Low phosphate nutrition alters bean plants’ ability to assimilate and translocate nitrate

Bean plants (Phaseolus vulgaris L.) were cultured for 10 or 18 days on phosphate sufficient (+P) or phosphate deficient (‐P) nutrient medium. Nitrate and phosphate distribution between shoot and root, nitrate uptake, and nitrate reductase activity (NR activity, in vivo and in vitro) in root and leaves was estimated. The decrease in Pi concentration in leaves and roots led to decreased rate of NO₃ uptake and increased NO₃ accumulation in roots, accompanied by alterations in NO₃ distribution between shoot and roots. Nitrate reductase activity estimated in vitro was twice higher than estimated in vivo and both in +P and ‐P plants was lower in the roots than in the shoots. The decrease of NR activity in ‐P plants was more pronounced in the roots and after 2 weeks of phosphate starvation it was about 40% lower as compared with the control. The depression in nitrate uptake may be the result of feedback inhibition due to accumulation of nitrate in the roots. The increased NO₃ concentration in root tissue may be explained by decreased NR activity and lower transport of nitrate from roots to shoot.     

Nitrogen Metabolism in Tomato Plants Under Cadmium Stress

Abstract

Young seedlings of tomato (Lycopersicon esculentum Mill.) grown on nitric medium and treated with different cadmium (Cd) concentrations (0–50 µM) were used. Results obtained show that Cd remains predominantly located in the roots, which then seem to play the role of trap‐organs. Increasing Cd concentration in the medium leads particularly to a decrease in NO₃ ^? accumulation, together with decrease in the activities of nitrate reductase (NR), nitrite reductase (NiR), and glutamine synthetase (GS). On the other hand, stimulations were observed for ammonium accumulation, anabolitic activity of glutamate dehydrogenase (GDH) and protease activity. Contrarily, decreases were obtained for soluble protein contents and catabolitic activity of GDH. These results were discussed in relation to the hypothesis attributing to the mitochondrial enzyme NADH‐dependent GDH, an important role in the plant defense processes, in maintaining the glutamate pool in conditions where the need for NH₄ ⁺ detoxification is increased by heavy metals.     

Effects of atmospheric nitrogen dioxide on uptake and assimilation of ammonium in soybean plants

Twelve‐day‐old soybean plants were supplied with 1 mM ammonium chloride (NH₄C1) to roots and exposed to 0.2–0.25 μL.L^‐1 nitrogen dioxide (NO₂) for seven days. Amount and rate of ammonium uptake were decreased by NO₂ exposure. However, the ammonium concentration in leaves and leaf pH of exposed plants were increased by NO₂ exposure. These results suggest that the decrease in ammonium uptake may be due to the decline in hydrogen (H⁺) ion concentration in exposed plants which resulted from the reduction of the nitrate and nitrite from NO₂ absorption. They also suggest that the decrease in ammonium uptake and the competition for energy between nitrate reduction and ammonium assimilation may limit ammonium assimilation to organic nitrogen (N) which would further inhibit acidity increase in exposed plants and ammonium uptake by roots.     

Intraspecific differences in nitrogen assimilating enzymes in spinach under contrasting forms of nitrogen supply 1

Intraspecific differences in the activities of nitrate reductase (NR), glutamine synthetase (GS), NADH dependent glutamate synthase (NADH‐GOGAT), and glutamate dehydrogenase (GDH) under contrasting forms of nitrogen (N) supply were studied in tissues of three spinach (Spinacia oleracea L.) cultivars. The varieties (Viroflay, Butterflay, and Giant) were smooth, curly and semicurly leaved, respectively. The plants were grown in nutrient solutions containing NO₃ as the sole source of N (100:0) and NO₃ plus NH₄ (80:20). Giant, the NH₄ tolerance of which had been evaluated in growth and on the basis of nutrient uptake, had much higher GS and GDH activities in the roots and higher NR and NADH‐GOGAT levels in the leaves of plants grown on NO₃ and NH₄ than that grown on NO₃ alone. On the level of N assimilating enzymes of Butterflay, mixed N nutrition caused an increase of GDH and NADH‐GOGAT in leaves and roots and at the same time a decrease of GS in the roots and NR in the leaves. An inverse relationship between GS and GDH activities was detected in the leaves and foots of Virofiay grown with both N sources. Finally, Viroflay gave the highest levels of GDH irrespective of the NO₃:NH₄ assayed, whereas the leaves of Giant were GDH deficient in comparison with the other cultivars. In addition, the GS activity approached zero in the roots of spinach cultivars characterized by hardly any NH₄ tolerance, whereas in those of Giant it increased remarkably with the supply of NO₃ plus NH₄.     

