Selecting iodine-enriched vegetables and the residual effect of iodate application to soil

A greenhouse pot experiment was conducted to select vegetables for iodine uptake. The residual effect of iodate fertilization on the growth of and iodine uptake by spinach plants were also investigated. Six vegetables, including leafy vegetables (pakchoi [Brassica chinensis L.], spinach [Spinacia oleracea L.]), tuber vegetables (onion [Allium cepa L.]), shoot vegetables (water spinach [Ipomoea aquatica Forsk.], celery [Apium graveolens L.]), and root vegetables (carrot [Daucus carota var. sativa DC.]) were examined. Results showed that the concentrations of iodate in soil had significant effect on the biomass of edible parts of pakchoi and spinach (p<0.01), whereas the concentrations of iodate in soil had no significant effect on that of carrots, water spinach, celery, and onion. Iodine concentrations in edible parts of vegetables and the transfer factors (TF_{edible parts}) of soil-to-edible parts of vegetables significantly increased with increasing iodine concentrations in soil (p<0.001), and iodine concentrations in edible parts and TF_{edible parts} of spinach were much higher than those of other vegetables at any treatment. Both transfer coefficients for edible parts (TC_{edible parts}) and for aerial parts (TC_{aerial parts}) of vegetables changed differently with increasing iodine concentrations in the soil, and TC_{edible parts} and TC_{aerial parts} of spinach were higher than those of other vegetables. Therefore, spinach (leafy vegetable) was considered as an efficient vegetable for iodine biofortification. Further experiment showed that there is considerable residual effect of soil fertilization with iodate.     

Evaluation of Iodide and Iodate for Adsorption–Desorption Characteristics and Bioavailability in Three Types of Soil

Adsorption–desorption of iodine in two forms, viz., iodide (I⁻) and iodate (IO₃⁻), in three types of soil were investigated. The soils were: red soil developed on Quaternary red earths (REQ)— clayey, kaolintic thermic plinthite Aquult, Inceptisol soil (IS) and alluvial soil (AS)—Fluvio-marine yellow loamy soil. The isothermal curves of iodine adsorption on soils were described by Langmuir and Freundlich equation, and the maximum adsorption values (y _m) were obtained from the simple Langmuir model. As compared with the iodide, the iodate was adsorbed in higher amounts by the soils tested. Among three soils, the REQ soil adsorbed more iodine (I⁻ and IO₃⁻) than the IS and AS. The distribution coefficient (K _d) of iodine in the soils decreased exponentially with increasing iodine loading concentration. Desorption of iodine in soil was increased correspondingly with increasing adsorption values. The REQ soil had a greater affinity for iodine than the IS and AS at the same iodine loadings. In the pot experiment cultivated with pakchoi (Brassica chinensis L.) and added with two exogenous iodine sources, the iodide form was quickly taken up by pakchoi and caused more toxicity to the vegetable. The rate of iodine loss from soil was higher for iodide form as compared with the iodate. The iodine bioavailability was the highest but the persistence was the weakest in AS among the three soils tested, and the REQ soil showed just the opposite trend to that of the AS soil. This study is of theoretical importance to understand the relationship between iodine adsorption–desorption characteristics and their bioavailability in different soils and it also has practical implications for seeking effective alternatives of iodine biofortification to prevent iodine deficiency disorders.     

Photosynthesis and metabolism of sugars from lettuce plants (<Emphasis Type="Italic">Lactuca sativa</Emphasis> L. var. longifolia) subjected to biofortification with iodine

