Changes in the uptake and assimilation efficiency for sulfate and nitrate in maize hybrids selected during the period 1930 through 1975

Sulfate and nitrate uptake capacity, ATP sulfurylase (ATPS) and nitrate reductase (NR) activity were determined in a set of maize hybrids representative of selection cycles carried out during the period 1930 through 1975. All the above metabolic parameters together with the grain yield were improved by the selection. The annual rate of the improvement was higher (double) for sulfate uptake than for ATPS and similar for NR and nitrate uptake. Significant correlations were evidenced between the uptake efficiency of the roots and the enzyme activity in the leaves both for sulfate and nitrate pathways, and also between the uptake and enzyme steps of nitrate and those of sulfate. This offered good evidence of a coupled genetic regulation between nitrogen and sulfur metabolism in maize.     

Uptake and translocation of calcium in cucumber

Uptake and translocation of Ca²⁺(⁴⁵Ca) were compared with water translocation in 12-day old intact plants and excised roots of cucumber ( Cucumis sativus L. var. Cilla), which had been cultivated in nutrient solution. No immediate reduction of Ca²⁺ uptake was found when water translocation was reduced by excision of the shoot. In the presence of 2,4-dinitrophenol Ca²⁺ translocation was reduced in the intact plants while water translocation was unchanged. It is suggested that regulation of Ca²⁺ uptake is primarily achieved in the root. The DNP-sensitive mechanism of Ca²⁺ uptake was associated with the root and probably represented transport through the endodermis into the stele.     

Pattern of sulfate uptake during root elongation in maize: its correlation with productivity

The efficiency of sulfate uptake was evaluated in excised roots of 22 maize genotypes, 12 inbreds and 10 hybrids, in order to study the relationship between the kinetic characteristics of the uptake and the grain productivity. During root elongation, the uptake capacity showed a pulse which appeared when the root reached 1/3 to 1/2 of its final length. The size of the accumulated pool of sulfate was significantly correlated with the productivity. The kinetic parameters of the uptake, Vmax and Km, followed the same trend, showing pulses, whoxe maximum had the same position for Vmax and Km in each genotype. The variability with the genotype of the size and duration of the Vmax pulse was not strictly connected with that of Km. The main correlation between Vmax and Km patterns was the following; inbreds were generally characterized by low Vmax and low Km; hybrids by high Vmax and high Km. As a consequence, in most cases, the benefit of the heterotic stimulation of Vmax was contrasted by the loss of affinity of the transport system or the nutrients.     

Demand-Driven Control of Root ATP Sulfurylase Activity and SO42- Uptake in Intact Canola (The Role of Phloem-Translocated Glutathione)

The activity of ATP sulfurylase extracted from roots of intact canola (Brassica napus L. cv Drakkar) increased after withdrawal of the S source from the nutrient solution and declined after refeeding SO42- to S-starved plants. The rate of SO42- uptake by the roots was similarly influenced. Identical responses were obtained in SO42- -fed roots when one-half of the root system was starved for S. The internal levels of SO42- and glutathione (GSH) declined after S starvation of the whole root system, but only GSH concentration declined in +S roots of plants from split root experiments. The concentration of GSH in phloem exudates decreased upon transfer of plants to S-free solution. Supplying GSH or cysteine to roots, either exogenously or internally via phloem sap, inhibited both ATP sulfurylase activity and SO42- uptake. Buthionine sulfoximine, an inhibitor of GSH synthesis, reversed the inhibitory effect of cysteine on ATP sulfurylase. It is hypothesized that GSH is responsible for mediating the responses to S availability. ATP sulfurylase activity and the SO42- uptake rate are regulated by similar demand-driven processes that involve the translocation of a phloem-transported message (possibly GSH) to the roots that provides information concerning the nutritional status of the leaves.     

Effect of light intensity on proton extrusion by roots of intact maize plants

Shading of maize plants ( Zea mays L. cv. Blizzard) reduced net H⁺ extrusion by roots and increased K⁺ release, whereas there was no significant effect on anion efflux in deionized water. With lower light intensity the concentrations of carbohydrates in the roots decreased, but ATP levels and energy charge remained unchanged. Also, shading raised the tissue pH of roots and made the cytoplasmic pH of root cells drop. There was a significant influence of light intensity on H⁺ uptake by roots from an acidified test solution and CCCP (carbonylcyanide-3-chlorophenylhydrazone)-in-duced H⁺ uptake was modified by shading.
It is concluded that low light intensity does not limit active H⁺ release by plasmalemma ATPase activity in the root cells, but that a reduced carbohydrate supply brings about a change in biochemical reactions which alter the membrane permeability for protons. An increased passive reflux of H⁺ into the cells rather than a reduced H⁺ ATPase activity explains the decrease of net H⁺ release by roots of intact maize plants under low light intensity.     

