Effects of root temperature on uptake of nitrate and ammonium ions by barley grown in flowing-solution culture

Summary Barley plants (Hordeum vulgare L.) grown from seed for 28 days in flowing solution culture were subjected to different root temperatures (3, 5, 7, 9, 11, 13, 17, 25°C) for 14 days with a common air temperature of 25/15°C (day/night). Uptake of NH₄ and NO₃ ions was monitored separately and continuously from solutions maintained at 10 M NH₄NO₃ and pH 6.0. Effects of root temperature on unit absorption rate , flux and inflow were compared. After 5 days , and increased with temperature over the range 3–11°C for NH₄ ions and over the range 3–13°C for NO₃ ions, with little change for either ion above these temperatures. Q₁₀ temperature coefficients for NH₄ ions (3–13°C) were 1.9, 1.7 and 1.6 for , and respectively, the corresponding values for NO₃ ions being 5.0, 4.5 and 4.6. For both ions, , and changed with time as did their temperature dependence over the range 3–25°C, suggesting that rates of ontogenetic development and the extent of adaptation to temperature may have varied among treatments.     

The effect of endogenous and externally supplied nitrate on nitrate uptake and reduction in sugarbeet seedlings

The pericarp of the dormant sugarbeet fruit acts as a storage reservoir for nitrate, ammonium and -amino-N. These N-reserves enable an autonomous development of the seedling for 8–10 d after imbibition. The nitrate content of the seed (1% of the whole fruit) probably induces nitrate-reductase activity in the embryo enclosed in the pericarp. Nitrate that leaks out of the pericarp is reabsorbed by the emerging radicle. Seedlings germinated from seeds (pericarp was removed) without external N-supply are able to take up nitrate immediately upon exposure via a low-capacity uptake system (v_max = 0.8 mol NO ₃ ^- ·(g root FW)^–1·h^–1; K_s = 0.12 mM). We assume that this uptake system is induced by the seed nitrate (10 nmol/seed) during germination. Induction of a high-capacity nitrate-uptake system (v_max = 3.4 mol NO ₃ ^- ·(g root FW)^–1·h^–1; K_s = 0.08 mM) by externally supplied nitrate occurs after a 20-min lag and requires protein synthesis. Seedlings germinated from whole fruits absorb nitrate via a highcapacity uptake mechanism induced by the pericarp nitrate (748 nmol/pericarp) during germination. The uptake rates of the high-capacity system depend only on the actual nitrate concentration of the uptake medium and not on prior nitrate pretreatments. Nitrate deprivation results in a decline of the nitrate-uptake capacity (t_1/2 of v_max = 5 d) probably caused by the decay of carrier molecules. Small differences in K_s but significant differences in v_max indicate that the low- and high-capacity nitrate-uptake systems differ only in the number of identical carrier molecules.Abbreviations NR nitrate reductase - pFPA para-fluorophenylalanine This work was supported by a grant from Bundesministerium für Forschung und Technologie and by Kleinwanzlebener Saatzucht AG, Einbeck.     

Comparing different approaches to calculate the effects of heterogeneous root distribution on nutrient uptake: a case study on subsoil nitrate uptake by a barley root system

Simulation models of nutrient uptake of root systems starting with one-dimensional single root approaches up to complex three-dimensional models are increasingly used for examining the interacting of root distribution and nutrient uptake. However, their accuracy was seldom systematically tested. The objective of the study is to compare one-dimensional and two-dimensional modelling approaches and to test their applicability for simulation of nutrient uptake of heterogeneously distributed root systems giving particular attention to the impact of spatial resolution. Therefore, a field experiment was carried out with spring barley (Hordeum vulgare L. cv. Barke) in order to obtain data of in situ root distribution patterns as model input. Results indicate that a comparable coarse spatial resolution can be used with sufficient modelling results when a steady state approximation is applied to the sink cells of the two-dimensional model. Furthermore, the accuracy of the model was clearly improved compared to a simple zero sink approach assuming both near zero concentrations within the sink cell and a linear gradient between the sink cell and its adjacent neighbours. However, for modelling nitrate uptake of a heterogeneous root system a minimum number of grid cells is still necessary. The tested single root approach provided a computational efficient opportunity to simulate nitrate uptake of an irregular distributed root system. Nevertheless, two-dimensional models are better suited for a number of applications (e.g. surveys made on the impact of soil heterogeneity on plant nutrient uptake). Different settings for the suggested modelling techniques are discussed.     

