Nitrate Uptake and Assimilation by Wheat Seedlings during Initial Exposure to Nitrate

Nitrate uptake, reduction, and translocation were examined in intact, 14-day-old, nitrogen-depleted wheat (Triticum vulgare var. Knox) seedlings during a 9-hour exposure to 0.2 mm Ca (NO(3))(2). The nitrate uptake rate was low during the initial 3-hour period, increased during the 3- to 6-hour period, and then declined. By the 3rd hour, 14% of the absorbed nitrate had been reduced, and this increased to 36% by the 9th hour. Shoots accumulated reduced (15)N more rapidly than roots and the ratio of reduced (15)N to (15)N-nitrate was higher in the shoots. A significant proportion of the total reduction occurred in the root system under these experimental conditions. Accumulation of (15)N in ethanol-insoluble forms was evident in both roots and shoots by the 3rd hour and, after 4.5 hours, increased more rapidly in shoots than in roots.An experiment in which a 3-hour exposure to 0.2 mm Ca ((15)NO(3))(2) was followed by a 12-hour exposure to 0.2 mm Ca ((14)NO(3))(2) revealed a half-time of depletion of root nitrate of about 2.5 hours. A large proportion of this depletion, however, was due to loss of (15)N-nitrate to the ambient (14)N-nitrate solution. The remaining pool of (15)N-nitrate was only slowly available for reduction. Total (15)N translocation to the shoot was relatively efficient during the first 3 hours after transfer to Ca ((14)NO(3))(2) but it essentially ceased after that time in spite of significant pools of (15)N-nitrate and alpha-amino-(15)N remaining in the root tissue.     

Nitrite Uptake Patterns in Wheat Seedlings as Influenced by Nitrate and Ammonium

Nitrite and nitrate uptake by wheat (Triticum vulgare) from 0.5 mM potassium solutions both showed an apparent induction pattern characterized by a slow initial rate followed by an accelerated rate. The accelerated phase was more rapid for nitrate uptake, was initiated earlier, and was seriously restricted by the presence of equimolar nitrite. The accelerated phase of nitrite uptake was restricted by nitrate to a lesser extent. The two anions seem not to be absorbed by identical mechanisms. Ammonium pretreatments or prior growth with ammonium had relatively little influence on the pattern of nitrite uptake. However, prior growth with nitrate eliminated the slow initial phase and induced development of the accelerated phase of nitrite uptake. A beneficial effect was noted after 3 h nitrate pretreatment and full development had occurred by 12 h nitrate pretreatment. The evidence suggests that a small amount of tissue nitrite, which could be supplied either by absorption or by nitrate reduction, was specifically required for induction of the accelerated phase of nitrite uptake. Cycloheximide (2 μg ml^?1) seriously restricted development of the accelerated phase of nitrite uptake, but its effect was not as severe when it was added after the accelerated phase had been induced by prior exposure to nitrite or nitrate. However, translocation of ¹⁵N from the absorbed nitrite was sharply decreased under the latter conditions, indicating a difference in sensitivity of the uptake and translocation processes to cycloheximide. Potassium uptake was greater from KNO₃ than from KNO₂ and in both instances it was enhanced during the early stages of the accelerated phase of anion uptake. Moreover, addition of NaNO₃ to KNO₂ substantially increased potassium uptake. A coupling between anion and potassium uptake was therefore evident, but the coupling was not obligatory because the accelerated phase of nitrite uptake could occur in absence of rapid potassium uptake.     

Nitrate Uptake and the Induction of Nitrate Reductase Activity in Wheat (Triticum aestivum L.) Seedlings

Nitrate uptake and the subsequent induction of in vivo nitratereductase activity in wheat were studied by investigating aeuploid and certain ditelosomic stocks which exhibited in vivoactivity significantly greater than that of the euploid. Thekinetics of nitrate uptake were investigated, but the high activitiesof the ditelosomics were not caused by increased uptake of nitrate,although ditelo-7B^L exhibited unusual uptake dynamics. Analysisof the induction of nitrate reductase activity revealed a biphasicgeneral pattern, with an initial rapid phase being followedby a slower but longer period of induction. The induction rateover the second period, although responsible for only a minorproportion of the total activity induced, was positively correlatedwith the final nitrate reductase level, unlike the rate overthe first induction period. Several stocks exhibited high inductionrates over one or other of the two phases, while ditelo- 1 A^sshowed an abnormal monophasic induction pattern. At the endof the second period of induction, nitrate reductase activitybecame more or less steady, except for activity fluctuationsassociated with the time of application of induction stimuli.     