Iodine, essential to human life, is in part ingested through vegetable consumption, explaining the current application of this element in biofortification programs. Few data are available on the effects of iodine on main plant metabolisms such as carbon metabolism. The objective of this study was to determine the effect of the application of different doses (20, 40 and 80 μM) and forms of iodine (iodate [IO₃ ⁻] and iodide [I⁻]) on photosynthesis and carbohydrate metabolism in lettuce plants. None of these treatments exerted significant effects on the synthesis pathway or on sucrose degradation. Application of 80 μM of I⁻ reduced the photosynthesis rate, which may be associated with the reduction found in biomass and photosynthetic parameters (stomatic conductance and transpiration). This finding confirms that the application of high doses of I⁻ has a phytotoxic effect on plant physiology. In contrast, all IO₃ ⁻ treatments increased the biomass of the plants which showed an elevated photosynthetic rate, stomatic conductance, and transpiration (vs. controls). The differential crop behavior observed with the two forms of this trace element suggests that IO₃ ⁻ should be selected for future biofortification programs.     

Does Iodine Biofortification Affect Oxidative Metabolism in Lettuce Plants?

Plants produce low levels of reactive oxygen species (ROS), which form part of basic cell chemical communication; however, different types of stress can lead to an overexpression of ROS that can damage macromolecules essential for plant growth and development. Iodine is vital to human health, and iodine biofortification programs help improve the human intake through plant consumption. This biofortification process has been shown to influence the antioxidant capacity of lettuce plants, suggesting that the oxidative metabolism of the plant may be affected. The results of this study demonstrate that the response to oxidative stress is variable and depends on the form of iodine applied. Application of iodide (I⁻) to lettuce plants produces a reduction in superoxide dismutase (SOD) activity and an increase in catalase (CAT) and L-galactono dehydrogenase enzyme activities and in the activity of antioxidant compounds such as ascorbate (AA) and glutathione. This did not prove a very effective approach since a dose of 80 μM produced a reduction in the biomass of the plants. For its part, application of iodate (IO₃⁻) produced an increase in the activities of SOD, ascorbate peroxidase, and CAT, the main enzymes involved in ROS detoxification; it also increased the concentration of AA and the regenerative activities of the Halliwell–Asada cycle. These data confirm the non-phytotoxicity of IO₃⁻ since there is no lipid peroxidation or biomass reduction. According to our results, the ability of IO₃⁻ to induce the antioxidant system indicates that application of this form of iodine may be an effective strategy to improve the response of plants to different types of stress.     

Photorespiration Process and Nitrogen Metabolism in Lettuce Plants (Lactuca sativa L.): Induced Changes in Response to Iodine Biofortification

Iodine is vital to human health, and iodine biofortification programs help improve human intake through plant consumption. There is no research on whether iodine biofortification influences basic plant physiological processes. Because nitrogen (N) uptake, utilization, and accumulation are determining factors in crop yield, the aim of this work was to establish the effect of the application of different doses (20, 40, and 80 μM) and forms of iodine (iodate [IO₃ ⁻] vs. Iodide [I⁻]) on N metabolism and photorespiration. For this study we analyzed shoot biomass and the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), aspartate aminotransferase (AAT), glutamate dehydrogenase (GDH), glycolate oxidase (GO), glutamate:glyoxylate aminotransferase (GGAT), serine:glyoxylate aminotransferase (SGAT), hydroxypyruvate reductase (HR) and catalase (CAT), nitrate (NO₃ ⁻), ammonium (NH₄ ⁺), organic and total N, amino acids, proteins, serine (ser), malate, and α-ketoglutaric acid in edible lettuce leaves. Application of I⁻ at doses of at least 40 μM reduced the foliar concentration of NO₃ ⁻ with no decrease in biomass production, which may improve the nutritional quality of lettuce plants. In contrast, the application of 80 μM of I⁻ is phytotoxic for lettuce plants, reducing the biomass, foliar concentration of organic N and NO₃ ⁻, and NR and GDH activities. HR activity is significantly inhibited with all doses of I⁻; the least inhibition was at 80 μM. This may involve a decrease in the incorporation of carbonated skeletons from photorespiration into the Calvin cycle, which may be partially associated with the biomass decrease. Finally, the application of IO₃ ⁻ increases biomass production, stimulates NO₃ ⁻ reduction and NH₄ ⁺ incorporation (GS/GOGAT), and optimizes the photorespiratory process. Hence, this appears to be the most appropriate form of iodine from an agronomic standpoint.     

