A comparison of nitrate transport in four different rice(Oryza sativa L.) cultivars

As rice can use both nitrate (NO3-) and ammonium (NH4+), we have tested the hypothesis that the shift in the pattern of cultivars grown in Jiangsu Province reflects the ability of the plants to exploit NO3- as a nitrogen (N) source. Four rice cultivars were grown in solution culture for comparison of their growth on NO3- and NH4+ nitrogen sources. All four types of rice,Xian You 63 (XY63), Yang Dao 6 (YD), Nong Keng 57 (NK) and Si You 917 (SY917), grew well and produced similar amounts of shoot biomass with 1 mmol/L NH4+ as the only N source.However, the roots of NK were significantly smaller in comparison with the other cultivars. When supplied with 1 mmol/L NO3-, YD produced the greatest biomass; while NK achieved the lowest growth among the four cultivars. Electrophysiological measurements on root rhizodermal cells showed that the NO3--elicited changes in membrane potential (ΔEm) of these four rice cultivars were significantly different when exposed to low external NO3- (＜1 mmol/L); while they were very similar at high external NO3- (10 mmol/L). The root cell membrane potentials of YD and XY63 were more responsive to low external NO3- than those of NK and SY917. The ΔEm values for YD and XY63 rhizodermal cells were almost the same at both 0.1 mmol/L and 1 mmol/L NO3-;while for the NK and SY917 the values became larger as the external NO3- increased. For YD cultivar, ΔEm was measured over a range of NO3- concentrations and a Michaelis-Menten fit to the data gave a Km value of 0.17 mmol/L. Net NO3- uptake depletion kinetics were also compared and for some cultivars (YD and XY63) a single-phase uptake system with first order kinetics best fitted the data; while other cultivars (ND and SY917) showed a better fit to two uptake systems. These uptake systems had two affinity ranges: one had a similar Km in all the cultivars (0.2 mmol/L); the other much higher affinity system (0.03 mmol/L) was only present in NK and SY917. The expression pattern of twelve different NO3- transporter genes was tested using specific primers, but only OsNRT1.1 and OsNRT2. 1 expression could be detected showing significant differences between the four rice cultivars. The results from both the physiological and molecular experiments do provide some support for the hypothesis that the more popular rice cultivars grown in Jiangsu Province may be better at using NO3- as an N source.     

A comparison of nitrate transport in four different rice (Oryza sativa L.) cultivars

As rice can use both nitrate (NO ⁻₃ ) and ammonium (NH ⁺₄ ), we have tested the hypothesis that the shift in the pattern of cultivars grown in Jiangsu Province reflects the ability of the plants to exploit NO ⁻₃ as a nitrogen (N) source. Four rice cultivars were grown in solution culture for comparison of their growth on NO ⁻₃ and NH ⁺₄ nitrogen sources. All four types of rice, Xian You 63 (XY63), Yang Dao 6 (YD), Nong Keng 57 (NK) and Si You 917 (SY917), grew well and produced similar amounts of shoot biomass with 1 mmol/L NH ⁺₄ as the only N source. However, the roots of NK were significantly smaller in comparison with the other cultivars. When supplied with 1 mmol/L NO ⁻₃ , YD produced the greatest biomass; while NK achieved the lowest growth among the four cultivars. Electrophysiological measurements on root rhizodermal cells showed that the NO ⁻₃ -elicited changes in membrane potential (†E _m) of these four rice cultivars were significantly different when exposed to low external NO ⁻₃ (<1 mmol/L); while they were very similar at high external NO ⁻₃ (10 mmol/L). The root cell membrane potentials of YD and XY63 were more responsive to low external NO ⁻₃ than those of NK and SY917. The †E _m values for YD and XY63 rhizodermal cells were almost the same at both 0.1 mmol/L and 1 mmol/L NO ⁻₃ ; while for the NK and SY917 the values became larger as the external NO ⁻₃ increased. For YD cultivar, †E _m was measured over a range of NO ⁻₃ concentrations and a Michaelis-Menten fit to the data gave aK _m value of 0.17 mmol/L. Net N ⁻₃ uptake depletion kinetics were also compared and for some cultivars (YD and XY63) a single-phase uptake system with first order kinetics best fitted the data; while other cultivars (ND and SY917) showed a better fit to two uptake systems. These uptake systems had two affinity ranges: one had a similarK _m in all the cultivars (0.2 mmol/L); the other much higher affinity system (0.03 mmol/L) was only present in NK and SY917. The expression pattern of twelve different N ⁻₃ transporter genes was tested using specific primers, but onlyOsNRT1. 1 andOsNRT2.1 expression could be detected showing significant differences between the four rice cultivars. The results from both the physiological and molecular experiments do provide some support for the hypothesis that the more popular rice cultivars grown in Jiangsu Province may be better at using NO ⁻₃ as an N source.