An effect of Na+ on K+ uptake in intact seedlings of Zea mays

Models for the regulation of K⁺ uptake in higher plant roots have become more complex as studies have moved from the level of excised low-salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.
The uptake of K⁺ by low-salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na⁺ concentration over a wide range. However, independence of Na⁺ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na⁺ in the uptake medium enhanced K⁺ uptake. In the presence of Na⁺, K⁺ uptake rates were similar in whole plants with high root K⁺ contents to rates in excised or intact, low-salt roots.     

2,4-Dichlorophenoxyacetic acid inhibition of potassium transport in barley seedlings

Growth, potassium uptake and translocation as well as transpiration rates were measured in intact low-salt barley seedlings ( Hordeum vulgare L. cv. Union) in the presence of different 2,4-D concentrations at pH 6.5. Growth was only affected at 10^-3 M .
Above 10^-7 M 2,4-D both uptake by the roots and transport to the shoots were inhibited. The inhibition at 10^-5 M remained constant for at least 24 h. Furthermore inhibition of uptake was measurable within 1 h. Excised roots and roots of intact plants showed the same uptake pattern.
It is suggested that the observed effects were caused by 2,4-D-induced changes in uptake and translocation systems in the roots. Pre-treatment with 10^-5 M 2,4-D had no effect upon subsequent potassium uptake. Transpiration was reduced within 1 h in 10^-4 or 10^-3 M 2,4-D, probably due to changes in water transport or root permeability.     

Effect of root perturbation and excision on nitrate influx and efflux in barley (Hordeum vulgare) seedlings

The effects of perturbation and excision on net NO^-₃, uptake, influx and efflux in roots of 8-day-old barley ( Hordeum vulgare L.) seedlings induced with NO^-₃ or NO^-₂ were determined. Perturbation was simulated by mechanically striking the intact roots with a glass rod. Perturbation or excision of roots and subsequent division into small segments had little effect on NO^-₃ influx, but briefly inhibited net uptake which recovered within a few min. While in perturbed roots net uptake rates recovered to the same level as in control roots, full recovery did not occur in excised roots. Inhibition of net uptake was due to stimulation of NO^-₃ efflux. The recovery time and level of inhibition of net NO^-₃ uptake and/or stimulation of efflux were a function of extent of perturbation, or the number of segments following excision, and root NO^-₃ concentration. NO^-₃ efflux was further stimulated when roots were perturbed after cytoplasmic NO^-₃ had been depleted, indicating that both the plasmalemma and tonoplast may be affected. In excised roots both NO^-₃ influx and efflux decreased with age due to depletion of energy sources. The results indicate that root perturbation and excision had no effect on NO^-₃ influx but inhibited net uptake by stimulating efflux.     

Effect of gibberellic acid on K+ (Rb+) uptake and transport in sunflower roots

Four-week-old sunflower plants ( Helianthus annuus L. cv. Halcón), grown in different nutrient solutions, were used to study the effects of gibberellic acid (GA₃) on K⁺ (Rb⁺) uptake by roots or transport to the shoot. Gibberellic acid application to the nutrient solution did not affect the exudation process of excised roots. When GA₃ was sprayed on leaves 2 to 6 days before excising the roots, the rate of exudation and the K⁺ flux increased. When the exudation study was done keeping the roots in a nutrient solution in which Rb⁺ replaced K⁺, the GA₃ effects were evident also on Rb⁺ uptake and transport. In intact plants, GA₃ increased the Rb⁺ transported to the shoot but did not affect Rb⁺ accumulation in the root. It is suggested that these GA₃ effects can be explained if it is assumed that GA₃ acts on the transport of ions to the xylem vessels.     

玉米ST和ATPS部分cDNA序列克隆及分析

硫酸盐转运蛋白(ST)和ATP硫酸化酶(ATPS)是根系吸收硫酸盐和植物体内硫酸盐同化过程的关键蛋白和酶,在硫酸盐的生物转运过程中具有重要作用.以水培玉米农大108根系为材料,并根据已报道的玉米的硫酸盐转运蛋白和ATP硫酸化酶基因保守序列分别设计PCR引物对,采用RT-PCR方法克隆到783 bp和820 bp的部分硫酸盐转运蛋白和ATP硫酸化酶cDNA片段,分别命名为ST_ND108和ATPS_ND108.序列分析和比对结果显示,ST_ND108与已报道的玉米和水稻的高亲和型硫酸盐转运蛋白基因同源性分别为99%和85%;而ATPS_ND108与已报道的玉米ATP硫酸化酶基因同源性达到97%,进化树聚类分析和预测氨基酸的BLAST结果证实ST_ND108为高亲和性硫酸盐转运蛋白基因片段,ATPS_ND108为质体ATP硫酸化酶基因片段.     