Reduction of iodate in iodated salt to iodide during cooking with iodine as measured by an improved HPLC/ICP–MS method

Background: Iodate is a strong oxidant, and some animal studies indicate that iodate intake may cause adverse effects. A key focus of the safety assessment of potassium iodate as a salt additive is determining whether iodate is safely reduced to iodide in food. Objective: To study the reduction of iodate in table salt to iodide and molecular iodine during cooking. Materials and Methods: Fifteen food samples cooked with and without iodated salt were prepared in duplicate. The iodine in the cooked food was extracted with deionized water. The iodine species in the extracts were determined by using an improved high-performance liquid chromatography/inductively coupled plasma–mass spectrometry (HPLC/ICP–MS). The cooking temperature and the pH of the food were determined. Results: The conversion rate of iodate in iodated salt to iodide and molecular iodine was 96.4%±14.7% during cooking, with 86.8%±14.5% of the iodate converted to iodide ions and 9.6% ±6.2% converted to molecular iodine to lose. The limit of detection, limit of quantification, relative standard deviation and recovery rate of the method HPLC/ICP–MS were 0.70 μg/L for I⁻ (0.69 μg/L for IO₃⁻), 2.10 μg/L for I⁻ (2.06 μg/L for IO₃⁻), 2.6% and 101.6%±2.6%, respectively. Conclusion: Almost all iodate added to food was converted into iodide and molecular iodine during cooking. The improved HPLC/ICP–MS was reliable in the determination of iodine species in food extracts.     

Nitrate reductase activity of two leafy vegetables as affected by nickel and different nitrogen forms

The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO₃ ⁻–N, NH₄ ⁺–N, NH₄NO₃). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in lettuce plants supplied with nitrate nitrogen (NO₃ ⁻–N) or mixed (NH₄NO₃) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants. At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with NO₃ ⁻–N or NH₄NO₃. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the enzyme activity in the roots of NO₃ ⁻-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution contained ammonium nitrogen (NH₄ ⁺–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs, especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated with NH₄ ⁺–N the enzyme activity in roots was even higher than in those supplied with NO₃ ⁻–N.     

Different tissue responses for iodine and iodide in rat thyroid and mammary glands

This research describes the effects of short-term elemental iodine (I₂) and iodide (I⁻) replacement on thyroid glands and mammary glands of iodine-deficient (ID) Sprague-Dawley female rats. Iodine deficiency causes atypical tissue and physiologic changes in both glands. Tissue histopathology and the endocrine metabolic parameters, such as serum TT₄, tissue and body weights, and vaginal smears, are compared. A moderate reduction in thyroid size from the ID control (IDC) was noted with both I⁻ and I₂, whereas serum total thyroxine approached the normal control with both I⁻ and I₂, but was lower in IDC. Thyroid gland IDC hyperplasia was reduced modestly with I₂, but eliminated with I⁻. Lobular hyperplasia of the mammary glands decreased with I₂ and increased with I⁻ when compared with the IDC; extraductal secretions remained the same as IDC with I₂, but increased with I⁻; and periductal fibrosis was markedly reduced with I₂, but remained severe with I⁻. Thus, orally administered I₂ or I⁻ in trace doses with similar iodine availability caused different histopathological and endocrine patterns in thyroid and mammary glands of ID rats. The significance of this is that replacement therapy with various forms of iodine are tissue-specific.     

