Comparison of the Effects of Root Temperature on Nitrate and Ammonium Nutrition of Oilseed Rape (Brassica napus L.) in Flowing Solution Culture: I. GROWTH UPTAKE OF NITROGEN

Oilseed rape plants (Brassica napus L. cv. Bien venu) were grownin flowing nutrient solution and acclimatized over 49 d to lowroot temperature (5 ?C) prior to treatment at root temperaturesof 3, 7, 11 or 17?C for 14 d, with common air temperature of20/15?C day/night and solution pH 6.0. The effects of root temperatureon growth, uptake and assimilation of N were compared with Nsupplied either as or at 10 mmol m^–3. Plant fresh weight, dry weight and leafarea increased with root temperature. Q₁₀ values for specificgrowth rates between 7?C and 17?C were 1.10 and 1.33, respectively,under and nutrition. Fresh weight and leaf area were favoured by nutrition, particularly at 11 ?C and 17 ?C. At each temperaturethe net uptake of over 14 d was similar to that of , increasing 4-fold between 3?C and 17 ?C. Unit absorption rates of increased over the first 3 or 4 d, to an extent that increased with roottemperature. Thereafter, near constant values were maintainedat 3, 7 and 11 ?C. Unit absorption rates of at 3 ?C and 7 ?C did not increase over the first 3 or 4 d. Plantsat 17?C responded differently from those at other temperatures,with steep increases in unit absorption rates of and after day 8. The tendency for plants to adjust unit absorption rates of N over 14 d to become independentof root temperature was limited to the range 7–11 ?C.Q¹⁰ values between 7 ?C and 17 ?C for unit absorption rateswere 1.7—1.8 and 1.4—1.5, respectively, for and . Plants at 7, 11 and 17?C absorbed more than was subsequently assimilated, but at 3 ?C the absorption of was insufficient to meet the assimilatory demand. The results are discussed comparativelyfor and and in terms of the factors that determine unit absorption rates of N inresponse to a change in root temperature. Key words: Brassica napus, oilseed rape, root temperature, nitrate, ammonium, ion uptake rate     

Nitrate Uptake and Assimilation following Nitrate Deprivation

Upon first exposure to , the uptake and reduction capacities of dark-grown corn (Zea maysL.) roots are initially low, but increase markedly within 6h. The development of the accelerated uptake rate appears to be substrate ‘induced’ as is reductase (NR), the first enzyme in the assimilatory pathway. However, the ‘induction’of uptake is independent of NR induction. The effect of deprivation was studied to determine the role of endogenous on subsequent uptake and reduction. Corn roots were ‘induced’ for 24 h in 0–5 mol m^–3 nutrient solution and then exposed for 0 to 32 h to -free nutrient solution. Uptake and reduction of were determined periodically by exposing sets of roots to a1 h pulse of 0.5 mol m^–3 . Neither uptake (4.57 µmol root^–1 h^–1)nor the percentage of absorbed reduced (27%) was changed significantly (P 0.05) by exogenous deprivation. However, the estimated ‘induced’ componentof uptake decreased significantly (50% after 32 h). Concurrently, the ‘non-induced’ basal componentof uptake increased. Previously accumulated decreased from 23 to 4.5 µmol root^–1 after 32 h of exogenous deprivation. Nearly equivalent quantities of endogenous were used for translocation and reduction during deprivation. During each 1 h pulse, the amounts of translocation and net efflux of to the uptake solution were similar. Net efflux of was strongly correlated (r = 0.991) to the amount of endogenous . The remaining endogenous and its rate of utilization were apparently sufficient to minimize a rapid declineor complete loss in both the ‘induced’ uptake state and the rate of in vivo assimilation. Key words: reduction, translocation, efflux, root, Zea mays L     

Interactions Between the Uptake and Assimilation of Inorganic Nitrogen and Carbon in Amphidinium spp. (Dinophyceae)