Ammonium uptake by field-grown Eriophorum vaginatum roots under laboratory and simulated field conditions

Nitrogen (N) deficiencies in tundra ecosystems could be caused, in part, by the kinetics of root N uptake. The objectives of this study were to quantify NH₄ uptake by field-grown excised roots of Eriophorum vaginatum I. under controlled NH₄ concentrations (0-250 μmol I^-1) and temperatures (5-20°C) and to evaluate this laboratory derived model as a means of estimating field NH₄ uptake. There was no consistent temperature effect on root NH₄ uptake which suggests a relative in-sensitivity of E. vaginatum roots to short-term temperature fluctuations. The Michaelis-Menten equation parameters for NH₄ uptake were V_max= 22.1 μmol h^-1 g^-1 and K_m= 191 μmol I^-1. Using field NH₄ concentrations, field E. vaginatum root biomass data, and the Michaelis-Menten equation, an estimate was made of NH₄ uptake over a 42 day period; this estimate of NH₄ uptake accounted for 28% of the net incorporation of N into leaves and roots which is a reasonable estimate for E. vaginatum which relies primarily on N retranslocation for supplying new leaves and roots. Major uncertainties in field N uptake rates, model parameterization, and site characterization preclude an accurate model validation and indicate research areas most in need of future study.     

Cloning of a cDNA encoding ATP sulfurylase from Arabidopsis thaliana by functional expression in Saccharomyces cerevisiae.

ATP sulfurylase, the first enzyme in the sulfate assimilation pathway of plants, catalyzes the formation of adenosine phosphosulfate from ATP and sulfate. Here we report the cloning of a cDNA encoding ATP sulfurylase (APS1) from Arabidopsis thaliana. APS1 was isolated by its ability to alleviate the methionine requirement of an ATP sulfurylase mutant strain of Saccharomyces cerevisiae (yeast). Expression of APS1 correlated with the presence of ATP sulfurylase enzyme activity in cell extracts. APS1 is a 1748-bp cDNA with an open reading frame predicted to encode a 463-amino acid, 51,372-D protein. The predicted amino acid sequence of APS1 is similar to ATP sulfurylase of S. cerevisiae, with which it is 25% identical. Two lines of evidence indicate that APS1 encodes a chloroplast form of ATP sulfurylase. Its predicted amino-terminal sequence resembles a chloroplast transit peptide; and the APS1 polypeptide, synthesized in vitro, is capable of entering isolated intact chloroplasts. Several genomic DNA fragments that hybridize with the APS1 probe were identified. The APS1 cDNA hybridizes to three species of mRNA in leaves (1.85, 1.60, and 1.20 kb) and to a single species of mRNA in roots (1.85 kb).     

SO2 and assimilatory sulfate reduction in beech leaves

The effect of SO₂ on the extractable activity of ATP sulfurylase (EC 2.7.7.4.). adenosine 5'-phosphosulfate sulfotransferase, ribulosebisphosphate carboxylase, chlorophyll, protein, sulfate, and amino acids was examined in leaves of potted grafts of beech ( Fagus sylvatica L.) treated in outdoor fumigation chambers. Addition of 0.025 and 0.075 μl SO₂ 1⁻¹ to unfiltered ambient air caused a decrease in the extractable activity of adenosine 5'-phosphosulfate sulfotransferase to about 20 to 30% of the controls. Neither the extractable activity of ATP sulfurylase and ribulosebisphosphate carboxylase nor the content in chlorophyll, total amino acids and protein were significantly affected by SO₂, but there was an increase in the sulfate content. Leaves treated with 0.075 μl SO₂ 1⁻¹ contained more alanine and cysteine and less serine than the controls. After transfer of the SO2-treated beech trees to control chambers there was an increase in adenosine 5'-phosphosulfate sulfotransferase activity, but no significant decrease in SO₂₋⁴-sulfur.     

Potassium transport in wheat seedlings grown with different potassium supplies.