Root Morphology and Nitrogen Uptake of Maize Simultaneously Supplied with Ammonium and Nitrate in a Split-root System

We studied the response of maize (Zea mays L. cv. Anjou 256)to a simultaneous, but separated supply of ammonium and nitrate(localized supply, LS). A split-root system was used to supplyhalf of the roots with ammonium and the other half with nitrate.A homogeneously distributed supply of both nitrogen forms (HS)was the control treatment. Seedlings were grown for 12 d fromthe two-leaf to the three-leaf stage in hydroponics at threepH levels (4, 5·5 and 7). The total N concentration was3 mol m^-3. The split-root system was established by removingthe seminal root system and using only four nodal roots perplant. Total root length and root surface area were recordedautomatically with a modified Delta- T area meter. Other morphologicalroot traits (such as main axis length and diameter, number,density, and length of laterals) were recorded manually. Uptakeof ammonium and nitrate was measured by the depletion of thenutrient solution. As compared with LS, HS was superior in shootand root DM, total root length and root surface area, ammoniumand nitrate uptake and shoot nitrogen concentration, irrespectiveof pH level. This indicates that, also under field conditions,mixed ammonium and nitrate fertilization is only beneficialto plant growth if both N forms are evenly distributed in thesoil. At both HS and LS, ascending pH increased the ammonium:nitrateuptake ratio. At LS, declining pH induced a considerable shiftin the distribution of root DM, root length, and root surfacearea the nitrate-fed compartment.Copyright 1993, 1999 AcademicPress Maize, Zea may L., ammonium, nitrate, pH, root morphology, split-root     

Influence of Nitrogen Supply on Uptake and Translocation of Strontium and Calcium in Wheat Seedlings

Supplying nitrate to N-depleted wheat seedlings (Triticum vulgare cv. Knox) stimulated the uptake and translocation of both ⁸³Sr and ⁴⁵Ca. Since the increase in ⁴⁵Ca accumulation was greater, the ⁸⁵Sr/⁴⁵Ca ratio in the plant tissue was decreased. Nitrate had relatively little influence on the amount of the divalent cations and ⁸⁵Sr/⁴⁵Ca ratio in the exchangeable fraction on the root surfaces, whereas it greatly increased the uptake into root tissue and translocation to shoots. The increase in percent transported to shoots occurred largely in the period of most rapid nitrate uptake. A split root study indicated that nitrate was ineffective when it was supplied to a different portion of the root system than that exposed to ⁸⁵Sr and ⁴⁵Ca. Nevertheless, ammonium and urea also increased the translocation of the two cations, indicating that the effects of nitrate could not entirely be ascribed to a direct effect of the nitrate anion.     

稀土元囊对小麦幼苗氮素吸收及同化的影响

稀土元素浸种能够促进小麦(Triticum aestivum L.)幼苗对No3-的吸收,提高硝酸还原酶活力。这些效应与稀土浓度有关,低浓度有促进作用,高浓度则有抑制作用。稀土元素处理还能促进小麦幼苗体内No3-的同化还原,使硝态氮含量降低,氨基氮含量增加,促进了氮素代谢过程。     

Nitrogen Uptake by Apple Seedlings as Affected by Light, and Nutrient Stress in Part of the Root System

The adaptation of apple seedlings, Pyrus malus L., to localized nutrient stress was studied by measuring nitrogen uptake. Seedlings with split root systems were grown in nutrient solution. Various proportions of the roots were subjected to nutrient stress by placing some of the roots in water. The nitrogen uptake by stressed plants was measured under constant and varied lighting. Under optimum lighting it was found that if part of the root system was deprived of nitrogen, then the remainder partially compensated for this deficiency by increasing its uptake. This adaptation, however, was substantially reduced under low levels of lighting.     