The rate of exponential growth of Amphidinium carterae Hulburtwas the same (0.025 h^–1) with either or as sole N-source. Nevertheless, in short-term experiments, cells growing exponentially with as N-source took up added 5–6 times faster than . accumulated in the cells. Addition of inhibited, reversibly, disappearance of from the medium; prior N-deprivation of the cells did not affect this inhibition. N-repIetecells, grown with as N-source, took up for several hours both in light and darkness, butthe uptake by such cells soon ceased in darkness although it continued in light. When uptake ceased, the cells could still take up rapidly in darkness. Ammonium taken up was assimilated rapidly into organic-N includingglutamine, other amino acids and protein. Ammonium uptake in darkness was accompanied by the utilizationof cellular polysaccharide, mainly glucose polysaccharide. Mostof this carbon was unavailable for the dark assimilation of. Addition of the analogue, methylammonium, did not initiate polysacchande catabolism. Itis suggested that a control mechanism is in operation, througha product of assimilation, which operates on one or more of the enzymes concerned with polysaccharidebreakdown, for example, -amylase or phosphorylase. Uptake of was accompanied by a high rate of dark ¹⁴CO₂ fixation and with both Amphidintum klebsii Kof.et Swezy and A. carterae N-deprivation led to a marked increasein this rate following addition of ; addition of had much less effect. The possible implications of these findings for the eco-physiology of marine dinoflagellatesare discussed. Key words: Ammonium, nitrate, CO₂ fixation     

Expression of Characteristics of Ammonium Nutrition as Affected by pH of the Root Medium

To study the effect of root-zone pH on characteristic responsesof -fed plants, soybeans (Glycine max {L.}Merr. cv. Ransom) were grown in flowing solution culture for21 d on four sources of N (1.0 mol m^–3 , 0.67 mol m^–3 plus 0.33 mol m^–3, 0.33 mol m^–3 plus 0.67 mol m^–3 , and 1.0 mol m^–3) with nutrient solutions maintained at pH 6.0, 5.5, 5.0, and 4.5. Amino acid concentration increased inplants grown with as the sole source of N at all pH levels. Total amino acid concentration in the rootsof -fed plants was 8 to 10 times higher than in -fed plants, with asparagine accounting for more than 70% of the total in the roots of these plants.The concentration of soluble carbohydrates in the leaves of-fed plants was greater than that of -fed plants, but was lower in roots of -fed plants, regardless of pH. Starch concentration was only slightlyaffected by N source or root-zone pH. At all levels of pH tested,organic acid concentration in leaves was much lower when was the sole N source than when all or part of theN was supplied as . Plants grown with mixed plus N sources were generally intermediate between - and -fed plants. Thus, changes in tissue compositioncharacteristic of nutrition when root-zone pH was maintained at 4.5 and growth was reduced, still occurredwhen pH was maintained at 5.0 or above, where growth was notaffected. The changes were slightly greater at pH 4.5 than athigher pH levels. Key words: Ammonium, nitrogen nutrition, root-zone pH, soybean, tissue composition     

Effect of Nitrogen Form and Counterion on Establishment of the Rhizobium trifolii-Trifolium repens Symbiosis

The effect of level of different counterion forms of or or both, on establishment of the Rhizobium trifolii-Trifolium repens symbiosis was evaluatedin plants cultured under bacteriologically controlled conditions. Ammonium had little effect on nodule formation, and even after exhaustion there was little compensatory nodule formation. Plant growth, nodule mass and acetylene reductionactivity all declined with increasing levels of . Except for , different counterion forms had little effect on plant growth, nodule numberand mass, and acetylene reduction activity. Ammonium markedlydecreased pH, the extent being dependent upon level and counterion present. Nitrate inhibited nodulation while levels remained in excessof plant uptake. Compensatory nodulation followed exhaustionof or at lower or levels. Nodule mass and acetylene reduction activity decreased, but plant growth increased withincreasing or levels. Nitrate raised the pH of the nutrient solution by one unit orless. Different or counterion forms had little effect on the symbiosis or plant growth. Ammonium nitrate severely inhibited nodulation but on exhaustionmarked compensatory nodulation occurred. The patterns of nodulemass, acetylene reduction activity and plant growth with increasingNH₄NO₃ levels were similar to or alone. Plants provided with NH₄NO₃ or no nitrogenwere similar in only slightly decreasing pH. Key words: Ammonium, Nitrate, Ammonium nitrate, Nitrogen fixation, Rhizobium trifolii, Trifolium repens, Symbiosis establishment, Nodulation     