Iodine toxicity in a plant-solution system with and without humic acid

Aqueous iodine (I_2(aq)) is a potent disinfectant that is being evaluated as a soil sanitizer for agricultural fields and a water purification treatment for the International Space Station. Rice (Oryza sativa L.) plants were grown in solution culture containing different I compounds at approximately 0, 18, or 30 μM total I [I_2(aq) + iodide (I⁻)] consisting of 0, 6, and 20 μM I as I_2(aq), respectively. In addition, humic acid (HA) was added to half the treatments. Most I_2(aq) was electrochemically reduced to the endpoint metabolite I⁻ within 24 h with HA promoting the response. Plants receiving the highest dose of I_2(aq), particularly those in treatments without HA, had the least growth and the greatest biomass I concentrations. Roots from both I_2(aq) treatments without HA were periodically sampled for bacteria. Viable and direct caints of bacterial cell density declined with increasing I_2(aq) concentrations within the first hour after treatment application. However, cell densities recovered within 96 hours and eventually surpassed the control treatment cell density. Additionally, the resulting high viable: direct count density ratio suggests that opportunistic species likely dominated the post I_2(aq) environment.     

Buckwheat accumulates aluminum in leaves but not in seeds

Buckwheat (Fagopyrum esculentum Moench. cv Jianxi) is highly resistant to Al stress and is known to be an Al-accumulator. Pot experiments were carried out in a greenhouse to investigate the accumulation of Al in leaves and seeds of buckwheat. Plants were grown for 12 weeks in a strong acid soil amended with or without CaCO₃ at a rate of 1 g kg⁻¹ soil. Old leaves accumulated as much as 10 g kg⁻¹ Al of dry weight when the plants were grown in the acid soil, while the Al concentrations in leaves immediately adjacent to seeds, seed coats, and embryos were, on average, 4516, 41.2 and 7.7 mg kg⁻¹, respectively. The Al concentration significantly decreased in leaves when the plants were grown in the limed soil, and the Al concentrations in leaves immediately adjacent to seeds, seed coats, and embryos were, on average, 1586, 21.3 and 3.1 mg kg⁻¹, respectively. These results show that seeds accumulate much less Al than buckwheat leaves. The underlying mechanisms are discussed. Section Editor: H. Lambers     

An environmental approach to correcting iodine deficiency: Supplementing iodine in soil by iodination of irrigation water in remote areas

OBJECTIVE: Iodine deficiency disorders continue to be a severe problem in many parts of Central Asia, causing delayed mental development and cretinism in indigenous populations. In some areas, iodized salt has not succeeded in controlling this problem. In southern Xinjiang Province of China, we tried a new method of supplying iodine to rural populations by dripping potassium iodate into irrigation water canals. By this means iodine was distributed into soil, crops, animals and people. This proved feasible and cost effective; it reached all the people, required no medical expertise, required no continuing effort after the initial dripping, and had the important added benefit of improving livestock production. METHODS: We serially monitored iodine concentrations in soil, crops, animal products and human urine for several years after the last dripping. In a similar project in Inner Mongolia, total soil iodine was determined in addition. Here, iodine concentrations in soil, crops, animals and people have been monitored for 4 years after supplementation. RESULTS: After dripping, total iodine increased two-fold, while soluble iodine increased 4-5-fold. Iodine added to soil is available for more than 4 years after a single application. CONCLUSIONS: Potassium iodate added to soil appears to increase soluble iodine out of proportion to the amount added. This effect and the long persistence of dripped iodate in soil contribute to the efficacy and cost effectiveness of this method of iodine supplementation.     

