Amino acid metabolism in plant leaf

¹⁴C-labelled sodium bicarbonate and ¹⁵N-labelled ammonium sulfate were simultaneously vacuum-infiltrated into detached sunflower leaves, and the incorporation of ¹⁴C and ¹⁵N into free amino acids was chased during 60-min period in the light and in the dark.

In the light, the ue specific activity of aspartic acid, alanine, serine and glycine rapidly increased for 5 min and thereafter decreased. On the other hand, that of gultamic acid continued to increase slowly during the entire 60-min period. In the dark, aspartic acid most actively incorporated ¹⁴C. The difference of changes in ¹⁴C specific activity between glutamic acid and other amino acids was also observed in the dark as in the light. These results suggest that the carbon skeleton of glutamic acid is synthesized from aspartic acid, alanine, serine and glycine.

¹⁵N content of glutamine was the highest of all amino acids investigated in the light, and it was followed by glutamic acid. alanine, aspartic acid, serine and glycine, in this order. In the dark, ¹⁵N content of glutamic acid fell remarkably and was lower than that of alanine up to 5 min. From these ¹⁵N tracer experiments, it is suggested that the incorporation of ammonium into glutamic acid is strictly dependent on light and that alanine incorporates ammonium by the direct amination besides the transamination from glutamic acid.     

Natural abundance of 15N in nitrate,ureides, and amino acids from plant tissues

The natural ¹⁵N abundances (δ¹⁵N values) were measured for nitrate and free and bound amino acids from the leaves of field-grown spinach (Spinacia oleracea L.) and komatsuna (Brassica campestris L.), as well as ureides and free and bound amino acids in the leaves and roots of hydroponically grown soybean (Glycine max L.) totally depending on dinitrogen. Nitrate from the spinach and komatsuna leaves and ureides from leaves and roots of soybean showed higher δ¹⁵N values than the total tissue N and N in free or bound amino acid fractions. The δ¹⁵N values of individual free and bound amino acids, determined by GC/C/MS using their acetylpropyl derivatives, were similar in leaf tissues except for proline but varied in soybean root tissues. The order of ¹⁵N enrichment was similar in the four samples: aspartic acid > glutamic acid > threonine, proline, valine > glycine + alanine +serine, γ-amino butyric acid, and phenylalanine.     

Incorporation of 15N into various nitrogenous compounds in intact soybean nodules after exposure to 15N2 gas

The intact nodules attached to the upper part of soybean roots were exposed to ¹⁵N₂ and the incorporation of ¹⁵N into various soluble nitrogen constituents was investigated. Results indicated that ammonia, a primary product of N₂ fixation, was located in more than two compartments. Ammonia reduced from N₂ gas seemed to be incorporated firstly into glutamine especially amido-group nitrogen. Newly fixed nitrogen was secondly incorporated into glutamic acid and alanine in this sequence. These results suggested that fixed ammonia was assimilated by glutamine synthetase/glutamate synthase pathway. Turn-over rate of allantoin plus allantoic acid and serine was relatively high, although apparently these compounds were not primary products of newly fixed ammonia. ¹⁵N content of allantoin was always higher than that of allantoic acid. ¹⁵N incorporation to aspartic acid and asparagine was relatively slow, especially in early period. In bacteroid fraction there is much amount of ammonia comparing with other compounds, while allantoin and asparagine were presented exclusively in cytosol. ¹⁵N was incorporated into nitrate within a few minutes especially in bacteroids.     