     

The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

Nitrate Inhibition of Chloride Influx in Barley: Implications for a Proposed Chloride Homeostat

Net accumulation of Cl^– by intact barley plants was virtuallyeliminated in roots and reduced by 40% in shoots when externalmedia (0.5 mol m^–3 CaSO₄ plus 0–5 mol m^–3KCI) 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 3–6 h. Kinetic analyses revealed that the inhibitionof 36C1^– influx by external NO₃^- was complex. At 0.25mol m^–3 NO₃^- the V_max for Cl^– influx was reducedby greater than 50%, with insignificant effects upon K_m. At0.5 mol m^–3 NO₃^- there was no further effect upon V_maxbut K_m for influx increased from 38±5 mmol m^–3to 116±26 mmol m^–3. 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 Cl^–accumulation, 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     

Nodule Function in Symbiotic Bambara Groundnut (Vigna subterraneaL.) and Kersting's Bean (Macrotyloma geocarpumL.) is Tolerant of Nitrate in the Root Medium

Nitrogen-fixing activity in two nodulated African legumes, Bambaragroundnut (Vigna subterraneaL.) and Kersting's bean (MacrotylomageocarpumL.), was assessed in the presence of nitrate (NO₃^-)ions in the rooting medium. Nitrogenase activity was unimpairedby the supply of 5 mol m^-3NO₃to both species. Also, large concentrationsof ureides dominated the transpiration stream of NO₃-fed plants.Compared to other symbiotic legumes cultured with similar NO₃concentrations,nodule functioning in the tested landraces of Bambara groundnutand Kersting's bean is tolerant of NO₃ions in the rhizosphere.The potential benefits of such naturally occurring NO₃-tolerantsymbioses are substantial, as they would permit inorganic Nfertilizer application in intercropping systems without inhibitingN₂fixation in the associated legumes.Copyright 1998 Annals ofBotany Company NO₃tolerance, Bambara groundnut, Kersting's bean, nitrogenase activity, xylem ureides.     

Plant Growth in Relation to the Supply and Uptake of NO3-: A Comparison Between Relative Addition Rate and External Concentration as Driving Variables

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

Nitrate Transport into Chara corallina Cells using 36ClO-3 as an Analogue for Nitrate: I. INTERACTION BETWEEN 36ClO-3 AND NO-3 AND CHARACTERIZATION OF 36CIO-3/NO-3 INFLUX

The use of chlorate as an analogue for NO^–₃ during nitrateuptake into Chara corallina cells has been investigated. NO^–₃inhibits ³⁶C1O^–₃ influx into Chara over the concentrationrange 0–1000 mmol m^–3. Lineweaver-Burke plots ofthe data are characteristic of competitive inhibition by NO^–3in the low concentration range (0–300 mmol m^–3 ClO^–₃)and apparent K_INO3 is 140 mmol m^–3 which is of a similarorder of magnitude as apparent K_mCIO3- 180 mmol m^–3. Athigher substrate concentrations the inhibition by NO^–₃was not characteristic of competitive or uncompetitive inhibition. ³⁶C1O^–₃/NO^–₃ influx was dependent on K⁺ and Ca²⁺in the external medium and inhibited by FCCP. NO^–₃ pretreatmentor N starvation increased subsequent ³⁶C1O^–₃/NO^–₃influx into Chara. A comparison between rates of net NO^–₃uptake and ³⁶C1O^–₃/NO^–₃ influx supported the previoushypothesis that NO^–₃ efflux is an important componentin the determination of overall uptake rates. Key words: Nitrate, Chara, ³⁶CIO^–₃     