蔬菜吸收不同形态外源碘的动力学特性

采用水培法,研究了两种蔬菜(小白菜和芹菜)对两种不同形态碘源(I-,IO-3)的吸收和积累特性.结果表明:供试蔬菜吸收碘的速率表现为在短时间(＜60 min)内迅速增加,随着时间的延长蔬菜对碘的吸收速率逐渐下降;在低浓度范围内(0.01～0.50 mg/L)蔬菜对IO-3的吸收速率与碘浓度变化曲线符合饱和吸收动力学特征(表现为遵循酶学方程),进一步研究表明,解偶联剂2,4-二硝基苯酚(DNP)对低浓度(＜0.50 mg/L)下蔬菜IO-3吸收速率具有明显的抑制作用,说明两种蔬菜对低浓度的IO-3可能存在主动吸收,而在高浓度范围内(0.50～10.0 mg/L),蔬菜对碘的吸收速率随着碘浓度的提高呈现直线上升的趋势.两种蔬菜相比,在同样条件下芹菜对碘的吸收速率明显大于小白菜.蔬菜可食部分中碘的含量随着碘浓度的提高而增加,在一次加碘条件下表现为先增加后降低的趋势,而在持续加碘条件下蔬菜中碘的含量在整个处理期间表现为不断增加; Cl-的添加对低浓度下蔬菜碘的吸收具有明显的抑制作用,而随着碘浓度的提高Cl-的抑制作用逐渐减弱.供试蔬菜对碘的富集系数随碘浓度的提高而降低,碘在蔬菜不同器官的分配次序表现为根＞叶＞茎.     

Bicarbonate,the most important factor inducing iron chlorosis in vine grapes on calcareous soil

Summary In pot experiments grape vine was grown on a calcareous and on a non calcareous soil with a low and with a high water saturation. During the growing period soil solution samples were collected and analyzed for their pH and for HCO ₃ ⁻ , phosphate, Fe, and Ca. High water saturation resulted in a pH increase and in an increase of the HCO ₃ ⁻ concentration in both soils. The level in pH and HCO ₃ ⁻ , however, was much higher in the calcareous soil than in the non calcareous soil. The Fe concentration varied much throughout the experimental period, but there was no major differences between soils and water saturation treatments. The Ca concentration of the soil solution increased with time in the calcareous soil; for the non calcareous soil rather the reverse was true. The phosphate level in the soil solution of the non calcareous soil was about 10 times higher than in the calcareous soil. After 3 weeks growth all plants of the calcareous soil with the high water saturation showed first symptoms of Fe deficiency. These became more intense from day to day. Plants of the other treatments did not show any chlorotic symptoms. In the treatment with the chlorotic plants the HCO ₃ ⁻ concentration of the soil solution was the highest, the phosphate concentration the lowest from all treatments. It is therefore concluded that HCO ₃ ⁻ and not phosphate is the primary cause for lime induced Fe chlorosis. Despite the low phosphate concentration in the soil solution, the P concentration in the chlorotic leaves was more than twice as high as the P concentration in green leaves grown on the same soil. It is thus assumed that the high P content frequently found in chlorotic leaves is the result and not the cause for Fe chlorosis.     

Alleviation of nickel toxicity by ammonium supply to sunflower plants

Phytotoxicity of nickel (Ni) varies within plant species and cultivars as well as with the concentration of Ni in the rooting medium. Moreover, it is known that several nutrients can modify the plant response to excess Ni. Nitrogen can be absorbed by plants as different N forms and because N metabolism and Ni are closely related, a hydroponic experiment was conducted to study the effect of Ni toxicity on the growth, nutrient status of the different plant parts and leaf chlorophyll concentrations in sunflower plants (Helianthus annuus L.) cv Quipu grown with different forms of N supply. The plants were grown under controlled conditions for 35 days. Depending on the N source supplied, there were significant differences in the sensitivity of sunflower plants to excess Ni. Tolerance was lowest when grown with NO₃ ⁻ alone. A high Ni and NO₃ ⁻ as the only N source resulted in reduced dry weight and significant decreases in nutrient concentration. Plants supplied with a mixture of NO₃ ⁻ and NH₄ ⁺ absorbed in the presence of Ni in solution about three times less Ni than those supplied with NO₃ ⁻ alone. Consequently, there were great differences in Ni concentrations between treatments. With a N nutrition of 100% NO₃ ⁻-N, Ni supply led to severe growth inhibition. Just contrary, simultaneous supply of NO₃ ⁻ and NH₄ ⁺ not only reduced Ni toxicity, but growth was even stimulated by Ni if supplied to plants fed with NO₃ ⁻ and NH₄ ⁺. This indicates the significant role of the N form supplied in the behaviour of Ni toxicity in sunflower plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Osmotic adjustment inSorghum bicolor (L. Moench) grown under moisture stress in soil and osmotically modified solution cultures