Ammonium assimilation in rice based on the occurrence of 15N and inhibition of glutamine synthetase activity

Assimilation of ammonium (NH₄) into free amino acids and total reduced nitrogen (N) was monitored in both roots and shoots of two‐week old rice seedlings supplied with 5 mM 99% (¹⁵NH₄)₂SO₄ in aerated hydroponic culture with or without a 2 h preincubation with 1 mM methionine sulfoximine (MSX), an inhibitor of glutamine synthetase (GS) activity. ¹⁵NH₄ was not assimilated into amino acids when the GS/GOGAT (glutamate synthase) cycle was inhibited by MSX. Inhibition of glutamine synthetase (GS) activity in roots with MSX increased both the amount of NH₄ and the abundance of ¹⁵N labeled NH₄. In contrast, the amount of Gln and Glu, and their proportions as ¹⁵N, decreased in roots when GS activity was inhibited. This research confirms the importance of GS/GOGAT in NH₄ assimilation in rice roots.

¹⁵N‐labeled studies indicate that NH₄ ions incorporated by roots of rice are transformed primarily into glutamine (Gln) and glutamic acid (Glu) before being converted to other amino acids through transamination (15). The formation of amino acids such as aspartic acid (Asp) and alanine (Ala) directly from free NH₄ in roots also has been reported (4,15). Translocation of free NH₄ to plant shoots, based on the concentration of free NH₄ in xylem exudate, has been reported in tomato (13), although NH₄ in shoots primarily originates from nitrate reduction in the shoot. Photorespiration also can contribute to the accumulation of NH₄ in leaves (7).

The GS/GOGAT cycle appears to be primarily responsible for the assimilation of exogenously supplied NH₄ and NH₄ derived from nitrate reduction in leaves, as well as NH₄ derived from photorespiration (2,3,6,8). Genetic evidence cited to support this conclusion includes the lethal effect of photorespiratory conditions on plant mutants deficient in chloroplast‐localized GS and GOGAT activities (2,3,9), and the rapid accumulation of free NH₄ in GS‐deficient mutants under photorespiratory conditions (2,3,5).

The present study was initiated to quantify the in vivo amino acid synthesis in rice roots and shoots by analysis of ¹⁵N labeling, and should provide a more complete understanding of this important system for NH₄ utilization.     

Nitrogen nutrition and growth of the rice plant

Rice seedlings were pulse-labelled with ¹⁵N by feeding ¹⁵N-labelled KNO₂ through culture solution and ¹⁵N translocation in the plant was chased.

¹⁵N incorporated into older leaves was retranslocated to the youngest leaf. Nitrogen of newly developing leaves consisted of the newly absorbed and retranslocated nitrogen.

Retranslocation of nitrogen seemed to occur from the older leaves than the second leaf below developing leaf although those older leaves had no significant change in total nitrogen content.

Whole protein in developed leaves had the half-life of 4-6 days, and the protein seemed to be consisted of proteins of different turnover rates.     

钙螯合剂对小麦幼苗氮代谢和干物重的影响

营养液中添加钙螯合剂EGTA[Glycol bis ( aminoethyl)etherN ,N ,N ,N tetraaceticacid ,乙二醇双 (-氨基乙基 )醚四乙酸 ]导致小麦幼苗干物质累积下降 ,降低地上部和地下部全钙含量 ,抑制小麦幼苗对外源硝态氮的吸收及其向地上部的运输 ,改变其在不同器官中的分配比例和影响其向氨基氮或可溶性蛋白质的转化。叶片和根中硝酸还原酶活性与相应器官中的NO3--N含量相关 ,叶片中谷氨酰胺合成酶 (GS)活性在EGTA处理后明显下降 ,根中GS活性变化不显著。     

Comparative effects of app1ication of coated and non-coated urea in clayey and sandy paddy soi1 microcosms examined by the 15N tracer technique

Abstract

¹⁵N assimilation was studied in bacteroid and cytosol fractions of soybean nodules. In the first experiment, after exposing the intact nodules to ¹⁵N₂ for 5 min and 10 min, most of the fixed ¹⁵N was detected in cytosol fraction. In cytosol fraction, ¹⁵N content of glutamine was the highest and followed by glutamic acid, alanine, and allantoin in this sequence, whereas, in bacteroid fraction, glutamic acid showed the highest ¹⁵N content and alanine and glutamine followed. In the second experiment, ¹⁵N assimilation of various ¹⁵N-labeled compounds in the separated bacteroid and cytosol fractions was investigated. In the separated bacteroid fraction which was fed with ¹⁵NH₄, ¹⁵N was incorporated very rapidly into glutamic acid, alanine, and aspartic acid, but very slowly into glutamine.