The effect of nitrate concentration in a flowing solution system on growth and nitrate uptake of twoPlantago species

Summary Juvenile plants ofPlantago lanceolata andP. major ssp.major were grown in a flowing solution system at 7.5 mM or 9.5 M NO₃. The parameters investigated were: RGR, shoot weight percentage, leaf length, length of main root axis, shoot concentrations of major ions and organic N, and the specific uptake rate for NO₃. At 9.5 M NO₃ growth ofP. major was not hampered, whereas shoot growth and leaf length ofP. lanceolata were reduced. The NO₃ concentration ofP. lanceolata decreased more than that ofP. major. The different performances of the species at 9.5 M NO₃ were associated with different specific uptake rates. In both treatments the root system ofP. major was shorter than that ofP. lanceolata. P. lanceolata accumulated more NO₃ in the leaves. The performance of thePlantago species is discussed in relation to the availability of nutrients in their habitats.Grassland Species Research Group. Publication no. 37.     

The effect of indigenous vesicular-arbuscular mycorrhizal fungi on nutrient uptake and growth of barley in two Danish soils

Summary To investigate the effect of indigenous VAM fungi and of increasing the amount of natural inoculum barley was grown in containers buried in the field with uninoculated and inoculated irradiated soil and with uninoculated and inoculated untreated soil from two locations, one low and one high in available P. The experiment was set up with 3 P fertilizer applications (0, 15, 30 kg P/ha). Growth and uptake of P was measured. The inocula were prepared from natural VAM populations. VAM fungal infection was established in the irradiated soil at a lower level than in the untreated soil. VAM fungal infection was decreased by increasing P fertilizer application. In the soil low in available P VAM increased concentration of P and total uptake of P. VAM did not cause an increased growth. The reason for this may be the low establishment of VAM in the irradiated soil and/or because the indigenous VAM species were not efficient. It is also possible that a pronounced growth increase due to irradiation the soil may have masked a smaller effect of the indigenous VAM fungi. Increasing the amount of natural inoculum in the untreated soil influenced neither VAM frequency nor growth.     

Inheritance and expression of NAD(P)H nitrate reductase in barley

Summary NADH-specific and NAD(P)H bispecific nitrate reductases are present in barley (Hordeum vulgare L.). Wild-type leaves have only the NADH-specific enzyme while mutants with defects in the NADH nitrate reductase structural gene (nar1) have the NAD(P)H bispecific enzyme. A mutant deficient in the NAD(P)H nitrate reductase was isolated in a line (nar1a) deficient in the NADH nitrate reductase structural gene. The double mutant (nar1a;nar7w) lacks NAD(P)H nitrate reductase activity and has xanthine dehydrogenase and nitrite reductase activities similar to nar1a. NAD(P)H nitrate reductase activity in this mutant is controlled by a single codominant gene designated nar7. The nar7 locus appears to be the NAD(P)H nitrate reductase structural gene and is not closely linked to nar1. From segregating progeny of a cross between the wild type and nar1a;nar7w, a line was obtained which has the same NADH nitrate reductase activity as the wild type in both the roots and leaves but lacks NADPH nitrate reductase activity in the roots. This line is assumed to have the genotype Nar1Nar1nar7nar7. Roots of wild type seedlings have both nitrate reductases as shown by differential inactivation of the NADH and NAD(P)H nitrate reductases by a monospecific NADH-nitrate reductase antiserum. Thus, nar7 controls the NAD(P)H nitrate reductase in roots and in leaves of barley.Scientific Paper No. 7617, College of Agriculture Research Center and Home Economics, Washington State University, Pullman, WA, USA. Project Nos. 0233 and 0745     

Water uptake by barley roots as affected by the osmotic and matric potential in the rhizosphere