Alterations in the mineral nutrition of pea seedlings exposed to cadmium 1

A study was made of the effects of different levels of cadmium (Cd) in the nutrient solution (0.0, 1.5, and 6.0 mg/L Cd) on the assimilation of nitrate (NO₃ ^‐) and the uptake and distribution of cationic nutrients in pea (Pisum sativum cv. Argona) seedlings. Cadmium treatment resulted in an accumulation of NO₃ ^‐ in the root, indicating an alteration in NO₃ ^‐ translocation to the shoot. This was related to a decrease in the nitrate reductase (NR) activity in the shoot, severely inhibiting NO₃ ^‐ assimilation, and associated to a reduction in fresh tissue weight and in their relative water content. The concentration of potassium (K) decreased in both root and shoot, but its relative distribution between those tissues was not affected by the presence of Cd. Among other cationic nutrients, manganese (Mn) was the most affected, its concentration constantly decreased concomitantly with the increase in Cd supply. The distribution of Mn between shoot and root revealed that more was accumulated in the shoot than in the root, opposite to the distribution of NO₃ ^‐ The ‘shock’ addition of 6.0 mg/L Cd in a short‐term experiment confirmed that the transport of NO₃ ^‐ to the aerial part was reduced after 72 h of treatment and Cd displaced Mn from its physiological positions in root tissues.     

Effects of Forms and Rates of Zinc Fertilizers on Cadmium Concentrations in Two Cultivars of Maize

Abstract

A pot experiment was conducted to investigate the effects of three soluble zinc (Zn) fertilizers on cadmium (Cd) concentrations in two genotypes of maize (Zea mays): Jidan 209 and Changdan 374. Zinc fertilizers were added to soil at four levels: 0, 80, 160, and 240 mg kg^?1 soil as nitrate [Zn(NO₃)₂], chloride (ZnCl₂), and sulfate (ZnSO₄). Cadmium nitrate [Cd(NO₃)₂] was added to all the treatments at a uniform rate equivalent to 10 mg kg^?1 soil. The biomass of maize plants was increased with the application of three zinc fertilizers, of which Zn(NO₃)₂ yielded more than others. Under ZnCl₂ treatment, plant growth was promoted at the lower level and depressed at the higher one. All the three fertilizers decreased Cd concentration in shoots in comparison with treatments without Zn, but there were variations with different forms, especially in plants treated with Zn(NO₃)₂, which had the minimal value. The orders of average Cd concentration in shoots with different zinc fertilizers were ZnSO₄>ZnCl₂>Zn(NO₃)₂ for Jidan 209 and ZnCl₂>ZnSO₄>Zn(NO₃)₂ for Changdan 374, respectively (P<0.001). There was no significant difference between ZnSO₄ and ZnCl₂ treatments. The lowest Cd concentration in shoots was found in the 80‐mg‐kg^?1 soil or 160‐mg‐kg^?1 soil treatment. Cadmium concentration in roots in the presence of ZnCl₂ was the lowest and under ZnSO₄ the highest. The mechanism involved needs to be studied to elucidate the characteristics of complexation of Cl^? and SO₄ ^2? with Cd in plants and their influence on transfer from roots to shoots.     

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.     

Cadmium accumulation and distribution in sunflower plant

Cadmium (Cd) accumulation and distribution was studied in sunflower (Helianthus annuus L., public line HA‐89) plant. From an uncontaminated sandy loam brown forest soil with 162 μg kg^‐1 HNO₃/H₂O₂ extractable Cd the HA‐89 sunflower public line accumulated 114 ug kg^‐1 Cd in its kernels under open field conditions. This value is rather low as compared to data found by others. Sandy loam brown forest soil was treated with 0, 1 or 10 mg kg^‐1 of Cd to study the interaction of this heavy metal with young sunflower plants in a greenhouse pot experiment. The fresh weight and dry matter accumulation of sunflower plant organs (roots, shoots, leaves or heads) was unaffected by cadmium treatment of soil. The nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), or zinc (Zn) uptake of sunflower plant organs was not influenced by lower or higher Cd‐doses, except sunflower heads where 10 mg kg^‐1 of Cd treatment of soil significantly reduced the uptake of Ca, Fe, and Mn. Although Cd reduced the Zn uptake of roots, its rate was statistically not significant. Cadmium was accumulated prevalently in roots (1.21 mg kg^‐1,4.97 mg kg^‐1, or 13.69 mg kg^‐1 depending on Cd‐dose), and its concentration increased also in shoots or leaves. In spite of the short interaction time, elevated concentrations of cadmium (0.78 mg kg^‐1, 1.34 mg kg^‐1, or 3.02 mg kg^‐1 depending on Cd‐dose) were detected in just emerged generative organs (heads) of young sunflower plants.     