Nitrate Stimulation of Mobilization of Seed Reserves in Temperate Cereals: Importance of Water Uptake

Relationships between nitrate (NO^-₃) supply, uptake and assimilation,water uptake and the rate of mobilization of seed reserves wereexamined for the five main temperate cereals prior to emergencefrom the substrate. For all species, 21 d after sowing (DAS),residual seed dry weight (d.wt) decreased while shoot plus rootd.wt increased (15–30%) with increased applied NO^-₃concentrationfrom 0 to 5–20 mM . Nitrogen (N) uptake and assimilationwere as great with addition of 5 mM ammonium (NH⁺₄) or 5 mMNO^-₃but NH⁺₄did not affect the rate of mobilization of seedreserves. Chloride (Cl^-) was similar to NO^-₃in its effect onmobilization of seed reserves of barley (Hordeum vulgare L.).Increased rate of mobilization of seed reserves with additionalNO^-₃or Cl^-was associated with increases in shoot, root and residualseed anion content, total seedling water and residual seed watercontent (% water) 21 DAS. Addition of NH⁺₄did not affect totalseedling water or residual seed water content. For barley suppliedwith different concentrations of NO^-₃or mannitol, the rate ofmobilization of seed reserves was positively correlated (r >0.95)with total seedling water and residual seed water content. Therate of mobilization of seed reserves of barley was greaterfor high N content seed than for low N content seed. Seed watercontent was greater for high N seed than for low N seed, 2 DAS.Additional NO^-₃did not affect total seedling water or residualseed water content until 10–14 DAS. The effects of seedN and NO^-₃on mobilization of seed reserves were detected 10and 14 DAS, respectively. It is proposed that the increasedrate of mobilization of seed reserves of temperate cereals withadditional NO^-₃is due to increased water uptake by the seedlingwhile the seed N effect is due to increased water uptake bythe seed directly. Avena sativa L.; oat; Hordeum vulgare L.; barley; Secale cereale L.; rye; xTriticosecale Wittm.; triticale; Triticum aestivum L.; wheat; nitrate; seed; germination; seed reserve mobilization     

The Influence of Nitrate and Ammonium Nutrition on the Growth of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

The effects of NO^-₃ and NH⁺₄ nutrition on hydroponically grownwheat (Triticum aestivum L.) and maize (Zea mays L.) were assessedfrom measurements of growth, gas exchange and xylem sap nitrogencontents. Biomass accumulation and shoot moisture contents ofwheat and maize were lower with NH⁺₄ than with NO^-₃ nutrition.The shoot:root ratios of wheat plants were increased with NH⁺₄compared to NO^-₃ nutrition, while those of maize were unaffectedby the nitrogen source. Differences between NO^-₃ and NH⁺₄-fedplant biomasses were apparent soon after introduction of thenitrogen into the root medium of both wheat and maize, and thesedifferences were compounded during growth. Photosynthetic rates of 4 mM N-fed wheat were unaffected bythe form of nitrogen supplied whereas those of 12 mM NH⁺₄-fedwheat plants were reduced to 85% of those 12 mM NO^-₃-fed wheatplants. In maize supplied with 4 and 12 mM NH⁺₄ the photosyntheticrates were 87 and 82% respectively of those of NO^-₃-fed plants.Reduced photosynthetic rates of NH⁺₄ compared to NO^-₃-fed wheatand maize plants may thus partially explain reduced biomassaccumulation in plants supplied with NH⁺₄ compared to NO^-₃ nutrition.Differences in the partitioning of biomass between the shootsand roots of NO^-₃-and NH⁺₄-fed plants may also, however, arisefrom xylem translocation of carbon from the root to the shootin the form of amino compounds. The organic nitrogen contentof xylem sap was found to be considerably higher in NH⁺₄- thanin NO^-₃-fed plants. This may result in depletion of root carbohydrateresources through translocation of amino compounds to the shootin NH⁺₄-fed wheat plants. The concentration of carbon associatedwith organic nitrogen in the xylem sap of maize was considerablyhigher than that in wheat. This may indicate that the shootand root components of maize share a common carbon pool andthus differences induced by different forms of inorganic nitrogenare manifested as altered overall growth rather than changesin the shoot:root ratios.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize, nitrogen, growth, photosynthesis, amino acids, xylem     