Summary The water uptake rates of roots in saline soils are depressed by the simultaneously decreasing matric and osmotic water potentials in the soil surrounding the roots (rhizospheric soil). Unfortunately there are no reliable tools available for direct measurements of the effect of decreasing water potentials in the rhizospheric soil on the uptake rate of soil water by roots. This paper presents some results of a vegetation technique for studying the effect of different combinations of osmotic and matric water potentials in the rhizospheric soil on the water uptake rates of barley roots. Water uptake rates were reduced to a greater extent by decreasing soil matric water potentials than by decreasing soil osmotic water potentials. According to the results of this experiment, there was no relationship between the total soil water potential of a sandy soil and the water uptake rates when the roots were exposed to different combinations of and .     

Genetic mapping of the barley nitrate reductase-deficient nar1 and nar2 loci

Summary The nar2 locus that codes for a protein involved in molybdenum cofactor function in nitrate reductase and other molybdoenzymes was mapped to barley chromosome 7. F₂ genotypic data from F₃ head rows indicated nar2 is located 8.4±2.1 and 23.0± 4.6 cm from the narrow leaf dwarf (nld) and mottled seedling (mt2) loci, respectively. This locates the nar2 locus at 54.7±3.1 cm from the short-haired rachilla (s) locus near the centromere of chromosome 7. Close linkage of nar2 with DDT resistance (ddt) and high lysine (lys3) loci was detected but could not be quantified due to deviations from the individual expected 121 segregations for the ddt and lys3 genes. Southern blots of wheat-barley addition lines probed with a nitrate reductase cDNA located the NADH : nitrate reductase structural gene, nar1, to chromosome 6.Scientific Paper No. 7762. College of Agriculture and Home Economics Research Center, Washington State University, Project No. 0745. This investigation was supported in part by United States Department of Agriculture Grant No. 86-CRCR-1-2004     

The impact of salt stress on the water status of barley plants is partially mitigated by elevated CO2

With the changing climate, plants will be facing increasingly harsh environmental conditions marked by elevated salinity in the soils and elevated concentrations of CO₂ in the atmosphere. These two factors have opposite effects on water status in plants. Therefore, our objective was to determine the interaction between these two factors and to determine whether elevated [CO₂] might alleviate the adverse effects of salt stress on water status in two barley cultivars, Alpha and Iranis, by studying their relative water content and their water potential and its components, transpiration rate, hydraulic conductance, and water use efficiency. Both cultivars maintained their water status under salt stress, increasing water use efficiency and conserving a high relative water content by (1) reducing water potential via passive dehydration and active osmotic adjustment and (2) decreasing transpiration through stomatal closure and reducing hydraulic conductance. Iranis showed a greater capacity to achieve osmotic adjustment than Alpha. Under the combined conditions of salt-stress and elevated [CO₂], both cultivars (1) achieved osmotic adjustment to a greater extent than at ambient [CO₂], likely due to elevated rates of photosynthesis, and (2) decreased passive dehydration by stomatal closure, thereby maintaining a greater turgor potential, relative water content, and water use efficiency. Therefore, we found an interaction between salt stress and elevated [CO₂] with regard to water status in plants and found that elevated [CO₂] is associated with improved water status of salt-stressed barley plants.     

The effect of selenium on sulfur uptake by barley and rice

Because of their chemical and physical similarities, plant uptake of S and Se are closely related. Barley (Hordeum vulgare L.) and rice (Oryza sativa L.) were grown in greenhouse solution culture to examine the synergistic interactions between SO₄ and Se⁶⁺ in plant uptake. In the presence of low concentrations of solution SO₄, shoot and root yields were decreased with additions of Se⁶⁺. However, when SO₄ was present in elevated concentrations, no Se-induced yield reduction occurred. A synergistic interaction between SO₄ and Se⁶⁺ caused an increase in the shoot S concentrations with increasing concentrations of Se⁶⁺ at low SO₄ solution concentrations. At elevated SO₄ concentrations, no synergism was osberved. Selenium had a lesser effect on the S concentration in plant roots.     

