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.     

Responses to nitrogen sources and regulatory properties of root phosphoenolpyruvate carboxylase

Time course of changes in extractable root phosphoenolpyruvate carboxylase (PEP C) activity was investigated in wheat, barley, and tomato plants fed with different nitrogen sources. Ammonium-fed plants exhibited a 2–2.5-fold higher PEPC activity than nitrate-fed plants at 7 d after the onset of nitrogen supply. Western blot analysis revealed that the amounts of PEPC subunit proteins increased gradually as reflected in the extractable PEPC activity. These results suggest that the increase in PEPC activity may be due to de novo protein synthesis. PEPC was SO-fold purified from tomato roots after several chromatographic steps. Metabolite effects on the partially purified enzyme were also investigated under optimal or suboptimal conditions in terms of pH and concentrations of phosphoenolpyruvate. Organic acids and acidic amino acids inhibited the enzyme activity, while hexose phosphates stimulated it. Glutamine and asparagine produced in the course of ammonium assimilation hardly affected the activity.     

Regulation of mycorrhiza development in durum wheat by P fertilization: Effect on plant nitrogen metabolism

The aim of this work was to study the effect of arbuscular mycorrhizal fungus Glomus mosseae on growth and nitrogen (N) metabolism of durum wheat (Tritcum durum) under various P soil contents. The analyses were extended to macro and micronutrient tissue concentrations, nitrate reductase and glutamine synthetase activities, as well as protein, aminoacids, pyridine dinucleotides and adenine nucleotides. Arbuscular mycorrhiza increased wheat growth in soil in which P availability was low and nitrate was the dominant N form. The root colonization occurred at the highest level in plants grown in limiting soil P and was inversely related to soil P content. The micorrhizal wheat plants contained also the highest concentrations of macro (P, K, Ca, N) and micronutrients (Fe, Zn, Mn) as well as free amino acids, protein, NAD, NADP, AMP, ADP, ATP in roots and leaves. In particular, the micronutrient tissue concentrations (Zn, Mn) supported that mycorrhiza actively modulated their uptake limiting interferences and optimizing growth better than the plant roots, like a very efficient “rootstock”. Control plants grown at the highest soil P did not reach the same concentration as the mycorrhizal plants. Nitrate reductase activities in the roots of mycorrhizal plants were higher than in the control ones, while glutamine synthetase activities were highest in the leaves. Protein and amino acids concentrations, as well as AMP, ADP, ATP, NAD(P), and NAD(P)H were also higher than in the control. Among the free amino acids in the roots, the high levels of glutamine, asparagine, arginine, support the view that ammonium was transferred through the arbuscules to the root cells where it was re‐assimilated in the cortical cells, forming high N : C ratio‐amino acids. They were transferred to the leaves where all the other N compounds could be largely synthesized using the carbon skeletons supplied by photosynthesis.     

Einfluß von N-Lignin auf Wachstum und N-Stoffwechsel von Weizen-Zellsuspensionskulturen

The effects of N-Lignin on growth and N-metabolism in wheat cells in suspension cultures N-Lignin is an organic N-fertilizer which is synthesized from waste liquors of the pulp industry by oxydative ammonisation. Nearly 40% of its N-content is available as ammonium, the rest is linked in organic compounds. Water-soluble fractions of N-Lignin were added to the nutrient solutions of wheat cells in suspension cultures in order to study the effects on growth and N-metabolism. The experiments show that N-Lignin is a suitable nitrogen source for growing wheat cells. The best growth was achieved when 50% of the total nitrogen content of the medium were added as N-Lignin nitrogen. This mixture of N-Lignin and nitrate was even superior to the standard B-5-medium with respect to the final dry weight. However, higher concentrations of N-Lignin inhibited cell growth. The effect of N-Lignin on cell growth is not only influenced by ammonia. If wheat cells were grown on media with ammonium-N as the sole nitrogen source acids of the citrate cycle had to be added to support growth. This was not necessary with N-Lignin. N-Lignin therefore seems to effect the energy metabolism. High amounts of ammonium-N or the reduced N-fractions of N-Lignin respectively resulted in an increase of certain amino acids and especially of the two amides glutamine and asparagine. Furthermore root formation was observed with cells grown in media containing N-Lignin or ammonium-N. The root formation seemed to be correlated with added amounts of reduced nitrogen. Root formation was not observed with cell cultures incubated with N-Lignin solutions which were made free of ammonium-ions with a cation exchanger (Amberlite IR-120) loadad with potassium. This indicates that the differentiation of roots in the normally embryonic cells is due to the ammonium-N content of N-Lignin. A possible correlation between the content of glutamine and asparagine and the formation of roots is discussed.     