Sorghum (Sorghum bicolor L. Moench) plants were grown in solution culture and stressed at three rates of decreasing leaf water potential (−0.123, −0.068 and −0.029 MPa day⁻¹) achieved by the incremental addition of an osmoticum, polyethylene glycol (PEG) 6000 to the solutions. Plants were also grown in soil and given different amounts of water which resulted in rates of decreasing leaf water potentials of −0.130 and −0.073 MPa day⁻¹. The rate of stress and the culture system influenced the accumulation of solutes in the cell, but not cell volume. A rapid stress (−0.123 and −0.130 MPa day⁻¹) to approximately −1.6 MPa leaf water potential resulted in 0.75 and 0.16 MPa of osmotic adjustment in the PEG and soil culture respectively. At moderate stress (−0.068 and −0.073 MPa day⁻¹) respective values were 1.68 and 0.58 MPa. There were some visual symptoms in the solution grown plants characteristic of uptake of high molecular weight PEG. However the relative growth rates of these plants were equal to or greater than those of the soil grown plants. In view of the differences in plant water status of soil and PEG solution cultured plants it was concluded that the use of the latter system would not be entirely suitable for some studies of drought resistance in sorghum, as related to crop performance in the field.     

Radiotracer Experiments on Biological Volatilization of Organic Iodine from Coastal Seawaters

Biological volatilization of iodine from seawaters was studied using a radiotracer technique. Seawater samples were incubated aerobically in serum bottles with radioactive iodide tracer (¹²⁵I), and volatile organic and inorganic iodine were collected with activated charcoal and silver wool trap, respectively. Iodine was volatilized mainly as organic iodine, and inorganic iodine volatilization was not observed. Influence of light intensity on the volatilization was determined, but no significant differences were observed under light (70,000 lux) and dark conditions. The effect of the chemical form of iodine on the volatilization was determined, and the results suggested that volatilization preferentially occurs from iodide (I^?) but not from iodate (IO₃ ^?). Volatilization did not occur when the samples were autoclaved or filtered through a 0.22-μm pore size membrane filter. Incubation of the samples with antibiotics caused decreased volatilization. Conversely, enhanced volatilization was observed when the samples were incubated with yeast extract. Fifty-nine marine bacterial strains were then randomly isolated from marine environments, and their iodine-volatilizing capacities were determined. Among these, 19 strains exhibited significant capacities for volatilizing iodine. 16S ribosomal RNA gene comparisons indicated that these bacteria are members of Proteobacteria (α and γ subdivisions) and Cytophaga-Flexibacter-Bacteroides group. One of the strains, strain C-19, volatilized 1 to 2% of total iodine during cultivation, and the gaseous organic iodine was identified as methyl iodide (CH₃I). These results suggest that organic iodine volatilization from seawaters occurs biologically, and that marine bacteria participate in the process. Considering that volatile organic iodine emitted from the oceans causes atmospheric ozone destruction, biological iodine volatilization from seawater is of great importance. Our results also contribute to prediction of movement and diffusion of long-lived radioactive iodine (¹²⁹I) in the environment.     