The Effects of NaCl Treatment on Water Relations, Growth, and ABA Content in Barley Cultivars Differing in Drought Tolerance

Changes in transpiration and stomatal conductance and other characteristics of water relations, growth rate, and ABA content have been followed in short- and long-term experiments in two barley cultivars (cv. Michaelovsky and cv. Prairie) with contrasting drought resistance characteristics. The aim of this work was to reveal the importance of stomatal behavior in salt tolerance and also the involvement of ABA in its control. Salinity stress brought about a reduction in stomatal conductance in both cultivars, but the effect was initially more pronounced in the drought-tolerant cv. Prairie than in the drought-sensitive cv. Michaelovsky. The difference between the two cultivars changed with time, and later on transpiration and stomatal conductance became higher in Prairie than in Michaelovsky. In both the short and the long term, the extent of stomatal closure due to salinity correlated with the level of ABA accumulation in the leaves of the plants. Fast stomatal closure was likely to be responsible for growth resumption after an initial arrest by salt treatment and for the maintenance of extension growth later on, thus enabling its higher rate in Prairie than in Michaelovsky plants. Leaves of Prairie accumulated less toxic chloride ions, which may be the result of a lower transpiration rate observed during the first phase of salt treatment. A subsequent increase in stomatal conductance observed in Prairie is likely to ameliorate their gas exchange and maintain photosynthesis and growth. Thus, differences between the cultivars in the stomatal response to salinity changed with time, which may be why there are discrepancies in the attempts to relate stomatal conductance to salt tolerance observed in literature.     

Effect of nitrate pulses on the nitrate-uptake rate,synthesis of mRNA coding for nitrate reductase,and nitrate-reductase activity in the roots of barley seedlings

Using pulses of nitrate, instead of the permanent presence of external nitrate, to induce the nitrate-assimilating system in Hordeum vulgare L., we demonstrated that nitrate can be considered as a trigger or signal for the induction of nitrate uptake, the appearance of nitratereductase activity and the synthesis of mRNA coding for nitrate reductase. Nitrate pulses stimulated the initial rate of nitrate uptake, even after subsequent cultivation in N-free medium, and resulted in a higher acceleration of the uptake rate in the presence of nitrate than in its absence.Abbreviations NR nitrate reductase     

Nitrate and nitrite uptake and reduction by intact sunflower plants

Nitrogen-starved sunflower plants (Helianthus annuus L. cv. Peredovic) cannot absorb NO ₃ ^– or NO ₂ ^– upon initial exposure to these anions. Ability of the plants to take up NO ₃ ^– and NO ₂ ^– at high rates from the beginning was induced by a pretreatment with NO ₃ ^– . Nitrite also acted as inducer of the NO ₂ ^– -uptake system. The presence of cycloheximide during NO ₃ ^– -pretreatment prevented the subsequent uptake of NO ₃ ^– and NO ₂ ^– , indicating that both uptake systems are synthesized de novo when plants are exposed to NO ₃ ^– . Cycloheximide also suppressed nitrate-reductase (EC 1.6.6.1) and nitrite-reductase (EC 1.7.7.1) activities in the roots. The sulfhydryl-group reagent N-ethylmaleimide greatly inhibited the uptake of NO ₃ ^– and NO ₂ ^– . Likewise, N-ethylmaleimide promoted in vivo the inactivation of nitrate reductase without affecting nitrite-reductase activity. Rates of NO ₃ ^– and NO ₂ ^– uptake as a function of external anion concentration exhibited saturation kinetics. The calculated K_m values for NO ₃ ^– and NO ₂ ^– uptake were 45 and 23 M, respectively. Rates of NO ₃ ^– uptake were four to six times higher than NO ₃ ^– -reduction rates in roots. In contrast, NO ₂ ^– -uptake rates, found to be very similar to NO ₃ ^– -uptake rates, were much lower (about 30 times) than NO ₂ ^– -reduction rates. Removal of oxygen from the external solution drastically suppressed NO ₃ ^– and NO ₂ ^– uptake without affecting their reduction. Uptake and reduction were also differentially affected by pH. The results demonstrate that uptake of NO ₃ ^– and NO ₂ ^– into sunflower plants is mediated by energy-dependent inducible-transport systems distinguishable from the respective enzymatic reducing systems.Abbreviations CHI cycloheximide - NEM N-ethylmaleimide - NiR nitrite reductase - NR nitrate reductase - pHME p-hydroxymercuribenzoate This research was supported by grant PB86-0232 from the Dirección General de Investigatión Científica y Técnica (Spain). One of us (E.A.) thanks the Consejeria de Educación y Ciencia de la Junta de Andalucia for the tenure of a fellowship. We thank Miss G. Alcalá and Miss C. Santos for their valuable technical and secretarial assistance.     