可利用的碳和氮对丛枝菌根真菌萌发孢子氨基酸代谢的影响

The effects of carbon (C) and nitrogen (N) sources on N utilization and biosynthesis of amino acids were examined in the germinating spores of the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith after exposure to various N substrates,CO2,glucose,and/or root exudates.The N uptake and de novo biosynthesis of amino acids were analyzed using stable isotopic labeling with mass spectrometric detection.High-performance liquid chromatography-based analysis was used to measure amino acid levels.In the absence of exogenous N sources and in the presence of 25 mL L-1 CO2,the germinating AM fungal spores utilized internal N storage as well as C skeletons derived from the degradation of storage lipids to biosynthesize the free amino acids,in which serine and glycine were produced predominantly.The concentrations of internal amino acids increased gradually as the germination time increased from 0 to 1 or 2 weeks.However,asparagine and glutamine declined to the low levels;both degraded to provide the biosynthesis of other amino acids with C and N donors.The availability of exogenous inorganic N (ammonium and nitrate) and organic N (urea,arginine,and glutamine) to the AM fungal spores using only CO2 for germination generated more than 5 times more internal free amino acids than those in the absence of exogenous N.A supply of exogenous nitrate to the AM fungal spores with only CO2 gave rise to more than 10 times more asparagine than that without exogenous N.In contrast,the extra supply of exogenous glucose to the AM fungal spores generated a significant enhancement in the uptake of exogenous N sources,with more than 3 times more free amino acids being produced than those supplied with only exogenous CO2.Meanwhile,arginine was the most abundant free amino acid produced and it was incorporated into the proteins of AM fungal spores to serve as an N storage compound.     

Growth and chlorophyll,mineral, and total amino acid composition of tomato and wheat plants in relation to nitrogen and iron nutrition II. Chlorophyll content and total amino acid composition

Studies of the amino acids distribution in plants subjected to nutrient regimes are limited. The present study investigated the effect of NO₃‐N and FeSO₄‐Fe regimes on chlorophyll and total amino acids composition of tomato and wheat plants. Also the distribution of 17 amino acids between the different plant parts was studied. Increasing the NO₃‐N level up to 200 mg kg^‐1 greatly increased the total amino acids content of tomato plants. The total amino acids content of wheat plants continued to increase with addition of NO₃‐N up to 400 mg kg^‐1. The response of chlorophyll content to NO₃‐N supply was highly dependent on Fe level both in tomato and wheat plants. The interaction between NO₃‐N and FeSO₄‐Fe had a great effect on the total amino acids content and distribution. Iron increased the translocation of proline from roots to leaves. The overall amino acids contents of leaves was higher than that of stems or roots.     

Availability of several kinds of nitrogenous compounds for the growth of callus tissues from Daucus Carota L., Datura Stramonium L., Pelargonium Inquinans Ait., and Oryza Sativa L.

Plants frequently accumulate or reserve some organic nitrogenous substances of small molecules, when supplied with inorganic nitrogenous compounds in excess. It is well known that rice plants in the field accumulate asparagine when supplied with ammonium salts in excess. This phenomenon is effectively utilized as a criteria for adequate supply of nitrogen fertilizers in the field (1). Accumulation of asparagine has also been generally recognized among seedlings of various plant species grown with excess ammonium, nitrate or urea (2). With rye grass, glutamine was reported to be accumulated in leaves and sometimes excreted when ammonium sulfate was supplied in excess (3). Arginine is a major free amino acid accumulating in nitrogen fertilized apple trees (4), phosphate-deficient mulberries (5), and potassium deficient rice plants (6). Allantoin is known to be a reserve form of nitrogen in some families of higher plants, notably the Aceraceae, Leguminosae and Boraginaceae (7,8). Thus the form of reserve nitrogen compound differs with different plant species.     