Response of nodulating and non-nodulatingPisum sativum L. to nitrate

This study examined whether ‘Risnod2’ and ‘Risnod27’ non-nodulating mutants of pea (Pisum sativum L.) provided with increasing concentrations of nitrate could achieve a growth and nitrogen accumulation comparable to their parental N₂-fixing cv. Finale. In the cv. Finale, nodule number, nodule dry mass accumulation, total C₂H₂-reducing activity of nodulated roots (TAR) and estimated N₂ fixation were considerably inhibited at 5.0 and 10.0 mM root medium NO₃ ⁻ concentrations. In contrast a 0.63 mM level stimulated both the nodule dry mass and TAR. The cv. Finale N₂-fixing plants grown on 0 to 2.5 mM NO₃ ⁻ levels had higher shoot N concentrations than the Nod⁻ mutants, but within the 5.0 to 10.0 mM levels the Nod⁻ mutants approached or even overtopped the N concentration of the cv. Finale plants. Compared with a high positive correlation found in the Nod⁻ mutants, shoot N concentration in the cv. Finale was negatively correlated with the root medium NO₃ ⁻ concentration. The pattern of nitrogen content in shoot dry mass was very similar to that seen in the shoot dry mass accumulation. The Nod⁻ mutants grown on the 5.0 and/or 10.0 mM NO₃ ⁻ level had plant dry mass, shoot nitrogen concentration, shoot nitrogen content, and root/shoot dry mass ratio comparable with those of the nodulating cv. Finale grown on the same nitrate levels.     

Antioxidative system in maize roots as affected by osmotic stress and different nitrogen sources

The activities of antioxidative enzymes and contents of proline and total phenolics were assayed in roots of two maize (Zea mays L.) genotypes grown in a medium containing nitrate (NO₃ ⁻) or both nitrogen forms, nitrate and ammonium (NH₄ ⁺/NO₃ ⁻). An increase in the activities of class III peroxidases (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), ascorbate oxidase (AO) and proline content, and decrease in phenolic content were observed in NH₄ ⁺/NO₃ ⁻ in comparison with NO₃ ⁻ grown plants. When polyethylene glycol (PEG) was added to both nitrogen treatments, the content of total phenolics and proline was increased, especially in NH₄ ⁺/NO₃ ⁻ treatment. The PEG treatment decreased enzyme activities in NH₄ ⁺/NO₃ ⁻ grown plants, but in NO₃ ⁻ grown plants activities of POD and SOD were increased, opposite to decreased APX and AO. Isoelectric focusing demonstrated increased activities of acidic POD isoforms in PEG treated NO₃ ⁻ grown plants, and lower activities of both, acidic and basic isoforms in NH₄ ⁺/NO₃ ⁻grown plants.     

Nitrate and ammonium accumulation in bermudagrass in relation to nitrogen fertilization and season

Seasonal changes in nitrate and ammonium concentrations were studied inCynodon dactylon (L.) Pers. plants grown for one year in the field in a Mediterranean area. Plants cultivated in a sandy loam soil were fertilized with nitrate-N or ammonium-N at two application rates (250 and 1000 kg N ha⁻¹ year⁻¹) and compared to controls with no added N. Plots were harvested every three weeks from May to November. Shoots were separated into leaves and stems and analyses carried out in both fractions. Nitrogen applications generally led to elevated nitrate concentrations both in leaves and stems at all sampling dates but had little influence on the ammonium concentrations of the tissues. Higher nitrate and ammonium concentrations were found in stems than in leaves, although no levels higher than 0.22% NO ₃ ⁻ −N and 0.10% NH ₄ ⁺ −N were detected in either fraction. Nitrate tended to accumulate mostly in autumn and spring whereas low accumulations were found in summer. Ammonium showed both in leaves and stems a progressive but limited accumulation throughout the period with a peak in October, followed by a strong decrease in November.     

Root growth and calcium uptake in relation to calcium concentration

Summary The purpose of the present work has been to investigate the influence of calcium supply on root growth in barley. The plants were grown in pots, in which the upper part was a sand-perlite mixture and the lower part a test solution with varying calcium concentration (10⁻⁶–10⁻² M CaCl₂). The two parts were separated by a peat layer impeding a calcium transport from the upper to the lower part. The growth of the roots in the test media was examined daily by counting the total number of roots and the number of roots with laterals. The development of the number of roots had an exponential course at all calcium concentrations and was enhanced by increased calcium concentration. At harvest it was found that the size of the roots (length and dry weight) decreased with decreasing calcium concentration to a certain extent.