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     

Improving Nitrogen Use Efficiency in Rice through Enhancing Root Nitrate Uptake Mediated by a Nitrate Transporter,NRT1.1B

<正>Nitrogen(N)is one of most important nutrients for crop production,which makes up 1%-5%of total plant dry matter(Marschner,2012).Due to the limited availability of N in soil,application of N fertilizers has been an important agronomic practice to increase crop yield.However,over-application of N fertilizers has caused pollution of N in soil,water and air.It     

Accelerated Nitrate Uptake in Wheat Seedlings: Effects of Ammonium and Nitrite Pretreatments and of 6-Methylpurine and Puromycin

The experiments reported herein had two objectives. One was to determine if the slow rate of nitrate uptake which occurs upon initial exposure of nitrogen-depleted wheat (Triticum vulgare cv. Knox) plants to nitrate was the result of insufficient reduced nitrogen. The second was to determine the impact of restrictions in ribonucleic acid or protein synthesis on both nitrate uptake and nitrate reduction. Pretreatments of 14-day-old seedlings for a few hours in ammonium or nitrite did not result in an enhancement of the initial slow rate of nitrate uptake. Growth for two additional weeks in ammonium also failed to eliminate the induction period. The evidence indicates that the presence of nitrate, rather than a product of its reduction, was required to initiate development of the accelerated rate of nitrate uptake. Puromycin (400 μg ml^?1) and 6-methylpurine (0.5 mM) prevented development of the accelerated phase of nitrate uptake. With both compounds, the relative restriction of nitrate uptake was greater than that of nitrate reduction as revealed by incorporation of ¹⁵N from labeled nitrate into reduced forms. The proportion of reduction which occurred in the root system under the imposed treatments could not be delineated precisely, preventing an unequivocal determination of the extent to which the two processes are coupled in the root system. The data nevertheless indicate nitrate reduction was closely associated with nitrate uptake. Accumulation of nitrate in the shoots was markedly restricted in presence of 6 methylpurine. This effect most likely was a result of a severe restriction in the translocation of nitrate into the xylem, rather than an increase in the reduction rate in the shoots.     

The Influence of Arginine-specific Reagents on Nitrate Uptake by Corn Seedlings

The effects of three arginine-specific reagents on uptake were studied using corn seedlings (Zea mays L., GoldenCross Bantam). In the presence of borate, 0.25 mM 2, 3-butanedione(BD) and 1.0 mM 1, 2-cyclohexanedione (CHD) inhibited uptake by 76% and 68%, respectively, compared tothe controls. However, in the absence of borate, only 18% and38% inhibition was observed for 0.25 mM BD and 1.0 mM CHD, respectively.Similarly, 0.5 mM phenylglyoxal (PGO) resulted in 75% inhibition.The degree of inhibition of nitrate uptake exhibited a concentration-dependencewith respect to the reagents. Corn seedlings are 2- or 3-foldmore sensitive to BD than to PGO and CHD, respectively, presumablydue to the unfavourable steric effects of the benzal ring. Uptakeof was partially restored after removal of BD, CHD, and PGO from the uptake medium. No significant differenceswere observed for the ATPase and plasma membrane-associatedvanadate-sensitive H⁺-ATPase or K⁺-stimulated ATPase activityin homogenates and microsomal fractions prepared from corn seedlingswhich had been incubated for 2 h in the presence or absenceof 0.5 mM BD or 1.0 mM PGO. This suggests that inhibition ofnitrate uptake by the arginine-specific reagents was not causedby the indirect effect of their binding and inhibiting H⁺-ATPase.The fact that the arginine-specific reagents strongly inhibit uptake indicates that the transport system has arginine residues at or near the activesite. Key words: Arginine-specific reagents, borate effect, nitrate uptake, reversibility     

Nitrogen and Nitrate Accumulation in Species Having Different Relationships Between Nitrate Uptake and Reduction

Species differ in the relationship of nitrate reductase activityto nitrate uptake. In Capsicum annuum different diurnal patternsof leaf nitrate reductase activity and nitrate uptake have beenreported. As a consequence, the relationship of free nitratein the plant to nitrate supplied has a higher level of significancethan has reduced nitrogen to nitrate supplied. In Zea mays ithas been reported that leaf nitrate reductase activity respondsdirectly to nitrate translocation to the leaf and in this speciesthe relationship of greatest significance is reduced nitrogencontent to nitrate supplied. In both species, and also in Cucumis melo, the proportion oftotal plant free nitrate and reduced nitrogen in the roots decreases,and in the stem increases, with increasing nitrate supplied. The accumulation of free nitrate in leaves is accompanied bya quantitatively different relationship between reduced nitrogenand dry weight compared to leaves not accumulating nitrate. Capsicum annuum. L., Cucumis melo L., melon, Zea mays L., maize, sweet corn, nitrate reductase, nitrate uptake     