Genotypic variation for nitrogen uptake and assimilation using hydroponic culture technique in wheat

Hydroponic culture technique is an alternative way of studying nitrogen metabolism. In this study, the response of six wheat genotypes (PBW 621, PBW 636, GLU 1356, BW 8989, GLU 700, and PBW 343) with respect to nitrogen-metabolizing enzymes in relation to accumulation of soluble proteins and amino acids at two concentrations of nitrogen (2 and 6 mM) was studied. Activities of nitrate reductase (NR) and glutamine synthetase as well as soluble proteins, amino acids, and nitrogen content increased in all six genotypes with increasing concentration of nitrogen in roots as well as shoots. Shoots maintained higher activities of NR and glutamine synthetase; apparently contents of soluble protein, amino acid, and nitrogen were also higher. The upregulation of NR and glutamine synthetase activities with increased concentration of nitrogen possibly contributes to higher nitrogen assimilation efficiency of three genotypes (PBW 621, PBW 636, and GLU 1356) compared to other genotypes.     

Ion chromatographic analysis of selected free amino acids and cations to investigate the change of nitrogen metabolism by herbicide stress in soybean (glycine max)

A simple and reliable method for the determination of NH4+, K+, Na+, aspartic acid, asparagine, glutamine, and alanine by ion chromatography has been developed. It is suitable for monitoring changes of nitrogen metabolism in soybean because it can accurately measure concentrations o asparagine and NH4+, two key substances for nitrogen storage and transport in this plant species Analysis of asparagine distribution in soybean indicated that higher levels (up to 18.4 micromol g(-1) of fresh mass) occur in stems and lower levels in roots (2.0 micromol g(-1) of fresh mass) and leaves (1.6 micromol g(-1) of fresh mass). When the herbicide metsulfuron-methyl (0.5, 5, and 50 ppb) was applied via the nutrient solution to the root system, asparagine concentrations increased 3-6 times in stems roots, and leaves. Metsulfuron-methyl is known to impair the synthesis of branched amino acids and, in consequence, protein synthesis. Thus, nitrogen consumption was limited, leading to ar accumulation of asparagine. The possible use of this physiological response in agricultural practice to identify herbicide stress in soybean and to detect low-level residues of sulfonylurea herbicides ir the soil is discussed.     

The absorption and translocation of amino acids and amides in rice plant

It has been well known that the inorganic nitrogen compounds used as the common nitrogen source for the growth of higher plants can be replaced by some organic nitrogen compounds such as amino acids or amides. According to GHOSH and BURRIS (1), who investigated the effect of some amino acids as the nitrogen source, alanine, asparagine, glutamate and histidine were better nitrogen sources than ammonia for clover and tomato plants. For tobacco, however, nitrate and ammonia were superior to all organic nitrogen compounds used. RATNER et al. (2). made the same kind of study by using corn and sunflower plants and reported that the plants could grow with glycine, aspartate, glutamate and arginine, but all of them were inferior to inorganic nitrogen as the nitogen source.     

Kinetics of 15NH4 + assimilation in tomato plants: evidence for 15NH4 + assimilation via GDH in tomato roots 1

The kinetics of ¹⁵NH₄ ⁺ assimilation into free amino acids and total reduced nitrogen were monitored in both roots and shoots of two week old tomato seedlings supplied with 5 mM 99% (¹⁵NH₄)₂SO₄ via the aerated root medium in hydroponic culture, in the presence and absence of a 2 h pre‐incubation with 1 mM methionine sulfoximine (MSX). The labeling kinetics of amino acids in roots of tomato plants in the presence of MSX show that continued assimilation of ¹⁵NH₄ ⁺ can occur when the GS/GOGAT cycle is inhibited. In the presence of MSX, three amino acids [glutamate, alanine, and y‐amino butyrate (GABA)] of the root tissue continue to become labeled with ¹⁵N under conditions where labeling of the amino‐N moiety of glutamine is completely inhibited. This indicates primary ammonia assimilation via GDH, or alternatively, assimilation of ammonia into alanine via alanine dehydrogenase. Free ammonia accumulates rapidly in both shoots and roots of tomato in response to MSX. The labeled ammonia accumulated in the roots in the presence of MSX must be largely derived from the medium whereas in shoots this ammonia appears to be derived from catabolism of unlabeled amino acids and proteins. The pools of glutamine, glutamate and alanine after 24 h exposure to ¹⁵NH₄ ⁺ were, on the average, 5‐ to 10‐fold lower in the MSX‐treated than in the control (‐MSX) shoots and roots. In contrast, the pools of valine, leucine, isoleucine, proline, threonine, phenylalanine, lysine, and tyrosine increased 5‐ to 10‐fold above the control values in the shoots of MSX‐treated plants, and 2‐ to 4‐fold above control values in the roots of MSX‐treated tomato plants after 24 h. The latter amino acids all exhibited low isotope abundance, and presumably were derived from protein turnover.     