Ammonium and nitrate uptake by barley genotypes in diurnally fluctuating root temperatures simulating till and no-till conditions

The morphological development and N uptake patterns of spring barley (Hordeum vulgare L.) genotypes of Northern European (Nordic) and Pacific Northwest US (PNW) origin were compared under two diurnally fluctuating root temperature regimes in solution culture. The two regimes, 15/5°C and 9/5°C day maximum/night minimum temperatures, simulated soil temperature differences between tilled vs. heavy-residue, no-till conditions, respectively, observed during early spring in eastern Washington. Previous field experiments indicated that some of the Nordic genotypes accumulated more N and dry matter than the PNW cultivars during early spring under no-till conditions. The objective of this experiment was to determined whether these differences 1) are dependent on the temperature of the rooting environment, and 2) are correlated with genotypic differences in NH₄ ⁺ and NO₃ ^– uptake. Overall, shoot N and dry matter accumulation was reduced by 40% due to lower root temperatures during illumination. Leaf emergence was slowed by 14 to 22%, and tiller production was also inhibited. All genotypes absorbed more ammonium than nitrate from equimolar solutions, and the proportion of total N absorbed as NH₄ ⁺ was slightly higher in the 9/5°C than the 15/5°C regime. A Finnish genotype, HJA80201, accumulated significantly more shoot N than the PNW cultivars, Clark and Steptoe, and also more than a Swedish cultivar, Pernilla, in the 9/5°C regime. In the 15/5°C regime Steptoe did not differ in shoot N from the Nordic genotypes, while Clark remained significantly lower. These differences were not correlated to relative propensity for N form. Root lengths of the Nordic genotypes were significantly greater than the PNW genotypes grown under the 9/5°C regime, while the root lengths in the warmer root temperture regime were not significantly different among genotypes. Higher root elongation rates under low soil temperature conditions may be an inherent adaptive mechanism of the Nordic genotypes. Overall, the data indicate that lower maximum daytime temperatures of the soil surface layer likely account for a significant portion of the growth reductions and lower N uptake observed in no-till systems.     

The effects of salinity and osmotic stress on barley germination rate: sodium as an osmotic regulator

Background and Aims

Seed germination is negatively affected by salinity, which is thought to be due to both osmotic and ion-toxicity effects. We hypothesize that salt is absorbed by seeds, allowing them to generate additional osmotic potential, and to germinate in conditions under which they would otherwise not be able to germinate.

Methods

Seeds of barley, Hordeum vulgare, were germinated in the presence of either pure water or one of five iso-osmotic solutions of polyethylene-glycol (PEG) or NaCl at 5, 12, 20 or 27 °C. Germination time courses were recorded and germination indices were calculated. Dry mass, water content and sodium concentration of germinating and non-germinating seeds in the NaCl treatments at 12 °C were measured. Fifty supplemental seeds were used to evaluate the changes in seed properties with time.

Key Results

Seeds incubated in saline conditions were able to germinate at lower osmotic potentials than those incubated in iso-osmotic PEG solutions and generally germinated faster. A positive correlation existed between external salinity and seed salt content in the saline-incubated seeds. Water content and sodium concentration increased with time for seeds incubated in NaCl. At higher temperatures, germination percentage and dry mass decreased whereas germination index and sodium concentration increased.

Conclusions

The results suggest that barley seeds can take up sodium, allowing them to generate additional osmotic potential, absorb more water and germinate more rapidly in environments of lower water potential. This may have ecological implications, allowing halophytic species and varieties to out-compete glycophytes in saline soils.     