氮沉降及菌根真菌对长白落叶松苗木根系构型及根际酶活性的影响

为探究氮沉降和接种菌根真菌对长白落叶松苗木根系构型和根际土壤酶活性的影响,以1年生长白落叶松(Larix olgensis)的盆栽菌根苗(简称+M,混合接种8种外生菌根真菌)和非菌根苗(简称-M,未接种处理)为研究对象,设置4个氮沉降处理(不施氮(0N,0 kg·N·hm^-1·yr^-1)、低氮(LN,15 kg·N·hm^-1·yr^-1)、中氮(MN,30 kg·N·hm^-1·a^-1)和高氮(HN,60 kg·N·hm^-1·a^-1)),测定直径0~0.5 mm根系的总根长、总表面积、总体积和根尖数等根系形态指标,对比分析氮沉降和接种菌根真菌处理对苗木根际土壤酶(β-1,4葡萄糖苷酶(BG)、亮氨酸氨基肽酶(LAP)、β-1,4-N-乙酰-氨基葡糖氨糖苷酶(NAG)、酸性磷酸酶(ACP)和碱性磷酸酶(ALP))活性的影响。结果表明:①长白落叶松苗木直径0~0.5 mm根系的总根长、总表面积、总体积和根尖数均随氮浓度的递增呈下降的趋势;在0N、LN和MN处理下,-M处理的根系形态指标均高于+M处理。②随氮浓度增加,+M和-M处理苗木根际土壤中BG、LAP、ACP和ALP活性均呈先增加后下降的趋势,而NAG活性呈下降的趋势。③+M和-M处理下,长白落叶松直径0~0.5 mm根系的形态指标与根际土壤BG活性均呈显著负相关关系(P<0.05);除根尖数外,其它根系形态指标与NAG活性相关性均为正相关(P<0.05)。综上所述,苗木菌根化处理削弱了氮沉降对落叶松苗木根系构型的影响;而低氮处理下,+M处理对苗木根际土壤酶的活化程度高于-M处理。     

Biomechanical Response of the Root System in Tomato Seedlings under Wind Disturbance

Wind disturbance as a green method can effectively prevent the overgrowth of tomato seedlings, and its mechanism may be related to root system mechanics. This study characterized the biophysical mechanical properties of taproot and lateral roots of tomato seedlings at five seedling ages and seedling substrates with three different moisture content. The corresponding root system-substrate finite element (FE) model was then developed and validated. The study showed that seedling age significantly affected the biomechanical properties of the taproot and lateral roots of the seedlings and that moisture content significantly affected the biomechanical properties of the seedling substrate (p < 0.05). The established FE model was sensitive to wind speed, substrate moisture content, strong seedling index, and seedling age and was robust. The multiple linear regression equations obtained could predict the maximum stress and strain of the root system of tomato seedlings in the wind field. The strong seedling index had the greatest impact on the biomechanical response of the seedling root system during wind disturbance, followed by wind speed. In contrast, seedling age had no significant effect on the biomechanical response of the root system during wind disturbance. In the simulation, no mechanical damage was observed on the tissue of the seedling root system, but there were some strain behaviors. Based on the plant stress resistance, wind disturbance may affect the growth and development of the root system in the later growth stage. In this study, finite element and statistical analysis methods were combined to provide an effective approach for in-depth analysis of the biomechanical mechanisms of wind disturbances that inhibit tomato seedlings’ growth from the root system’s perspective.     

Mineral Elements of Subtropical Tree Seedlings in Response to Elevated Carbon Dioxide and Nitrogen Addition

Mineral elements in plants have been strongly affected by increased atmospheric carbon dioxide (CO₂) concentrations and nitrogen (N) deposition due to human activities. However, such understanding is largely limited to N and phosphorus in grassland. Using open-top chambers, we examined the concentrations of potassium (K), calcium (Ca), magnesium (Mg), aluminum (Al), copper (Cu) and manganese (Mn) in the leaves and roots of the seedlings of five subtropical tree species in response to elevated CO₂ (ca. 700 μmol CO₂ mol^-1) and N addition (100 kg N ha^-1 yr^-1) from 2005 to 2009. These mineral elements in the roots responded more strongly to elevated CO₂ and N addition than those in the leaves. Elevated CO₂ did not consistently decrease the concentrations of plant mineral elements, with increases in K, Al, Cu and Mn in some tree species. N addition decreased K and had no influence on Cu in the five tree species. Given the shifts in plant mineral elements, Schima superba and Castanopsis hystrix were less responsive to elevated CO₂ and N addition alone, respectively. Our results indicate that plant stoichiometry would be altered by increasing CO₂ and N deposition, and K would likely become a limiting nutrient under increasing N deposition in subtropics.     