From these results, it was suggested that most of the fixed ammonia was exported to cytosol and assimilated via glutamine synthetase to glutamine, then via glutamate synthase to glutamic acid, and from these compounds various nitrogenous compounds were formed, but in bacteroids glutamate dehydrogenase and alanine dehydrogenase played an important role in the assimilation of fixed ammonia though quantitatively the contribution to ammonia assimilation in nodules was much less compared with cytosol.     

Amino acid metabolism in plant leaf

Recent studies have shown that the incorporation of ammonium nitrogen into amino acids in the leaves is strictly dependent on light (1-4). It is speculated that the effect of light on ammonium assimilation may be through the synthesis of the precursors of amino acids, or by the supply of the energy required for amination and amidation with organic acids. In the Vicia faba chloroplasts Givan et al. (1) exhibited that the synthesis of glutamic acid from a-ketoglutarate was linked with the generation of reduced pyridin nucleotide by photosynthetic electron transport. Mitchell and Stocking (2) suggested the direct coupling of glutamine formation with photophosphorylation in the pea chloroplasts. On the other hand. the processes of nitrate assimilation are more indebted to light than those of ammonium assimilation, because the former ones involve the reduction of nitrate to ammonium which is believed to be light-dependent (5). Canvin and Atkins (6). and Atkins and Canvin (7) reported that the incorporation of ¹⁵N-labeled ammonium and nitrate into amino acid fractiom was depressed by the dark treatment and by photosystem inhibitors; 3-(3′,4′-dichlrophenyl)-1-1-dimethylurea (DCMU) and carbonyl-cyanide-m-chlorophenyl-hydrazone(CCCP).     

15N study on the partitioning of the nitrogen taken by soybeans from atmospheric dinitrogen,medium nitrate or ammonium

Abstract

Soybean plants (Glycine max, cv. Akisengoku) were water-grown in a greenhouse with a low concentration of nitrate in the culture solution. Under these conditions root nodulation mostly on primary roots was profuse. At the vegetative and pod-filling stages, plants were fed ¹⁵N-labeled dinitrogen, nitrate, or ammonium for 7 to 8 hr in the daytime.

Partitioning of the ¹⁵N from the three nitrogen sources showed distinct characteristics. The nitrogen (N) from dinitrogen preferentially distributed to the developing organs, young leaves, and developing pods, in comparison with N from nitrate. N from ammonium showed distribution pattern similar to that of N from dinitrogen.

The nodule N was supplied by both directly fixed-N and transferred nitrogen, and fixedN was inferred to play a major role in this process. The pro tein N in the roots could be furnished by the recycled N of dinitrogen and nitrate through the shoots along with direct incorporation of amino acids produced in the roots from nitrate     

The uptake,distribution, and accumulation of 15N-labelled ammonium and nitrate nitrogen top-dressed at different growth stages of rice

A pot experiment with soil culture was carried out to trace ¹⁵N-labelled nitrogen top-dressed at different growth stages of rice. The study involves the use of a modified vacuum system for determining total nitrogen by gu volumetric measurement, and the N₂ gas sampled in the discharge tube was analysed for nitrogen-15 by the optical spectrographic technique.

The plants took up more nitrogen from (¹⁵NH₄)₂SO₄ than from Na¹⁵NO₃, irrespective of the stage of dressing, and the uptake of both forms was much higher when the planta were top-dressed at the young panicle formation stage as compared with the later dressings. At full maturity the plants had the highest accumulation of labelled nitrogen from both ammonium and nitrate sources when they are top-dressed at the young panicle formation stage. More than 80% ot the labelled nitrogen taken up by the plants waa distributed in the brown rice and this trend was more remarkable when top-dressing was carried out at the milk stage. The distribution patterns of ammonium and nitrate nitrogen were similar in brown rice but differed in leaves and stem.