Cyclic Variations in Nitrogen Uptake Rate of Soybean Plants: Effects of External Nitrate Concentration

Net uptake of by non-nodulated soybean plants [Glycine max (L.) Merr.cv. Ransom] growing in flowing hydroponiccultures containing 0–5, 1.0 and 10-0 mol m^–3 was measured daily during a 24-d period of vegetativedevelopment to determine if amplitude of maximum and minimumrates of net uptake are responsive to external concentrations of . Removal of from the replenished solutions during each 24-h period was determinedby ion chromatography. Neither dry matter accumulation nor theperiodicity of oscillations in net uptakerate was altered bythe external concentrations. The maxima of the oscillations in net uptake rate, however, increased nearly3-fold in response to external concentrations. The maxima and minima, respectively, changed from 4.0 and 0–6mmol per gram root dry weight per day at an external solution level of 05 mol m^–3 to 15–2and -2–7 mmol per gram root dry weight per day at an external solution level of 10–0mol m^–3 . The negative values for minimum net uptake rate from10–0 mol m^–3 solutions show that net efflux was occurring andindicate thatthe magnitude of the efflux component of net uptake was responsiveto external concentration of . Key words: Nitrate uptake rate, carbon-nitrogen partitioning, flowing solution culture     

Influence of Inorganic Phosphate on Photosynthesis of Wheat Chloroplasts: I. PHOTOSYNTHESIS AND ASSIMILATE EXPORT AT 5 ?C AND 25 ?C

Chloroplasts were isolated from 10 d old wheat seedlings andilluminated at 5 ?C or 25 ?C in various concentrations of . Photosynthetic oxygen evolution, ATP content, andexport of triose phosphates and 3-phosphoglycerate were measured.Incorporation of ¹⁴C from NaH¹⁴CO₃ into pentose monophosphates,fructose monophosphate, and glucose monophosphates was determined. The ATP content in illuminated chloroplasts decreased when the concentration in the medium was low. The ATP content increased when the concentration was increased. A higher . concentration in the medium was needed to increase the ATP at 5 ?C than at 25?C. This would suggest that deficiency occurs more readily at low than at high temperatures. More ¹⁴C wasincorporated into photosynthetic metabolites within the chloroplastsat 5 ?C than at 25 ?C, indicating decreased assimilate exportwhen the temperature was low. Dihydroxyacetone phosphate waspreferentially exported when the concentration enabled a high rate of photosynthesis at 25 ?C. However, underconditions of deficiency, either due to low concentration in the medium or due to low temperature, 3-phosphoglycerate was preferred for export. The results suggest that the relatively high photosyntheticrates at low temperature are due to increased concentrationsof photosynthetic metabolites. The assimilate export at lowtemperature seems to be decreased due to decreased concentrationsof dihydroxyacetone phosphate in the stroma. Preferential exportof 3-phosphoglycerate at low temperature or at low concentration in the medium may be a consequence of high stromalconcentrations of this metabolite. On the other hand, it couldalso be due to decreased stromal pH. Key words: Chloroplast, Photosynthesis, Phosphate, Temperature, Translocation, ATP, Wheat     

Nitrate Nutrition of Grasses from Steady-State Supplies in Flowing Solution Culture following Nitrate Deprivation and/or Defoliation: I RECOVERY OF UPTAKE AND GROWTH AND THEIR INTERACTIONS