The Influence of NO-3 and NH+4 Nutrition on the Gas Exchange Characteristics of the Roots of Wheat (Triticum aestivum) and Maize (Zea mays) Plants

Respiratory oxygen consumption by roots was 1·4- and1·6-fold larger in NH⁺₄-fed than in NO^-₃-fed wheat (Triticumaestivum L.) and maize (Zea mays L.) plants respectively. Higherroot oxygen consumption in NH⁺₄-fed plants than in NO^-₃-fedplants was associated with higher total nitrogen contents inNH⁺4-fed plants. Root oxygen consumption was, however, not correlatedwith growth rates or shoot:root ratios. Carbon dioxide releasewas 1·4- and 1·2-fold larger in NO⁺3-fed thanin NH⁺₄-fed wheat and maize plants respectively. Differencesin oxygen and carbon dioxide gas exchange rates resulted inthe gas exchange quotients of NH^-₄-fed plants (wheat, 0·5;maize, 0·6) being greatly reduced compared with thoseof NO^-₃-fed plants (wheat, 1·0; maize, 1·1). Measuredrates of HCO^-₃ assimilation by PEPc in roots were considerablylarger in 4 mM NH⁺₄-fed than in 4 NO^-₃ plants (wheat, 2·6-fold;maize, 8·3-fold). These differences were, however, insufficientto account for the observed differences in root carbon dioxideflux and it is probable that HCO^-₃ uptake is also importantin determining carbon dioxide fluxes. Thus reduced root extension in NH⁺₄-fed compared with NO^-₃-fedwheat plants could not be ascribed to differences in carbondioxide losses from roots.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize assimilation, ammonium assimilation, root respiration     

Effect of Ethylene and Culture Environment on Rice Callus Proliferation

Modifications to the gaseous envelope by callus during culturein Petri dishes were shown to reduce growth and promote necrosisof several rice (Oryza sativa L.) cultivars. Incubatingcallusunder a continuous flow of gas mixtures of known compositionsuggested that the inhibition of growth was caused by the accumulationof ethylene, the depletion of oxygen and, to a lesser extent,the accumulation of carbon dioxide. In order to evaluate theimportance of ethylene accumulation aminoethoxyvinylglycine(AVG), 1-aminocyclopropane-l-carboxylic acid (ACC and silvernitrate (AgNO₃), were added to the nutrient medium and ethylenemeasurements performed during callus culture. Ethylene restrictedcallus growth particularly under high (35 °C) as comparedto moderate (25 °C) temperatures and under illuminated ascompared to darkened incubation. Under illuminated incubationat 25 °C AVG (5 mmol m^–3) and AgNO°(50 mmol m^–3)significantly improvedcallus growth (100 and 60% respectively)while ACC (200 mmol m^–3) significantly decreased growth(40%). AVG and AgNO₃ were less effective under dark incubationat 25 °C where ethylene production was lower. Furthermore,callus growth was significantly better in large as comparedto small culture vessels since the ethylene concentration wasdiluted and more oxygen was available for respiration. Bettercontrol of ethylene and increased oxygen availability couldbe a way ofproducing healthy callus for the formation of embryogenictissues of otherwise recalcitrant cultivars of rice (e.g. IndicaIR42) and may be a way of improving manipulation of other cerealspecies. Key words: 1-Aminocyclopropane-1-carboxylic acid, aminoethoxyvinylglycine, callus, ethylene, Oryza sativa, silver nitrate     