Nitrogen transported from other parts to the panicle was utilized for the formation ot the husk until the booting stage, and then for brown rice development. With the completeness of husk formation, at the milk stage, nitrogen transported to the grain might have been utilized for brown rice development more rapidly. In the brown rice, nitrogen from ammonium was translocated maximally to the inner part of the endosperm from dressing at the booting stage, and to the embryo from that at the milk stage, whereas that from nitrate was translocated maximally to the embryo from the dressings at both stages.     

Nitrogen transformations of ammonium sulfate and alanine in submerged Maahas clay

The fate of added nitrogen in submerged soils was studied using ¹⁵N-labelled ammonium sulfate and alanine. After 8 weeks of incubation 25 and 22%, respectively, of nitrogen from ammonium sulfate and alanine were recovered in the soil. Under the experimental conditions used nitrogen added to presubmerged soils was lost rapidly outside of the soil-water system, regardless of whether the nitrogen was organic or inorganic. Fractionation studies revealed that the amount of tagged N incorporated into exchangeable ammonium, residual fractions, volatilized as NH₃ and chemically fixed nitrogen was not enough to account for the nitrogen loss. The nitrogen loss was attributed to nitrification and subsequent denitrification during the incubation period.

The effect of N-Serve [2-chloro-6-(trichloromethyl)pyrimidine] on nitrification of ¹⁵N-labelled (NH₄)₂SO₄-in submerged soils was studied. About 15% more nitrogen was recovered from non-presubmerged soils, and less nitrate was accumulated in presubmerged soils where N-Serve coated (NH₄)₂SO₄ was applied, than from soils where (NH₄)₂SO₄ was applied without N-Serve. Presubmerged soils provided a more favorable environment for nitrification than for denitrification under the experimental conditions used.     

Nitrogen Uptake and Allocation in Sweet Viburnum During a Root Growth Flush

Most woody ornamentals exhibit episodic growth flushes and nitrogen (N) uptake has also been demonstrated to be seasonal. However, there is little information on N uptake in relationship to plant growth cycle. In this study, N uptake and allocation of sweet viburnum during periods of low and high root elongation rates were studied. Plants were fertilized with ammonium nitrate (¹⁵NH₄ ¹⁵NO₃) and after 6 d N absorption was determined. Significantly more N was absorbed by plants with low root elongation rate compared with plants with high root elongation rate. About 70% of the N absorbed by plants with low root elongation rate was allocated to the mature leaves compared to 35% on plants with high root elongation rate. It was evident that root growth activity influenced N absorption and allocation. Although only a small amount of the N absorbed by plants with low root elongation rates was allocated to the immature leaves, significantly more N was allocated to the immature leaves by plants with high root elongation rates. It is possible that the N necessary to support immature leaf growth, when root elongation rate is low, is provided by mobilization from other parts, possibly mature leaves.     

Elevated CO2 concentrations increase leaf nitrate reduction by strengthening sink activity in soybean plants