The influence of the form of nitrogen nutrition on uptake and distribution of cadmium in lettuce varieties

Four lettuce (Lactuca saliva L.) varieties ('Benita’, ‘Wendy’, ‘Mirena’, and ‘Jacky') were grown for 43 days in a pH‐controlled complete nutrient solution without cadmium (Cd) or with either 0.01 or 0.03 mg Cd/1 and with NH₄ or NO₃ as the form of nitrogen nutrition. Cadmium did not affect dry matter yield. ‘Wendy’ had a significantly higher total dry matter production when grown on NO₃ compared to NH₄, whereas growth of ‘Mirena’ was best on NH₄ (P<0.05). Dry weights of ‘Benita’ and ‘Jacky’ were not affected by the N source. Cadmium concentrations in shoots (and roots) of plants grown on NH₄ were significantly higher than in plants grown on NO₃. The Zn concentrations in the shoots were also enhanced. The distribution of Cd in the lettuce varieties was independent of the form of N nutrition. It is concluded that the N source directly affects the amount of Cd taken up, without influencing the Cd distribution.     

Effect of split applications of nitrogen fertilizer on the growth and nitrogen composition of Chinese mustard

Abstract

We assessed the effect of split applications of nitrogen (N) fertilizer on the growth and N composition of Chinese mustard. There were six treatments in which various rates of N fertilizer were applied as a basal dressing and two top dressings. The plants were harvested 40 days after seeding and the N composition of the plants determined. The soil was also sampled and the pH, electrical conductivity (EC) of 1:1 soil:water ratio extract, organic matter, nitrate‐nitrogen (NO₃‐N), Bray Pl‐extractable phosphorus (P) as well as 1N neutral ammonium acetate‐extractable potassium (K), calcium (Ca), and magnesium (Mg) concentrations after harvesting of the plants determined. The results show that there was no significant difference in yield from the various treatments. Total N concentration in shoots receiving the 1–2–1 fertilizer treatment was higher than that of the other treatments. However, NO₃‐N, soluble reduced N, and insoluble N concentrations in shoots as well as NO₃‐N, soluble reduced N, insoluble N, and total N concentrations of roots were not significantly different due to the treatments.     

Ionic balance,biomass production,and organic nitrogen as affected by salinity and nitrogen source in annual ryegrass

Studies on the effects of salinity and nitrogen (N) fertilization on ionic balance, biomass, and organic N production of annual ryegrass (Lolium multiflorum Lam.) were conducted. Plants grown in sand were irrigated with nutrient solution with an electrical conductivity of 2 or 11.2 dS#lbm^‐1, and N in the form of sodium nitrate (NaNO₃), ammonium nitrate (NH₄NO₃), or ammonium sulfate [(NH₄)₂SO₄] ranging from 0.5 to 9.0 mM. Salinity increased the concentration of total inorganic cations (C) in plants and specifically sodium (Na) by more than 3‐fold higher in plants grown at high salinity as compared with plants at low salinity. Sodium (Na) concentration in roots was higher than in shoots irrespective of the salinity level, suggesting a restriction of Na transport from roots to shoots. The concentration of total inorganic anions (A) increased with salinity and when plants were supplied with nitrate (NO₃), salinity increased the concentrations of NO₃ and chloride (Cl) in plants. Increasing salinity and N concentration in the growth medium increased organic anions concentration in plants, estimated as the difference between C and A. The effect of different N sources on C‐A followed the order: NH₄NO₃ > NO₃ > ammonium (NH₄). The base of organic anions and inorganic ions with salinity contributed significantly to the osmotic potential of plants shoots and roots. Changes in C affected N and organic acids metabolism in plants, since C were highly correlated (p=0.0001) with C‐A and organic N (N_org) concentrations regardless of the salinity level or N source in the nutrient solutions. A high and positive linear dependency was found between N_org and C‐A in plants grown at high and low salinity levels and different N sources, pointing out the close relationship between N_org and organic anions on metabolism under these conditions. The amount of biomass produced was correlated positively with organic anion concentration in plants exposed to different salinity levels. Plant biomass increased with N concentration in the nutrient solution regardless of the salinity level applied. Biomass accumulation decreased while N_org concentration increased with salinity. Organic N content remained unaffected in plants exposed to salinity when grown in N less than 9.0 mM.     