Two Lolium genotypes, i.e. Lolium perenne cv. S23 and a L. perenne? L. multiflorum hybrid cv. Augusta were, in one treatment,grown in flowing solution culture with a maintained supply of at 10 mmol m–3 throughout. In another treatment, the plants were deprived of for 11 d, was then re-supplied and both control and N-deprived plants were either defoliatedor left entire. Effects of the stresses imposed by N deprivationor defoliation on subsequent net uptake of , shoot and root growth and their interactions were examined.There were no major differences in the behaviour of the twogenotypes throughout. The removal of NO3 supply did not altertotal dry matter production during the 11 d period of deprivationbut the rate of root growth accelerated markedly. There waslittle effect of N deprivation on the specific growth ratesof the recovering defoliated shoots. Cumulative net uptake of closely paralleled the pattern of growth and there were obvious and marked effects of both N deprivationand defoliation. Effects on uptake were more distinctly demonstrated when uptake was expressed on aper unit root or shoot basis, i.e. specific unit absorptionrates (S_NO3). In the control plants with sustained supply, there was a progressive decline with time in S_NO3, inspite of an increasing shoot: root ratio. After both N deprivationand defoliation treatments there was a rapid initial increasein S_NO3, followed by an oscillatory cycle of increasing anddecreasing rates with a 10–11 d period. The relationshipsbetween growth and uptake were complex and did not conform to a previously predicted linear relationshipbetween S_NO3, and the ratio total fresh plant weight: root freshweight. The results are discussed in relation to the possiblemechanisms involved. It is suggested that the oscillations inunit absorption rate indicated that the roots of N-deprivedor defoliated plants retained a high capacity for absorptionimmediately after re-supply or defoliation and that the stressedplants were unable to assimilate or utilize taken up; net uptake then decreased through a shift in favourof efflux over influx until the influx mechanism was able todominate and the pattern was then repeated. Key words: Lolium, genotypes, N deprivation, nitrate uptake, defoliation, unit absorption, growth     

Differential rates of inhibition of N2 fixation by sustained low concentrations of NH4+ and NO3- in northern ecotypes of white clover (Trifolium repens L.)

An experimental study in flowing solution culture compared threeNorwegian ecotypes (from Saerheim, Pasvik and Bod) and a commercialcultivar (Ac51) of white clover (Trifolium repens L.) and demonstrateddifferences with respect to the rate and intensity with whichN₂ fixation was affected when or were supplied at 20 mmol m^–3 over 14 d. Plants were nodulated and N₂ fixation wasestablished over 17 d prior to supplying mineral N, with shoottemperature 25/15 C day/night and root temperature adjustedprogressively to 12C. Control plants received no mineral Nthroughout, and did not grow as rapidly as those supplied with or . Mineral N generally depressed the total N₂ fixation per plantrelative to control plants, with two exceptions. The effectof on N₂ fixation was moresevere than that of and, over the 14 d, -fed plants fixed more N₂ than the comparable -fed plants. Interpolated daily rates of N₂ fixation per plant andnodule dry wts were used to calculate specific rates of N₂ fixation.These showed that (1) addition of either or initially stimulated fixation relative to control plants and to mineral N uptake;(2) this stimulation was greatest and was delayed by 1-2 d in-fed plants; and (3) nutrition sustained higher residualrates of N₂ fixation after 8 d compared with nutrition, under which fixation all but ceased after10 d in three of the genotypes. Ecotype Bode showed by far themost severe induced depression of N₂ fixation. Key words: N₂ fixation, nitrate, ammonium, white clover, northern ecotypes     

An analysis of the physiological basis of commonality between diurnal patterns of NH4+, NO3- and K+ uptake by Phleum pratense and Festuca pratensis