An experiment was conducted to examine the effect of CO₂ enrichment on the nitrate uptake, nitrate reduction activity, and translocation of assimilated-N from leaves at varying levels of nitrogen nutrition in soybean using ¹⁵N tracer technique. CO₂ enrichment significantly increased the plant biomass, apparent leaf photosynthesis, sugar and starch contents of leaves, and reduced-N contents of the plant organs only when the plants were grown at high levels of nitrogen. A high supply of nitrogen enhanced plant growth and increased the reduced-N content of the plant organs, but its effect on the carbohydrate contents and photosynthetic rate were not significant. However, the combination of high CO₂ and high nitrogen levels led to an additive effect on all these parameters. The nitrate reductase activity increased temporarily for a short period of time by CO₂ enrichment and high nitrogen levels. ¹⁵N tracer studies indicated that the increase in the amount of reduced-N by CO₂ enrichment was derived from nitrate-N and not from fixed-N of the plant. To examine the translocation of reduced-N from the leaf in more detail, another experiment was conducted by feeding the plants with ¹⁵NO₃-N through a terminal leaflet of an upper trifoliated leaf under depodding and/or CO₂ enrichment conditions. The export rate of ¹⁵N from the terminal leaflet to other plant parts decreased by depodding, but it increased by CO₂ enrichment. CO₂ enrichment increased the percentage of plant ¹⁵N in the stem and / or pods. Depodding increased the percentage of plant ¹⁵N in the leaf and stem. The results suggested that the increase in the leaf nitrate reduction activity by CO₂ enrichment was due to the increase of the translocation of reduced-N from leaves through the strengthening of the sink activity of pods and / or stem for reduced-N.     

Effects of Soil Application of Amino Acids,Ammonium, and Nitrate on Nutrient Accumulation and Growth Characteristics of Sweet Basil

ABSTRACT

The use of organic or reduced form of nitrogen (N) can have various beneficial effects in terms of plant nutrient uptake, metabolism, and environmental issues. In this study, the influence of soil application of reduced N-forms (ammonium, glycine, and glutamine) compared to nitrate and a no fertilizer treatment was evaluated on growth characteristics of sweet basil (Occimum basilicum L.) under a moderate lime soil conditions. The basil growth traits including root and shoot biomass were increased under application of reduced N-forms mainly glycine and glutamine compared to no fertilizer treatment. Application of reduced forms of nitrogen (ammonium, glycine, and glutamine) increased the leaf concentrations of potassium (K), magnesium (Mg), calcium (Ca), iron (Fe) and zinc (Zn), whereas the leaf N concentration was increased by ammonium and nitrate fertilization compared to unfertilized control plants. The results indicate that soil application of reduced N-forms particularly glycine and glutamine is superior to nitrate application.     

设施栽培油桃对叶面施15N的吸收、分配特性研究

以设施栽培的5年生早红珠油桃/山毛桃为试材,应用15N示踪技术研究油桃叶片对15N-尿素的吸收及运转特性。结果表明,叶片施用15N-尿素标记叶吸收主要发生在叶片涂抹15N-尿素后6.h内,平均吸收速率为0.204mg/(g.h);标记叶中15N吸收量24.h达到最高,新梢和梢顶嫩叶15N含量在施用15N-尿素48.h达到最高,下部叶15N含量很低,没有明显的峰;处理168.h各器官中15N含量为标记叶梢顶嫩叶新梢下部叶;试验结束时分配势Ndff(即各器官N含量来自化肥N所占的百分率)为标记叶中最高,然后依次为梢顶嫩叶、新梢、下部叶。这说明氮素迅速被吸收并运到嫩梢和嫩叶中,从而促进这些新生器官的形态建造,可起到以N增C的作用。不同叶面处理的试验还表明,正面和背面全部涂抹的叶片15N含量最高,只涂抹叶片背面次之,涂抹正面最低。设施栽培油桃叶片可迅速吸收尿素,其吸收量早晨明显优于中午和下午,因此设施油桃栽培管理中于早晨进行叶面施尿素,且正反面兼顾,N素的吸收利用效果最好。     

Growth response and nitrogen metabolism of sunflower (Helianthus annuus L.) to vermicompost and biogas slurry under salinity stress