The significance of plant energy status for the uptake and incorporation of NH4-nitrogen by young rice plants

Uptake and assimilation of inorganic N in young rice plants has been studied with labelled N (N-15). Depletion of the plants' carbohydrate content, obtained by a preceding dark period, resulted in a drastic reduction of NH₄ ⁺-N uptake. Plants exposed to low light intensity showed diminishing NH₄ ⁺-N uptake rates as compared with plants exposed to full light intensity, the latter showing constant NH₄ ⁺-N uptake rates during the whole experimental period. The percentage of labelled insoluble N in total labelled N was not significantly affected by a preceding dark period, whereas the low light intensity resulted in a lower proportion of insoluble N in roots and shoots. The incorporation of labelled N into the insoluble fraction (proteins, nucleic acids) was higher in plants fed with NH₄ ⁺-N than in those fed with NO₃ ^-.

The uptake of NH₄ ⁺-N was not significantly affected by NO₃ ^-, whereas the NO₃- uptake rate was considerably reduced in the presence of NH^{4 +}-N. Low energy status of plants affected the nitrate uptake more than the uptake of NH₄ ⁺-N. The results show that uptake and assimilation of inorganic N depend much on the energetic status of plants. Nitrate uptake and assimilation is more sensitive to low energy conditions than NH₄ ⁺-N.     

Effects of Soil Amended with Cadmium and Lead on Growth,Yield, and Metal Accumulation and Distribution in Parsley

A greenhouse experiment was designed to determine the cadmium (Cd) and lead (Pb) distribution and accumulation in parsley plants grown on soil amended with Cd and Pb. The soil was amended with 0, 5, 10 20, 40, 60, 80, and 100 mg Cd kg^?1 in the form of cadmium nitrate [Cd(NO₃)₂] and 0, 5, 10, 50 and 100 mg Pb kg^?1 in the form of lead nitrate [Pb(NO₃)₂]. The main soil properties; concentrations of the diethylenetriaminepentaacetic acid (DTPA)–extractable metals lead (Pb), Cd, copper (Cu), iron (Fe), zinc (Zn), and manganese (Mn) in soil; plant growth; and total contents of metals in shoots and roots were measured. The DTPA-extractable Cd was increased significantly by the addition of Cd. Despite the fact that Pb was not applied, its availability was significantly greater in treatments 40–100 mg Cd kg^?1 compared with the control. Fresh biomass was increased significantly in treatments of 5 and 10 mg Cd kg^?1 as compared to the control. Further addition of Cd reduced fresh weight but not significantly, although Cd concentration in shoots reached 26.5 mg kg^?1. Although Pb was not applied with Cd, its concentration in parsley increased significantly in treatments with 60, 80, and 100 mg Cd g^?1 compared with the others. Available soil Pb was increased significantly with Pb levels; nevertheless, the increase was small compared to the additions of Pb to soil. There were no significant differences in shoot and root fresh weights between treatments, although metal contents reached 20.0 mg Pb kg^?1 and 16.4 mg Pb kg^?1 respectively. Lead accumulation was enhanced by Pb treatments, but the positive effect on its uptake was not relative to the increase of Pb rates. Cadmium was not applied, and yet considerable uptake of Cd by control plants was evident. The interactive effects of Pb and Cd on their availability in soil and plants and their relation to other metals are also discussed.     

Effect of Amino Acid Fertilization on Nitrate Assimilation of Leafy Radish and Soil Chemical Properties in High Nitrate Soil

Abstract

The objective of the present work was to investigate the corresponding uptake and assimilation of nitrate (NO₃ ^?) in leafy radish and effects on soil chemical properties by foliar application of amino acid fertilizer (AAF). The activity of the enzymes related to the process of NO₃ ^? reduction (NR: nitrate reductase; NiR: nitrite reductase; GS: glutamine synthetase) and the content of NO₃ ^?, total N, and the end products of this process (amino acids and proteins) were analyzed. The soils were sampled twice, and some chemical properties were analyzed. The results of this study showed that application of AAF increased biomass production, and nitrogen (N) utilization in the treatment of a low rate of AAF increased 55% over the control. In addition, the activities of the enzymes were affected differently depending on applied rate of AAF. Furthermore, the NO₃ ^? content was reduced 4–24%, and total N content was increased 14–32% by AAF treatments. Finally, application of AAF improved uptake efficiency of N from soil and prevented N loss by leaching.     