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 assimilation in sunflower leaves and upward and downward transport of nitrogen

The assimilation of ammonium and nitrate nitrogen into amino acids of mature sunflower leaves and their transport to the other plant parts were investigated using nitrogen-15 as a tracer. In the leaf, to which ¹⁵N-labelled ammonium was vacuum-infiltrated, the ¹⁵N content of glutamine was always the highest of the amino acids tested and that of alanine was higher than that of glutamic acid and aspartic acid at 15 min after the infiltration. On the other hand in the leaf to which ¹⁵N-labelled nitrate was vacuum-infiltrated, the ¹⁵N content of glutamic acid and aspartic acid was superior to that of glutamine. The incorporation of ¹⁵N into serine was not active in the case of either ¹⁵N-labelled ammonium or nitrate. In the internodes above and below the treated leaf, through which photosynthates were transported into other parts, the ¹⁵N content of γ-aminobutyric acid and glutamine was markedly high when both nitrogen sources were supplied. There were no differences in the labelling patterns of amino acids between the upper and lower internodes. From these results it may be concluded that glutamine, glutamic acid, and aspartic acid play an important role in the assimilation of ammonium and nitrate nitrogen in leaves and that nitrogen is transported mainly in the forms of γ-aminobutyric acid and glutamine from the leaves to the other plant parts,     

Amino acids exuded from axenic roots of lettuce and white lupin seedlings exposed to different cadmium concentrations

The objective of this study was to evaluate if amino acids in roots and/or in root exudates play a role in cadmium (Cd) stress. Lettuce (Lactuca sativa L. cv. Reine de Mai) and white lupin (Lupinus albus L. cv. lublanc) were grown for 19 to 21 days with axenic roots in a hydroponic system. After treatment with various concentrations of Cd (0, 0.01, 0.1, 1, 10, and 100 μM Cd) per nine days, roots and root exudates were collected. The stress did not result in significant dry weight (DW) differences between Cd‐treated and control plants, but Cd induced decreases in relative water content (RWC) and water potential (Pm). Amino acid levels and carbon (¹⁴C) incorporation into amino acids increased at low Cd concentrations in roots. However, 100 μM Cd induced a decrease of amino acid levels and an equally significant reduction of ¹⁴C incorporation, suggesting a decreased plant metabolism. Moreover, a higher Cd concentration induced increased levels of specific amino acids, for instance asparagine and lysine in lettuce and asparagine and hydroxylysine in lupin roots. Amino acids in root exudates corresponded less than 1% of the amounts found in root cells suggesting that amino acids could not be the major Cd chelators. Amino acid accumulation in root exudates differed than that found in roots except for asparagine. In conclusion, Cd induces in the root and root exudates increased levels of specific amino acids, such as Asn, Lys and HLys similarly to other environmental stresses. Although the amino acids could not participate in Cd chelation, lysine and its derivatives, such as hydroxylysine, could be used as stress markers for Cd in higher plants.     

麦套花生氮素代谢及相关酶活性变化研究

大田条件下,以花生“花育22号”为材料,研究了麦套花生的氮素代谢及相关酶活性变化情况。结果表明,麦套花生根叶游离氨基酸、氮素平均含量及根系可溶性蛋白平均含量高于单作;而叶片可溶性蛋白平均含量则低于单作。与小麦共生期间,麦套花生根叶硝酸还原酶（NRase）活性、谷氨酸脱氢酶（GDH）活性、叶片谷氨酰胺合成酶（GS）活性及谷氨酸-丙酮酸转氨酶（GPT）活性（除播后25 d）明显低于单作;整个生育期麦套花生根系GS平均活性及GPT活性高于单作花生。可见,花生苗期小麦遮荫对花生氮素代谢及酶活性有一定影响。     

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).     