施氮对不同品种冬小麦植株硝态氮和硝酸还原酶活性的影响

以黄土高原南部半湿润区土垫旱耕人为土为供试土壤进行盆栽试验,以NR 9405、9430、偃师9号、小偃6号、陕229号和西农2208冬小麦品种为供试材料,研究施氮对不同品种冬小麦植株硝态氮含量和硝酸还原酶活性(NRA)的影响.结果表明,施氮能明显增加叶片NRA.不施氮时除小偃6号和偃师9号外,其余品种NRA在全生育时期的动态变化均呈双峰曲线,2个高峰期分别在返青期和开花期,且开花期高峰值(36.17 NO2-μg.-g 1FW.h-1)明显比返青期峰值(15.407 NO2-μg.-g 1FW.h-1)大;施氮时不同品种叶片NRA在全生育期呈单峰曲线变化,最高峰在开花期,平均峰值为80.93 NO2-μg.-g 1FW.h-1),比同期不施氮处理增加1倍以上.施氮后地上部硝态氮含量在各时期均显著提高,在小麦生育前期(出苗到拔节)表现最为显著.氮肥对不同品种硝态氮含量的影响程度基本上与对NRA的影响程度相反,即施氮后硝态氮增加幅度小的品种,NRA却增加幅度大.     

N2 Fixation and Nitrate Uptake by White Clover Swards in Response to Root Temperature in Flowing Solution Culture

Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown as simulated swards for 71 d in flowing nutrientsolutions with roots at 11 C and shoots at 20/15 C, day/night,under natural illumination. Root temperatures were then changedto 3, 5, 7, 11, 13, 17 or 25 C and the total N₂, fixation over21 d was measured in the absence of a supply mineral N. Alltreatments were subsequently supplied with 10 mmol m^–2NO₂ ^– in the flowing solutions for 14 d, and the relativeuptake of N by N₂, fixation and NO₃ ^– uptake was compared.Net uptake of K⁺ was measured on a daily basis. Root temperature had little effect on root d. wt over the 35-dexperimental period, but shoot d. wt increased by a factor of3.5 between 3 and 25 C, with the sharpest increase occurringat 7–11 C. Shoot: root d. wt ratios increased from 25to 68 with increasing temperature at 7–25 C. N₂-fixationper plant (in the absence of NO₂ ^–) increased with roottemperature at 3–13C, but showed little change above13 C. The ratios of N₂ fixation: NO₂ ^– uptake over 14d (mol N: mol N) were 0.47–0.77 at 3–7 C, 092–154at 11–17 C, and 046 at 25 C, reflecting the dominanceof NO₃ ^– uptake over N₂ fixation at extremes of high andlow root temperature. The total uptake of N varied only slightlyat 11–25 –C (095–110 mmol N plant^–1),the decline in N₂ fixation as root temperature increased above11 C was compensated for by the increase in NO^– ₃ uptake.The % N in shoot dry matter declined with decreasing root temperature,from 32% at 13 C to 15% at 3 C. In contrast, concentrationsof N expressed on a shoot water content basis showed a modestdecrease with increasing temperature, from 345 mol m^–3at 3 C to 290 mol m^–3 at 25 C. Trifolium repens L, white clover, root temperature, N₂ fixation, potassium uptake, nitrate uptake, flowing solution culture     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis II. Morphology and Anatomy of Evolution Forms

Morphological and anatomical parameters which are variable underroot anaerobiosis in Triticum aestivum were checked on fivetaxa of primitive and modern wheats (and the related genus Aegilops).The plants were grown in nutrient solution which was eitheraerated or flushed with nitrogen. When the plants were flushedwith nitrogen a general retardation in longitudinal root growthoccurred in all of them, but only Triticum aestivum showed aclear promotion of growth of later appearing roots enablingit to maintain the same root/shoot ratio even under stress conditions.There was an increase in the volume of intercellular space inthe root cortex of nearly all the plants investigated. The diameterand the lignin content of the roots and the form of their corticalcells also varied. All these changes were expressed in the primitivewheats to a lesser extent than in the advanced Triticum aestivumindicating that there is a clear increase in the adaptive responsein the latter. Triticum species, Aegilops species, wheat, roots, anatomy, anaerobiosis, stress, intercellular space, selection