Influence of Chloride and Transpiration on Net15NO3-Uptake Rate byCitrus Roots

Three-month-old Carrizo citrange (hybrid of Citrus sinensisL. OsbeckxPoncirus trifoliata Blanco) seedlings were grown incontrolled environment chambers in pots of fine sand. Plantswere irrigated with either non-saline or saline solutions overa 3-week period. After these treatments, plants were transferredto vessels containing a 5 m M¹⁵NO₃K (96% atom excess¹⁵N) solution,and transpiration as well as concentration of¹⁵N and Cl^-in roots,stem and leaves were measured after 24 h. Transpiration and¹⁵NO₃^-uptakerates were inhibited after exposure to NaCl and the concentrationof salt pre-treatment determined the intensity of this inhibitoryeffect. To determine the effect of transpiration on NO₃^-absorption,net¹⁵NO₃^-uptake rate was measured in salt stressed and non-stressedplants exposed to different light intensities or relative humiditiesand also in detached roots. Reduction in NO₃^-uptake was moreclosely related to Cl^-antagonism from salt stress than to reducedtranspiration rate. Copyright 1999 Annals of Botany Company Nitrate, absorption, inhibition transport system, salt, light and humidity.     

Acclimation of NO-3 fluxes to low root temperature by Brassica napus in relation to NO-3 supply

Acclimation of NO^–₃ transport fluxes (influx, efflux)in roots of oilseed rape (Brassica napus L. cv. Bien venu) andtheir sensitivity to growth at low root temperature was studiedin relation to external NO^–₃ supply, defined by constantconcentrations ranging from sub- to supra-optimal with respectto plant growth rate. Plants were grown from seed in flowingnutrient solutions containing 250 mmol m^–3 NO^–₃at 17°C for 20d, and solution temperature in half the cultureunits was then lowered decrementally over 3 d to 7°C. Threedays later plants were supplied with NO^–₃ at 1, 10, 100or 1000 mmol m^–3 maintained for 18 d. Dry matter productionwas decreased more by low root zone temperature than low [NO^–₃]_e. Root specific growth rates were inversely related to [NO^–₃]_eand shoot:root ratios increased with time at [NO^–₃]_e between10–1000 mmol m^–3. Net uptake of NO^–₃ at 17°Cwas twice that at 7°C, and at both temperatures it doubledwith increasing [NO^–₃]_e between 1–10 mmol m^–3with further small increases at higher [NO^–₃]_e. Mean unitabsorption rates of NO^–₃ between 0–6 d and 6–14d were linearly related (r² of 0.79–0.99) to log₁₀[NO].Steady-state Q₁₀ (7–17°C) for uptake between 0–6d were 0.91, 1.62, 1.27, and 1.10, respectively, at [NO^–₃]_eof 1, 10, 100, and 1000 mmol m^–3, compared with correspondingvalues of 0.98, 1.38, 1.68, and 1.89 between 6–14 d. Thedata indicated that net uptake rates at 7 and 17°C divergedover time at high [NO^–₃]_e. Short-term uptake rates from1 mol m^–3 NO^–₃ measured at 17°C were higherin plants grown with roots at 7°C than at 17°C; for7°C plants there was a strong inverse linear relationship(r²=0.94) between uptake rate and treatment log₁₀ [NO^–₃]_ewhilst rates in 17°C plants were independent of prior [NO^–₃]_e. Rates of NO^–₃ influx and efflux under different steady-stateconditions of NO^–₃ supply and root temperature were calculatedfrom dilution of ¹⁵N added to culture solutions. Efflux wassubstantial relative to net uptake in all treatments, and wasinversely related to [NO^–₃]_e at 17°C but not at 7°C.Ratios of influx: efflux ranged from 1.6–2.9 at 17°Cand 1.3–1.8 at 7°C, indicating the proportionatelygreater impact of efflux at low root temperature. Ratios ofefflux: net uptake were 0.53–1.56 at 17°C and 1.21–3.58at 7°C. The apparent sensitivities of influx and effluxto steady-state root temperature varied with [NO^–₃]_e.Both fluxes were higher at 17°C than 7°C in the presenceof 100–1000 mmol m^–3 NO^–₃ but the trend wasreversed at 1–10 mmol m^–3 NO. Concentrations oftotal N measured in xylem exudate were at least 2-fold higherat 7°C compared with 17°C, attributable mainly to higherconcentrations of NO^–₃ glutamine and proline. The resultsare discussed in terms of acclimatory and other responses shownby the NO^–₃ transport system under conditions of limitingNO^–₃ supply and low root temperature. Key words: Brassica napus, nitrate supply, efflux, influx, root temperature, xylem exudate     