Commonality in diurnal variation in net uptake of by the grasses Phleum pratense L. cv. Bodin (timothy),and Festuca pratensis Huds. cv. Salten (fescue) was evaluatedin flowing solution culture under a semi-natural light regime.Hourly uptake rates from constant 20 mmol m^–3 concentrationsof each ion were measured concurrently over 7 d, without physicaldisturbance. The light period was 11 h, natural light supplementedby constant artificial illumination, with a step-transitionto a 13 h dark period. Uptake of all three ions showed a broadlysimilar pattern of diurnal variation, rates increasing duringthe light period and decreasing during the darkness to a minimumwithin 2 h of the end of the dark period. The amplitude wasgreatest during high-irradiance days, and both proportionatelyand absolutely greater for (mean min:max uptake?0.24) than (min:max=0.41) or K⁺ (min:max?0.34). There were significantdifferences between and the other two ions whose behaviour coincided in almost all respects, in timing of maximum and minimumrates, and acceleration in uptake during the light period. Preferentialuptake of over increased sharply during the first half of the lightperiod; in relative terms uptake accelerated twice as fast as uptake. Fescue always absorbed more than but timothy showed a preference for during part of the dark period. The results are interpreted in terms ofthe hypothesis that diurnally fluctuating ‘sink-strength’for nutrients is the primary determinant of nutrient transportrates, although uptake may become temporarily uncoupled fromnutrient demand during periods of physiological stress or perturbation,such as towards the end of the dark period, during which uptakerates are determined by factors (e.g. carbohydrate supply) otherthan current nutrient demand. Key words: Ammonium, diurnal variation, Gramineae, ion uptake, nitrate, potassium, regulation     

Cyclic Variations in Nitrogen Uptake Rate in Soybean Plants: Uptake During Reproductive Growth

Net uptake of by non-nodulated soybean plants [Glycme max(L ) Merr cv Ransom] growing in flowing hydroponicculture was measured daily during a 63 d period of reproductivedevelopment between the first florally inductive photopenodand late seed growth Removal of from a replenished solution containing 10 mol m^– was determined by ion chromatography Uptake of continued throughout reproductive development The net uptakerate of cycled between maxima and minima with a periodicity of oscillation of 3 to 7 d during the floralstage and about 6 d during the fruiting stage. Coupled withincreasing concentrations of carbon and C:N ratios in tissues,the oscillations in net uptake rates of are evidence that the demand for carbohydrate by reproductiveorgans is contingent on the availability of nitrogen in theshoot pool rather than that the demand for nitrogen followsthe flux of carbohydrate into reproductive tissues. Key words: Nitrate uptake rate, carbon-nitrogen partitioning, Glycme max (L ) Merrill     

ATP Synthesis Coupled to Nitrate Photoreduction in the Alga Hydrodictyon africanum

The presence of exogenous stimulates O₂evolution in illuminated H. africanum cells at the CO₂ compensationpoint, and it is likely that reduction in the light uses reductant produced in non-cyclic electron flow.When sources of ATP other than fermentation are absent, thepresence of , light, and a functional non-cyclic electron transport pathway stimulates active, ATP-dependentH₂ influx. This is consistent with non-cyclic electron flow associated with reduction being coupled to ATP synthesis. This -dependent ATP synthesis may be quantitatively important as a source ofATP during photolithotrophic growth with as N source in H. africanum and other algal unicells.     

Relative Uptake Rates of Inorganic Nutrients by NO3- and NH4+ Grown Ricinus communis and by two Plantago Species

Allen, S., Thomas, G. E. and Raven, J. A. 1986. Relative uptakerates of inorganic nutrients by and grown Ricinus communis and by two Plantago species.—J. exp. Bot. 37: 419–428. The relative rates of uptake and assimilation of C, N, P, S,Cl^–, K⁺ , Na⁺ Ca²⁺ and Mg²⁺ by and grown Ricinus conimunisand by NH₄NO₃- grown Plantago lanceolata and P. major were calculatedfrom data presented elsewhere. Results showed that for grown Ricinus the short term relativeuptake rates, for each nutrient X did not change significantly over the steady-state periodof exponential growth. The average gave , the mean relative uptake rate during exponential growth, for each nutrient. The amountof each nutrient taken up from a nutrient solution over a periodof time could, therefore, be calculated. For and -grown R. communis,the relative uptake rate of each nutrient was a constant fractionof the relative rate of carbon assimilation. It is suggestedthat this is typical of plants of cauline habit. For both Plantago spp., the relative rates of nitrogen uptakeand assimilation fell significantly during the exponential growthphase It is suggested that this could be a characteristic ofthe growth habit of the rosette plant. Key words: Relative uptake rates, Ricinus, Plantago, ammonium, nitrate, cauline, rosette     