Sunflower was grown under saline media with or without vermicompost amendment and biogas slurry, the organic fertilizers. A randomized complete block design with five replications was used. Forty-five pots were divided in three sets comprising of 15 pots each. Out of 15 pots of each sets, five pots of each were subjected to different levels of saline water irrigation i.e. electrical conductivity (EC): 0.5, 4.8 8.6 dS/m). Amendments of vermicompost and biogas slurry have shown some reduction of sodium induced inhibitory effects. Analyses of fresh and dry weight of leaves, ions, amino acid, protein and nitrogen metabolism enzymes in leaves etc., have been undertaken with reference to above-mentioned treatments. Organic manure amendments improved growth yield, nitrate and protein content and decreased the amount of sodium (Na⁺), chloride (Cl^?), ammonium and total amino acid under saline or non-saline condition. Activities of nitrogen (N)-assimilating enzymes i.e. nitrate reducatse (NR, EC 1.6.6.1), nitrite reductase (NiR, EC 1.6.6.4), glutamine synthetase (GS, EC 6.3.1.2) and glutamate synthase (NADH-GOGAT, EC 1.4.1.14) were enhanced to some extent irrespective to non saline or saline condition. Under salinity NADH-glutamate dehydrogenase (GDH, EC 1.4.1.2) activity was stimulated concomitantly with the increasing ammonium contents and proteolysis activity in the leaves and organic manure did not show a significant difference as compared to their respective control. With respect to salt stress, among the two above-mentioned organic manure, vermicompost showed better result in the entire studied parameter as compared to the biogas slurry.     

Immobilization and remineralization of N following addition of wheat straw into soil: determination of gross N transformation rates by N-ammonium isotope dilution technique

N dynamics in soil where wheat straw was incorporated were investigated by a soil incubation experiment using ¹⁵N-labelled nitrate or ¹⁵N-labelled wheat straw. The incubated soils were sampled after 7, 28, 54 days from the incorporation of wheat straw, respectively, and gross rates of N transformations including N remineralization and temporal changes in the amount of microbial biomass were determined.Following the addition of wheat straw into soils, rapid decrease of nitrate content in soil and increase of microbial biomass C and N occurred within the first week from onset of the experiment. Both the gross rates of mineralization and immobilization determined by ¹⁵N-ammonium isotope dilution technique were remarkably enhanced by the addition of wheat straw, and gradually decreased with time. Remineralization rate of N derived from ¹⁵N-labelled nitrate, and mineralization rate of N derived from ¹⁵N-labelled wheat straw was estimated by ¹⁵N isotope dilution technique using non-labelled ammonium. Remineralization rates of N derived from ¹⁵N-labelled nitrate were calculated to be 0.71 mg N kg⁻¹ d⁻¹ after 7 days, 0.55 mg N kg⁻¹ d⁻¹ after 28 days, and 0.29 mg N kg⁻¹ d⁻¹ after 54 days.Nearly 10% of the ¹⁵N-labelled N originally contained in the wheat straw was held in the microbial biomass irrespective of the sampling time. The amount of inorganic N in soil which was derived from ¹⁵N-labelled wheat straw ranged between 1.93 and 2.37 mg N kg⁻¹.Rates of N transformations in soil with ¹⁵N-labelled wheat straw were obtained by assuming that the k value was equal to the ¹⁵N abundance of biomass N, and the obtained values were considered to be valid.     

Absorption,translocation, and assimilation of foliar-applied urea compared with nitrate and ammonium in tomato plants