Nutrient Uptake and Organic Acid Anion Metabolism in Lupins and Peas Supplied with Nitrate

Unlike many plants reported in the literature, lupins do notexcrete OH^- in amounts equivalent to the net excess of inorganicanion uptake over inorganic cation uptake. To investigate themechanisms involved in the maintenance of charge balance, nutrientuptake and organic anion accumulation of lupins and peas suppliedwith a range of NO^-₃ concentrations, were compared. Lupins absorbed less NO^-₃ than peas on a dry weight basis, whichlargely accounted for the smaller excess of anion uptake overcation uptake in lupins than in peas at the same NO^-₃ supply.When anion uptake exceeded cation uptake, peas excreted an equivalentcharge of OH^-, whereas lupins excreted much smaller amountsof OH^- than the excess of anion over cation uptake. It was calculatedthat lupins excreted significant amounts of organic anions whenanion uptake exceeded cation uptake, whereas organic anion excretionfrom peas was negligible, regardless of their NO^-₃ supply andcation-anion balance. In this study, organic anion excretion was measured from lupinroots grown in near-sterile conditions while supplied with NO^-₃at 0, 500 and 2000 µM. Although complete sterility wasnot achieved, there was close agreement between the organicanion excreted and the excess anion over cation uptake.Copyright1994, 1999 Academic Press Lupinus angustifolius L., Pisum sativum L., organic acid, nutrient uptake     

Nitrate Effects on Growth of the First Four Main Stem Leaves of a Range of Temperate Cereals and Pasture Grasses

The effects of different applied NO₃^– concentrations onextension growth and final length and area of leaves 1–4of five cereals and six pasture grasses of temperate originwere examined. Increased applied NO₃^– in the range 0.1–0.5.0mol m^–3 caused decreased duration of growth but increasedgrowth rate and final length of leaves 2–4 of the cerealsAvena saliva, Hordeum vulgare, Secale cereale, x Triticosecaleand Triticum aestivum. For all cereals, increased NO₃^–resulted in increased area of leaves 1–4. Pasture grasseswere supplied either 0.5 or 50 mol m^–3 NO₃^–. Increasedapplied NO₃^– (0.5–5.0 mol m^–3) resulted indecreased duration of growth and increased growth rate and finalarea of leaves 1–4 of Bromus wiltdenowii, leaves 2–4ofFestuca arundinaceae and leaves 3 and 4 of Lolium muitiflorum.In addition, length of leaves 3 and 4 of B. witidenowii increasedwith increased NO₃^–. Increased NO₃^– resulted inincreased area of leaves 2–4 of Dactylis gtomerata andLolium perenne and leaves 3 and 4 of Phalaris aquaiica but hadno effect on extension growth of all three species. Avena sativa L, oat, Hordeum vulgare L, barley, Secale cereale L, rye, x Triticosecale Wittm, triticale, Triticum aestivum L, wheat, Bromus willdenowii Kunth, prairie grass, Dactylis gtomerata L, cocksfoot, Festuca arundinaceae Shreb, tall fescue, Lolium multijlorum Lam, Italian ryegrass, Lolium perenne L, perennial ryegrass, Phalaris aquatica L, nitrate, leaf extension, leaf expansion     

Modulation of Sucrose Content by Fructose 2,6-bisphosphate during Photosynthesis in Rice Leaves Growing at Different Light Intensities

