stolons,the rate of phosphate uptake greatly increased, attaining 71%of that by root segments. This increase, which was greater athigher phosphate concentrations, indicates that the suberi.zedhypodermis constitutes a major barrier to the influx of phosphatein the stolon. After withholding phosphate for different time intervals, thesubsequent rate of phosphate uptake by roots was increased 2-3-foldafter 2 d phosphate deprivation and 3-4-fold after 6 d or 13d phosphate deprivation. A higher proportion of absorbed phosphatewas transported to shoots in phosphate-deprived plants. After1 d of uptake following restoration of the phosphate supply,the concentrations of labelled phosphate in shoots were greaterthan in control plants, although the concentrations of labelin roots was less. However, the rate of uptake of phosphateby stolons, following deprivation, was not significantly increased.These results suggest that the mechanism regulating the enhancedrate of phosphate loading into the xylem, initiated by a periodof phosphate deprivation, is specific to roots and is not inducedin stolons. The results are discussed in relation to the growth and acquisitionof phosphate by white clover in the field. Key words: Nutrient deficiency, phosphate, stolons, transport (ions), Trifolium repens 相似文献