Potential Nitrate Leaching Under Common Landscaping Plants

Two Elsholtzia haichowensis S. populations, copper-tolerant (TLS) and non-tolerant (HA) ones were studied in hydroponic experiment for the nitrogen assimilation and plant growth under excess Cu conditions. The results demonstrated that there were surely the differences in nitrogen assimilation and plant growth between the two populations. Excess Cu caused evident decreases in the shoot and root biomass and root/shoot biomass ratio in HA population while no significant changes happened in TLS population. In addition, in HA population, excess Cu also induced apparent declines in activities of nitrate reductase (NR, EC 1.6.6.1) and glutamine synthetase (GS, EC 6.3.1.2) in the leaves and roots as well as the contents of nitrate, ammonium and amino acids in the roots. In TLS population, excess Cu did not significantly affect the NR activities in the leaves and roots and the nitrate content in the roots, and apparently elevated the root ammonium and amino acids contents, although it also clearly reduced the GS activities in the leaves and roots. Besides, with the addition of Cu in the culture solution, the Cu contents in the leaves and roots of the two populations markedly increased. But this increase was significantly lower in TLS population than that in HA population; the fact might be partly responsible for the relative stabilization of nitrogen assimilation in TLS population compared to that in HA population.     

Response of wheat and maize to different nitrogen sources: II. Nitrate reductase and glutamine synthetase enzyme activities,and plastid pigment content

Glutamine synthetase and nitrate reductase enzyme activities occurred both in roots and leaves of maize (Zea mays L., hybrid Pioneer 3737) and wheat (Triticum aestivum L., cultivar Jantar) plants grown on different nitrogen (N) sources. Enzyme activities and plastid pigment content in maize plants were higher in the treatments with a mixture of nitrate (NO₃) and ammonium (NH₄) than with either N source alone. In wheat plants, plastid pigment content, nitrate reductase activity, and root glutamine snynthetase activity were higher in the treatments where NO₃ alone was applied to the nutrient medium.     

Stickstoff-Assimilation in der Wurzel und Transport von N-Verbindungen mit dem Blutungssaft der Wurzeln in Abhängigkeit von der Mn-Versorgung

Nitrogen Assimilation in Roots and the Transport of Nitrogen Compounds in the Bleeding Sap of Roots in relation to Manganese Nutrition. The assimilation of nitrogen in the roots of 27 days old pumpkin plants was examined in relation to manganese nutrition. The transport of nitrogen compounds in the xylem was determined in roots and in the bleeding sap of roots using nitrate as the N-source. The maximum NO₃ content in the roots was observed in the Mn treatment which resulted in the highest shoot yields (0.05 ppm Mn). The bleeding sap of this treatment was lowest in nitrate concentration, but showed the highest rate of transport of organic nitrogen compounds. In experiments with ¹⁵N in the nutrient solution the isotope was found in the roots in organic and in inorganic compounds. The composition of the fraction of free amino acids differed between roots and xylem sap. In the bleeding sap glutamine was especially dominant. In the roots the amino acid composition depended on the extent of Mn-supply. Lowest glutamine concentrations were found in the xylem sap from the treatment with maximum shoot yields. A numerical difference was found in the xylem sap between organic N (N_(org)) and the amino acid nitrogen. This difference which account for more than 50 % of the organically bound nitrogen is suggested to be made up in part by low molecular weight peptides, amino sugars and other compounds. In Mn deficiency a general reduction in the intensity of nitrogen metabolism was found. With Mn toxicity the N assimilation activity was more intensive than for the low Mn supply. Simultaneously, however, the transport of organic N compounds from the root was lower.     

Der Einfluß der Kalium-Ernährung auf den Gehalt und das Spektrum löslicher Aminoverbindungen in Rotklee (Trifolium pratense L.)

Effect of potassium nutrition on the content and the spectrum of soluble amino compounds in Red Clover 1. A better K nutrition of Red Clover (Trifolium pratense) resulted in higher contents of soluble amino acids of the upper plant parts. The plants of the treatment with the highest K application showed nearly double as high contents of glutamic acid, aspartic acid, alanine and γ-aminobutyric acid than the plants of the K₀ treatment. The content of asparagine was not as much affected by the K nutrition and the content of glutamine was even lowered. 2. Red Clover responded on the K treatment with its content of soluble amino compounds quite different than non leguminous plant species which show decreasing contents of soluble amino acids with an increasing K nutrition. Therefore it is concluded, that the K nutrition of legumes affects the N₂-fixation of Rhizobium leguminosarum. 3. The higher contents of soluble amino compounds did not influence the protein content of the upper plant parts. But with the better K supply the yields were increased considerably and therefore also higher yields of proteins were harvested. Very low K supply resulted in a high protein content, due to an inhibition of plant growth.