To evaluate the use of foliar application of N fertilizer and the occurrence of leaf injury in tomato plants (Lycopersicon esculentum Mill., cv. Momotaro), the effects of the form and concentration of N and solution pH on the leaf injury were studied in the first experiment (Expt. 1). The effects of solution pH and leaf surface on the absorption, translocation, and assimilation of urea were compared with those of nitrate and ammonium in the second experiment (Expt. 2). In Expt. 1, no leaf injury was observed regardless of N sources applied at the N concentration of 1.0 g L^-1. Compared with nitrate or ammonium, the index of leaf injury was the lowest in the leaf to which urea had been applied (hereafter referred to as “urea-applied leaf”), when the N level increased from 2.0 to 10.0 g L^-1. Leaf injury was not affected by the solution pH in the case of urea, but it increased in the case of ammonium and decreased when nitrate was applied with increasing solution pH. In Expt. 2, the absorption of nitrate and ammonium by a leaf within 4 d was 34% and 74% of that of urea, respectively. N absorption at the lower leaf surface was much greater than that at the upper leaf surface for each N source. No apparent effect of solution pH on the absorption of urea was detected. With increasing solution pH, however, the absorption of nitrate decreased. The absorption of ammonium was the greatest at solution pH 7.5. Total-¹⁵N translocation from applied leaf to other plant parts within 4 d was the largest in the urea-applied plants. Effects of solution pH and leaf surface on ¹⁵N distribution were not appreciable. ¹⁵N assimilation was the quickest in the urea-applied plants. Two days after application, ¹⁵N assimilation in the whole plant was up to 76.9% in the urea-applied plants, but only 33.7% and 43.0% in the nitrate- and ammonium-applied plants, respectively. Urea was an appropriate foliar N source due to the low ability to injure foliage because of the rapid absorption and translocation, fast assimilation, and the wide and suitable range of solution pH. Foliar application of N to the lower leaf surface was recommended.     

Provision of carbon skeletons for amide synthesis in non-nodulated soybean and pea roots in response to the source of nitrogen supply

Abstract

Soluble amino acids in roots and primary amino acids, which were involved in primary ammonium assimilation, in the metabolites of ¹⁴C-glucose fed to roots for 3 h in the dark were analyzed in the roots of non-nodulated soybean and pea plants grown in ammonium, nitrate or nitrogen-free media for 1 day. Compared with the effect of nitrate, ammonium supply strongly affected the content and synthesis of the amino acids in the roots. In both soybean and pea roots, the supply of ammonium increased considerably the concentrations of the primary amino acids, and asparagine was the most predominant amide, followed by glutamine. In nitrate-supplied soybean roots, the concentrations of asparagine, aspartate and alanine increased, but the concentration of glutamine was low. In the roots of pea plants grown in nitrate media, asparagine was the predominant amino acid, although the composition of the primary amino acids was little affected by nitrate supply. The proportion of amino acids synthesized from ¹⁴C-glucose increased and asparagine rather than glutamine was predominantly synthesized in ammonium-supplied soybean and pea roots, whereas in nitrate-supplied roots asparagine was more actively synthesized than glutamine, although asparagine was not predominant. The ratio of C4 (asparagine + aspartate) to C5 (glutamine + glutamate) amino acids was twofold higher in ammonium-supplied and nitrate-supplied soybean roots than in roots receiving no nitrogen. In contrast, in pea roots, the C4/C5 ratio was twofold higher only in ammonium nutrition. The results obtained suggest that the roots of leguminous plants might possess an indigenous ability to provide a carbon skeleton for preferential synthesis of asparagine rather than glutamine with a high intensity of ammonium supply.     

Lettuce (Lactuca sativa L.) growth,yield and quality response to nitrogen fertilization in a non-circulating hydroponic system

The objective of this study was to determine the effect of nitrogen fertilization rate on growth and quality of leafy lettuce grown during the winter season in non-circulating hydroponic system. Plants were subjected to seven nitrogen (N) concentrations, i.e. 0, 30, 60, 90, 120, 150 and 180 mg L^?1 N using ammonium nitrate. Nitrogen treatments did not have a significant effect on leaf fresh and dry mass, root fresh and dry mass, number leaves and leaf area. Leaf ascorbic acid and total phenolic content, and antioxidant capacity peaked at 100 and 120 mg L^?1 N, whereas leaf chlorophyll concentration linearly increased with increasing N application. The results indicate that a solution N concentration of 100 and 120 mg L^?1 may be sufficient to improve growth, yield and quality parameters of leafy lettuce grown in non-circulating hydroponic system.