White Clover N2-Fixation in Response to Root Temperature and Nitrate: I GROWTH AND UPTAKE OF NITRATE FROM FLOWING NUTRIENT SOLUTIONS

Established, nodulated white clover plants (Trifolium repensL. cv. Blanca) were transferred to eight plant culture unitsof a system of flowing solution culture. Solution temperatureswere 5, 11, 17, and 25 ?C (two units per temperature), withshoot temperature of 25/15 ?C day/night and light regime commonto all plants. After 7 d, was supplied at 10 mmol m^–3 to one of each pair of culture units and thenet uptake of was monitored over 14 d. The remaining four culture units served as controls in which plantswere entirely dependent on N₂ fixation, as estimated by sequentialharvesting and the change in the amount of N in plants. Totalfresh and dry weights increased exponentially with time andwith increasing root temperature, between 5–25 ?C in nitrateplants and 5–17 ?C in control plants, respectively, byfactors of 2.9 and 1.8. Nodule dry weight of nitrate plantsshowed little increase after 6 d compared with control plants.Dry weight shoot: root ratios increased with time in all treatmentsexcept 5 ?C control plants. Total net uptake of over 13 d was 0.41, 4.27, 11.92, and 12.77 mmol plant-1, respectively,at 5, 11, 17, and 25 ?C. At all temperatures except 5 ?C, plantsaccumulated high concentrations of (10–40 mol m^–3) in leaflets and roots, within 2 or 3 days ofsupplying . Daily mean unit absorption rates of increased 12-fold with increasing temperature between 5 and 25 ?C, and showed little change with time at 5,17, and 25 ?C. The total N₂ fixed by nitrate plants over 14d increased 5-fold with temperature between 5 and 17 ?C, butwas always less than the amount fixed by control plants. Thepercentage contributed by N2 fixation to total N acquisitionby nitrate plants over 14 d decreased with increasing temperature,from 77% at 5 ?C to 11 % at 25 ?C. Mean daily rates of N₂ fixationper unit dry weight of nodule were lower in nitrate plants thanin control plants throughout treatment at 5 ?C and 25 ?C, butat 11 ?C and 17 ?C the rates for nitrate plants increased progressivelywith time and exceeded the rates for control plants after 8d. In both nitrate and control plants the effect of temperatureon N₂ fixation per nodule dry weight was proportionately lessthan that on unit absorption rate of . The results are discussed in terms of the overall regulation ofN accumulation by white clover and the adaptive significanceof differences in the sensitivities of uptake and N₂ fixation to root temperature. Key words: Trifolium repens, white clover, root temperature, N₂ fixation, nitrate uptake     

Nitrate Transport Characteristics in Hordeum vulgare L. Seedlings using Three Different Tracer Techniques

Deane-Drummond, C. E. and Thayer, J.R. 1986. Nitrate transportcharacteristics in Hordeum vulgare L. seedlings using threedifferent tracer techniques.—J. exp. Bot. 37: 429–439. and have been used to investigate various properties of nitrate uptake and translocation intoHordeum vulgare L seedlings. Short term / influx into seed lings grown in CaSO⁴ was stimulated by after a lag of 2 h. The apparent kinetics of shortterm / influx over the concentration range 0?0–0?7mol m fitted Michaelis-Menten equations The apparent V_max didnot change when seedlings were used that had been pretreatedin 10 or 100 mmol m^–3 and V^max=3.77 and 3?56µmol g^–1 fr. wt. h^–1respectively. The apparent Michaelis constants were also similarand K_m=0?47 and 0?45 mol m^–3 respectively. Longer term pulse chase experiments with the heavy isotope ¹⁵Nhave shown that feeding roots with resulted in the preferential appearance of ¹⁵N labelled aminoacids in the xylem sap. Pulse chase experiments with the radioisotope¹³N have shown that feeding shoots with resulted in a radial pattern of distnbution of labelin the leaf veins, which can be detected using autoradiography. The limitations and advantages of all three techniques are comparedby reference to other known experimental data. Key words: ³⁶Chlorate, ¹³nitrate, ¹⁵nitrate, Hordeum vulgare     