Reddy, A. R. and Das, V. S. R. 1987. Modulation of sucrose contentby fructose 2,6-bisphosphate during photosynthesis in rice leavesgrowing at different light intensities.—J. exp. Bot. 38:828–833. The relationship between the rate of CO₂ fixation and sucroseconcentration in the leaves of rice (Oryza sativa L.) grownat different light intensities was investigated. Maximum sucrosecontent coincided with maximum rates of CO₂ fixation, achievedat a photon flux density of 1600 µmol m^–2 s^–1.The levels of sucrose and fructose 2,6-bisphosphate were alsocompared in the leaves under different light intensities. Fructose2,6-Msphosphate accumulated during growth at low light. Theactivity of fructose-6-phosphate 2-kinase was high in the leavesgrown at low light while that of fructose-2,6-bisphosphatasewas low. The activities of phosphoglucose isomerase and phospho-glucomutasewere slightly increased by growth at low light The activitiesof UDP glucose pyrophosphorylase were adversely affected invitro with increased concentrations of fructose 2,6-bisphosphatewhile those of sucrose phosphate synthase were moderately affected.Phosphoglucose isomerase and phosphoglucomutase were activatedby fructose 2,6-bisphosphate (8-0 mmol m^–3) by 12-15%.The results suggested that low light intensities during growthresult in an accumulation of fructose 2,6-bisphosphate whichmodulates the key enzymes of sucrose biosynthesis thus regulatingcarbon flow under conditions of limited photosynthesis. Key words: Oryza sativa, photosynthesis, sucrose synthesis, fructose 2,6-bisphosphate, light     

Assimilation of 15N2 and 15NO3- by Partially Nitrate-Tolerant Nodulation Mutants of Soybean

Growth-chamber studies were conducted to evaluate nitrogen assimilationby three hypernodulated soybean [Glycine max (L.) Merr.] mutants(NOD1–3, NOD2–4, NOD3–7) and the Williamsparent. Seeds were inoculated at planting and transplanted atday 7 to nutrient solution with 1 mol m^–3 urea (optimizesnodule formation) or 5 mol m^–3 NO₃^– (inhibits noduleformation). At 25 d after planting, separate plants were exposedto ¹⁵NO₂ or ¹⁵NO₃^– for 3 to 48 h to evaluate N₂ fixationand NO₃^– assimilation. Plant growth was less for hypernodulatedmutants than for Williams with both NO₃^– and urea nutrition.The major portion of symbiotically fixed ¹⁵N was rapidly assimilated(30 min) into an ethanol-soluble fraction, but by 24 h aftertreatment the ethanolinsoluble fraction in each plant part wasmost strongly labelled. Distribution patterns of ¹⁵N among organswere very similar among lines for both N growth treatments aftera 24 h ¹⁵N₂ fixation period; approximate distributions were40% in nodules, 12% in roots, 14% in stems, and 34% in leaves.With urea-grown plants the totalmg ¹⁵N fixed plant^–1 24h^–1 was 1·18 (Williams), 1·40 (N0D1-3),107 (NOD2-4), and 0·80 (NOD3-7). The 5 mol m^-3 NO₃^- treatmentresulted in a 95 to 97% decrease in nodule mass and ¹⁵N₂ fixationby Williams, while the three mutants retained 30 to 40% of thenodule mass and 17 to 19% of the ¹⁵N₂ fixation of respectiveurea-grown controls. The hypernodulated mutants, which had restrictedroot growth, absorbed less ¹⁵NO₃^- than Williams, irrespectiveof prior N growthcondition. The ¹⁵N from ¹⁵NO₃^- was primarilyretained in the soluble fraction of all plant parts through24 h. The ¹⁵N incorporation studies confirmed that nodule developmentis less sensitive to external NO₃^- in mutant lines than in theWilliams parent, and provide evidence that subsequent metabolismand distribution within the plant was not different among lines.These results further confirm that the hypernodulated mutantsof Williams are similar in many respects to the hyper- or supernodulatedmutants in the Bragg background, and suggest that a common mutationalevent affectingautoregulatory control of nodulation has beentargeted. Key words: Glycine max (L.) Merr., soybean, N₂fixation, nitrate assimilation, nodulation mutants, ¹⁵N isotope     

The Specificity of the Carrier-Mediated Uptake of ABA by Root Segments of Phaseolus coccineus L.