Stable transformation of barley via PEG-induced direct DNA uptake into protoplasts

Summary Protoplasts isolated from a barley cell suspension (cv Dissa) were transformed with plasmid DNA containing the neomycinphosphotransferase II (NPT) and -glucuronidase (GUS) genes, using polyethyleneglycol (PEG) to induce DNA uptake. Transformed microcalli were selected in media containing G418 sulphate. NPT activity was detected in all antibiotic-resistant cell lines, but not all NPT-positive cell lines had GUS activity. Southern analysis confirmed the presence of sequences homologous to the APT and GUS genes in DNA of G418-resistant callus.     

Effects of temperature on parameters of root growth relevant to nutrient uptake: Measurements on oilseed rape and barley grown in flowing nutrient solution

Summary Effects of root temperature on the growth and morphology of roots were measured in oilseed rape (Brassica napus L.) and barley (Hordeum vulgare L.). Plants were grown in flowing solution culture and acclimatized over several weeks to a root temperature of 5°C prior to treatment at a range of root temperatures between 3 and 25°C, with common shoot temperature. Root temperature affected root extension, mean radius, root surface area, numbers and lengths of root hairs. Total root length of rape plants increased with temperature over the range 3–9°C, but was constant at higher temperatures. Root length of barley increased with temperature in the range 3–25°C, by a factor of 27 after 20 days. Root radii had a lognormal distribution and their means decreased with increasing temperature from 0.14 mm at 3°C to 0.08 mm at 25°C. The density of root hairs on the root surface increased by a factor of 4 in rape between 3 and 25°C, but in barley the highest density was at 9°C. The contribution of root hairs to total root surface area was relatively greater in rape than in barley. The changes in root system morphology may be interpreted as adaptive responses to temperature stress on nutrient uptake, providing greater surface area for absorption per unit root weight or length.     

Relationships between external nitrate availability,nitrate uptake and expression of nitrate reductase in roots of barley grown in N-limited split-root cultures

Despite the large number of studies of nitrate metabolism in plants, it remains undetermined to what extent this key plant system is controlled by overall plant N nutrition on the one hand, and by the nitrate ion itself on the other hand. To investigate these questions, V _max for nitrate uptake (high-affinity range), and nitrate reductase (NR) mRNA and activity, were measured in roots of N-limited barley (Hordeum vulgare L. cv. Golf) grown under conditions of constant relative addition of nitrate, with the seminal roots split between two culture compartments. The total amount of nitrate added per unit time (0.09·d^-1) was distributed between the two root parts (subroots) in ratios of 1000, 982, 955, 9010, 8020, and 5050. These nitrate-addition ratios resulted in nitrate fluxes ranging from 0 to 23 mol nitrate·g^-1 DW root·h^-1, while the external nitrate concentrations varied between 0 and 1.2 M. The apparent V _max for net nitrate uptake showed saturation-type responses to nitrate flux maintained during preceding growth. The flux resulting in half-maximal induction of nitrate uptake was approximately 4 mol nitrate·g^-1 DW root·h^-1, corresponding to an external nitrate concentration of 0.7 M. The activity of NR and levels of NR mRNA did not saturate within the range of nitrate fluxes studied. None of the parameters studied saturated with respect to the steady-state external nitrate concentration. At the zero nitrate addition — the 0%-root — initial uptake activity as determined in short-term ¹⁵N-labelling experiments was insignificant, and NR activity and NR mRNA were not detectable. However, nitrate uptake was rapidly induced, showing that the 0%-root had retained the capacity to respond to nitrate. These results suggest that local nitrate availability has a significant impact on the nitrate uptake and reducing systems of a split-root part when the total plant nitrate nutrition is held constant and limiting.Abbreviation NR nitrate reductase This work was supported by the Lars Hierta Memory Foundation, the Royal Swedish Academy of Sciences, and by the Swedish Natural Science Research Council via project grants (to C.-M.L. and B.I.) and visiting scientist grant (to W.H.C.). We thank Mrs. Ellen Campbell for technical advice, and Mrs. Judith V. Purves, Long Ashton Research Station, Long Ashton, UK, for analyses of ¹⁵N-labelling in tissue samples.     

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.