Compensatory Changes in Ion Fluxes into Barley (Hordeum vulgare L. cv. Betzes) Seedlings in Response to Differential Root/Shoot Growth Temperature

The effect of growth temperature on the short term influx of⁸⁶Rb⁺/K⁺, ³⁶Cl^–/Cl^–, , ⁴⁵Ca²⁺/Ca²⁺and into barley plants (Hordeum vulgareL. cv. Betzes) has been examined. When barley plants were grownwith a differential root: shoot temperature (15 ?C/25 ?C) therewas a marked stimulation of influx of all ions except Ca²⁺.Q₁₀ measurements were close to 2.0 for all ions except Ca²⁺,where Q₁₀ 1.0 was found. Kinetics of ion influx showed thatthere had been almost complete compensation for the lower growingtemperature over a range of concentrations. The regulation of uptake was affected by growth temperature. On exposure to 15?C efflux/influx fell initially but was restored after 5 d. Sensitivity of net uptake to was increased by growth at a lower temperature. The importance of these observations in relationto application to field experiments and the proposed mechanismfor uptake is discussed. Key words: Growth temperature, Nitrate, Ammonium     

Nitrate Nutrition of Grasses from Steady-State Supplies in Flowing Solution Culture following Nitrate Deprivation and/or Defoliation: II. ASSIMILATION OF AND SHORT-TERM EFFECTS ON UPTAKE

Plants of two genotypes of Lolium perenne L. cv. S23 and a L.perenne ? L. multiflorum Lam. hybrid cv. Augusta were grownin flowing solution culture. N was suppled in one treatmentat 10 mmol m^–3 NO^–3 throughout (HN), and in another(LN) the N supply was terminated after 10 d for 11 d. When was re-supplied both LN and HN plants were leftentire or defoliated. The two genotypes showed similar responsesto all treatments. The concentration of N in shoot dry matterdeclined from 4.4% to 2.0% and in the root from 2.8% to 1.0%over the 11 d of N deprivation, with 95% of the initially present being assimilated during this period. LN plantsassimilated 10% more of their total uptake than did HN plants. The in vitro nitrate reductase activity(NRA) was 10- to 50-fold higher in the youngest fully-expandedleaves than in roots and declined in the leaves during N deprivation.Between 2–6 d after defoliation, there was a large increasein NRA in leaves of HN (but not LN) plants. After defoliationof HN plants, net uptake from 10 mmol m^–3 declined to negligible levels within 15 h, but in defoliatedLN plants it increased to levels similar to those of entireHN plants (15–20 µmol h^–1 g^–1 fr. wt.root) within 8 h. When was re-supplied to entire LN plants, uptake of increased to levels similar to those of entire HN plants within 2.3 h, butdid not markedly exceed that of HN plants for at least 10 h.Net uptake of by LN plants during depletion of stirred static nutrient solutions containing 1.0 mol m^–3 lagged behind that by HN plants by 70–100 min, but the maximum unit absorption rate was similar for LNand HN plants (5–7 µmol h^–1 g^–1 fr.wt. root). The nature of the short-term demand for uptake following recovery from the stresses of defoliation andN starvation is discussed. Key words: Lolium perenne, Lolium multiflorum, N-deficiency, defoliation, nitrate uptake, nitrate reductase, N-assimilation     

Translocation of Some Anions, Cations, and Acids in Turnip (Brassica napus L.) Mitochondria