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

Nitrate Effects on Growth of the First Four Main Stem Leaves of a Range of Temperate Cereals and Pasture Grasses

The effects of different applied NO₃^– concentrations onextension growth and final length and area of leaves 1–4of five cereals and six pasture grasses of temperate originwere examined. Increased applied NO₃^– in the range 0.1–50mol m^–3; caused decreased duration of growth but increasedgrowth rate and final length of leaves 2–4 of the cerealsAvena saliva, Hordeum vulgare, Secale cereale x Triticosecaleand Triticum aestivum. For all cereals, increased NO₃^–resulted in increased area of leaves 1-4. Pasture grasses weresupplied either 0.5 or 50 mol m^–3; NO₃^–. Increasedapplied NO₃^– (0.5–50 mol m^–3) resulted indecreased duration of growth and increased growth rate and finalarea of leaves 1–4 of Bromus willdenowii leaves 2–4of Festuca arundinaceae and leaves 3 and 4 of Lolium multiflorum.In addition, length of leaves 3 and 4 of B. willdenowii increasedwith increased NO₃. Increased NO₃ resulted in increased areaof leaves 2–4 of Daciylis glomerata and Lolium perenneand leaves 3 and 4 of Phalaris aquatica but had no effect onextension growth of all three species. Avena saliva L., oat, Hordeum vulgare L., barley, Secale cereaie L., rye, x Triticosecale Wittm, triticale, Triticum aestivum L., wheat, Bromus willdenowii Kunth, prairie grass, Dactylis glomerata L., cocksfoot, Festuca arundinaceae Shreb, tall fescue, Lolium multiflorum Lam, Italian ryegrass, Lolium perenne L, perennial ryegrass, Phalaris aquatica L, nitrate,, leaf extension, leaf expansion     

Effects of Chilling, Light and Nitrogen-containing Compounds on Germination, Rate of Germination and Seed Imbibition of Clematis vitalba L.

Effects of chilling (5 °C) period, light and applied nitrogen(N) on germination (%), rate of germination (d to 50% of totalgermination; T_50%) and seed imbibition were examined inClematisvitalba L. In the absence of chilling, light and N, germinationwas minimal (3%). When applied alone, both chilling and N increasedgermination. Chilling for 12 weeks increased germination to64%, and 2.5 mM NO^-₃or NH⁺₄increased germination to 10–12%.Light did not increase germination when applied alone, but didwhen applied in combination with chilling and/or N. Half theseed germinated when light was combined with 2.5 mM NO^-₃or NH⁺₄.The influence of chilling, light and/or N on germination wasgreater when combined, than when either factor was applied alone.Both oxidized (NO^-₃) and reduced (NH⁺₄) forms of N increasedgermination, but non-N-containing compounds did not, suggestingthe response was due to N and not ionic or osmotic effects. Without additional N, T_50%decreased from 16–20 d at zerochilling, to around 5 d at 8 and 12 weeks chilling. AlthoughT_50%was not influenced by an increase in NO^-₃or NH⁺₄from 0.5to 5.0 mM , it did increase with additional applied N thereafter.However, the magnitude of the N effect was small compared tothat of chilling. Like germination, seed imbibition increasedwith a longer chilling period, but in contrast imbibition decreasedslightly with increased applied NO^-₃or NH⁺₄. It is argued thatincreased imbibition is not directly related to an increasein total germination, but that it may be related to the rateof germination. Possible mechanisms involved in the reductionin dormancy ofC. vitalba seed are discussed. Clematis vitalba L.; germination; dormancy; imbibition; rate of germination; chilling; light; nitrate; ammonium; nitrogen; phytochrome