Nitrate versus chloride nutrition effects in a soil‐plant system on the growth,nitrate accumulation,and nitrogen,potassium, sodium,calcium, and chloride content of carrot

The experiment was conducted to evaluate the effects of various nitrate/ chloride (NO₃/Cl) ratios on growth, nitrate accumulation, and mineral absorption in carrot, Daucus carota L., plants in a controlled environment. The experiment included two Cl sources [potassium chloride (KC1) and calcium chloride (CaCl₂)] and five NO/Clratios at 100/0, 90/10, 80/20, 70/30, and 60/40 with total‐nitrogen (N) concentration of 400 mg NO₃ kg^‐1 soil in 100/0 treatment. Fresh and dry weights of shoots and storage roots, and length and diameter of storage roots increased significantly with mixed NO₃/C1 treatments with both Cl sources as compared to single NO₃ (100/0) treatment. Growth was enhanced up to the 80/20 NO₃/C1 treatments. With Cl present in the treatments, the concentration of total‐N unchanged and NO₃ decreased in plants, and Cl and potassium (K) increased with the Cl sources. In KC1 treatments, Na absorption decreased. Calcium (Ca) content of the plants significantly differed by the treatments. It was concluded that N fertilization provided with combined Cl forms and NO₃/Cl rates can enhance production of better quality carrot and at the same time decrease of the N fertilizer input.     

Cadmium and Nutrient Heavy Metals Uptake by Rice,Barley, and Spinach as Affected by Four Ammonium Salts

This experiment was conducted to investigate the influence of ammonium salts on the uptake of cadmium (Cd) and nutritional heavy metals (copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe)) by rice, barley, and spinach. These plants were grown in Cd, Cu, and Zn contaminated entisol (ES) or andisol (AS). The following ammonium salts were used: ammonium nitrate (NH₄NO₃), ammonium sulfate ((NH₄)₂SO₄), ammonium chloride (NH₄Cl), and ammonium dihydrogen phosphate (NH₄H₂PO₄). In ES, the Cd concentrations in three plant shoots were higher with NH₄Cl than with the other salts. The concentrations of Cd in soil solutions collected from ES were higher with NH₄Cl. Thus, the increase of Cd uptake by three plants with NH₄Cl treatment would be caused by the increased concentration of Cd in the soil solution. In contrast, in AS, the concentrations of the heavy metals in the shoots of all plants were not different among NH₄ applications, with one exception, the Mn concentration in rice increased with NH₄Cl in both ES and AS.     

Tomato growth,nitrogen fraction and mineral composition in response to nitrate and ammonium foliar sprays 1

Tomato plants were grown in sand culture with NO₃ or NH₄ N at two levels of light. Foliar sprays at three levels of N as well as combinations of foliar and root feeding were used.

Shade increased NH₄ toxicity in plants sprayed with NH₄ but decreased the toxicity in plants receiving NH₄ through the roots. NH₄‐N greatly reduced growth and cation uptake when supplied through the roots but not with foliar application. Plants sprayed with NH₄ showed better growth, higher K, Ca, and Mg content and lower free NH₄ in shoot, compared to plants receiving NH₄ through the roots.

The overall free amino acid contents of shoots was higher for NH₄‐fed plants regardless of how the N was applied. Plants sprayed with NH₄ incorporated a greater amount of N into insoluble compounds compared with NO₃ nutrition. The N uptake per unit of leaf area was higher for plants grown under full sun light whereas N content was higher for plants grown under hade. N content in tissue increased with N concentration in foliar spray, although plants supplied with N through the roots had higher levels of free amino acids and total nitrogen.     

Phytotoxicity of Cadmium in Radish and Its Effects on Growth,Yield, and Cadmium Uptake

A greenhouse experiment was conducted to study the effects of cadmium (Cd) on growth, biomass yield, and Cd uptake in three radish (Raphanus sativus L.) varieties at the Indian Institute of Horticultural Research, Bangalore, India, during 2008–2009. Plants were subjected to different Cd levels by application of cadmium nitrate [Cd (NO₃)₂] at the rates of 0, 50, 100, and 200 mg Cd kg^?1 soil. Length and fresh and dry biomass yields of shoots and roots decreased because of the phytotoxic effect of Cd. Among three varieties, Japanese White Long showed the greatest sensitivity to Cd toxicity. The accumulation of Cd in shoots and roots was greatest in Japanese White Long, which had greater bioconcentration factor values. Variety Arka Nishanth recorded lower bioconcentration factor values and greater transfer coefficient values, indicating lower Cd accumulation in root tubers in this variety. Hence, variety Arka Nishanth can be preferred in Cd-contaminated soils.