The translocation of various anions, cations, and acids acrossthe membrane system of turnip mitchondria has been investigatedby light scattering techniques. The results imply that the membranesof turnip mitochondria are not permeable to choline, K⁺, Na⁺,, , , and . It has been established that Cl^–,, and SCN– passively permeate the mitochondrial membrane. It is probable that permeates as NH₃ and that and cross the membrane either as the corresponding acid or on ananion/ hydroxide antiporter. The alkali metals Na⁺ and K⁺ equilibrateacross the membrane via specific H⁺/Na⁺ and H⁺/K⁺ antiporters,having similar activity at neutral pH.     

Intracellular pH Regulation in Ricinus communis Grown with Ammonium or Nitrate as N Source: The Role of Long Distance Transport

Allen, S. and Raven, J. A. 1987. Intracellular pH regulationin Ricinus communis grown with ammonium or nitrate as N source:the role of long distance transport.—J. exp. Bot. 38:580–596. Charge balance and intracellular pH regulation were studiedin Ricinus communis grown in water culture with 1–0 molm^–3 or l-0 mol m ^–3 as sole N source. Seedling and 70-d-old plant parts were analysed for total P, C, organic N and S, and ash alkalinity;xylem and phloem saps were analysed for mineral ion content,and amino acids, amides, and dicarboxylates. Excreted H⁺ andbase were also measured. It was shown that in -N plants, H ⁺ produced and excreted directly bythe roots accounted for all net —COOH produced in theplant, but not for cation uptake by net H⁺ exchange. IntracellularpH perturbation in the shoot was regulated partly by reduction and partly by the transportof OH^- -generating dicarboxylates in the xylem. Phloem sap hadthe capacity to transport organic N and carboxylates excessto shoot requirements back to the root. In -N plants, 60% of total reduction occurred in the root, and 70% of all OH^- produced by root and reduction was excreted directly as base. Very little —COO^–from root reduction was stored in the root: most was transported to the shoot as xylem dicarboxylateand stored in the shoot. Of the OH^- produced from shoot and reduction, 40% was stored as shoot carboxylate: the phloem saphad the capacity to transport the rest back to the roots whereit was excreted as base. Key words: Intracellular pH, ammonium nutrition, nitrate nutrition, xylem dicarboxylates, phloem dicarboxylates, charge balance     

The Role of Long-distance Transport in Intracellular pH Regulation in Phaseolus vulgaris Grown with Ammonium or Nitrate as Nitrogen Source, or Nodulated

Charge balance and intracellular pH regulation were studiedin Phaseolus vulgaris grown in water culture on or as N source, or nodulated and in N-free medium. Seedlings and 36-d-old plants were analysed for total P, C, organic N and S and ash alkalinity;xylem sap was analysed for mineral ion content and amino acids,amides and dicarboxylates. Both water uptake and H⁺ or baseexcreted during water culture were measured. It was shown that in -grown plants, H⁺ excretedwas related directly to the uptake and assimilation of ; there was no cation uptake associated with netH⁺ exchange. All shoot N was supplied as organic N, mainly glutamine,so that shoot pH perturbation would be limited to uronate productionin situ. This could be regulated by both shoot reduction and the transport of OH^–-generating carboxylatesin the xylem. In plants on , the great majority of reduction occurred in the root and most of the OH^–produced was converted to -COO^–, transported up the xylemand stored, so that the leaves in particular had a high ashalkalinity (20-fold that in the roots). Some OH^–, however,was excreted. Nodulated plants had a low N content, compared with the others,indicating a low rate of N₂-fixation for the earlier periodof water culture. At harvest, however, the xylem sap organicN content was comparable to that of plants. H⁺ excretion was in excess of that required for N assimilation.It was concluded that in these plants some net H⁺/cation exchangehad occurred which may have been a response to low nutrient(i.e. nitrogen) status. Key words: Phaseolus vulgaris, pH regulation, nitrate nutrition, ammonium nutrition, dinitrogen fixation, xylem sap composition.