The K⁺(⁸⁶Rb) uptake into the roots and the translocation to the shoots of 11-day-old intact wheat seedlings ( Triticum aestivum L. cv. Martonvásári 8) were investigated using plants grown with different K⁺ supplies. The effects of environmental conditions (darkness, humidity) and of metabolic and transport inhibitors (oligomycin, disalicylidene-propanediamine, 2,4-dinitriphenol, diethylstilbestrol, colchicine) were also studied. Plants with K content of about 0.2 mmol/g dry weight in the root and 0.5 mmol/g dry weight in the shoot (low K status) showed high K⁺ uptake into the roots and high translocation rates to the shoots. Both transport processes were very low in plants with K content of more than 1.5 and 2.2 mmol/g dry weight in the root and shoot, respectively (high K status).
Darkness and a relative humidity of the air of 100% did not influence K⁺ uptake by roots, but did inhibit upward translocation and water transport. Inhibition of photosynthesis and treatments with diethylstilbestrol (10⁻⁵ mol/dm³), as well as with colchicine resulted in inhibition of translocation in plants of low K status, but these inhibitors had little effect on K⁺ uptake by the roots. Oligomycin, 2,4-dinitrophenol and diethylstilbestrol (10⁻⁴ mol/dm³), however, inhibited K⁺ uptake by the roots. In general, K⁺ transport processes were almost unchanged in plants of high K status. It is concluded that only plants of low K status operating with active K⁺ transport mechanisms are responsive to environmental factors. In high K⁺ plants the transport processes are passive and are uncoupled from the metabolic energy flow.     

A comparison of NH4+ and NO3– net fluxes along roots of rice and maize

Net fluxes of NH₄⁺ and NO₃^– along adventitious roots of rice ( Oryza sativa L.) and the primary seminal root of maize ( Zea mays L.) were investigated under nonperturbing conditions using ion-selective microelectrodes. The roots of rice contained a layer of sclerenchymatous fibres on the external side of the cortex, whereas this structure was absent in maize. Net uptake of NH₄⁺ was faster than that of NO₃^– at 1 mm behind the apex of both rice and maize roots when these ions were supplied together, each at 0·1 mol m^–3. In rice, NH₄⁺ net uptake declined in the more basal regions, whereas NO₃^– net uptake increased to a maximum at 21 mm behind the apex and then it also declined. Similar patterns of net uptake were observed when NH₄⁺ or NO₃^– was the sole nitrogen source, although the rates of NO₃^– net uptake were faster in the absence of NH₄⁺. In contrast to rice, rates of NH₄⁺ and NO₃^– net uptake in the more basal regions of maize roots were similar to those near the root apex. Hence, the layer of sclerenchymatous fibres may have limited ion absorption in the older regions of rice roots.     

Influence of indole-butyric acid, boron, myo-inositol, vitamin D2 and seedling age on adventitious root development in cuttings of Phaseolus aureus

Adventitious roots develop in stem cuttings of Phaseolus aureus Roxb. seedlings when treatment with indole-butyric acid (IBA) is followed by treatment with boron. Root development varies according to the age of seedlings from which cuttings are taken. Increased root number is associated with expansion of the first leaf pair but subsequently declines, whereas root growth increases with increasing seedling age. Removal of leaves furing the first 72 h of treatment impairs root initiation whereas root growth is diminished by removal of leaves at any time during the first 120 h of treatment. IBA stimulates movement of ¹⁴C-IAA out of leaves. Vitamin D₂ and myo-inositol stimulate rooting of intact cuttings provided cuttings are subsequently supplied with boron. Hypocotyls excised from cuttings pretreated with IBA develop roots in response to myo-inositol in the absence of boron. It is proposed that endogenous auxin, arising in the leaves, and myo-inositol have roles in root initiation whilst the role of boron is suggested as one of initiating or maintaining transport from the leaves.     

Inhibition of sulphur redistribution into new leaves of vegetative soybean by excision of the maturing leaf

When soybean plants are pulsed with [³⁵S]sulphate, label is subsequently redistributed from the roots to the leaves. This confounds studies to measure the redistribution of label from leaves. Accordingly, soybean plants ( Glycine max [L.] Merr. cv. Stephens) were grown in 20 μ M sulphate and a small portion of the root system (donor root) was pulsed with [³⁵S]sulphate for 24 h. After removing the donor root, the plants were transferred into unlabelled solution, either without sulphate (S20→SO) or with 20 μ M sulphate (S20→20) (intact plants). Also at this time, the expanding leaf (L3) was excised from half of the plants in each treatment (excised plants). Immediately after the pulse, only ca 15% of the label occurred in the roots and ca 40% in the expanding leaf, L3, mostly in the soluble fraction. In intact S20→20 plants, ³⁵S-label was exported from the soluble fraction of L3, mostly as sulphate, whilst L4 and L5 imported label. Similar responses occurred in S20→SO plants except that export of label from L3 was more rapid. Excision of L3 from S20→S20 plants inhibited labelling of leaves L4-L6 but not total sulphur, whereas in S20→SO plants, excision of L3 inhibited the import of both total sulphur and ³⁵S-label in leaves L4, L5 and L6. The data suggest that the soluble fraction of almost fully expanded leaves is an important reserve of sulphur for redistribution to growing leaves. The ³⁵S-label in the root system exhibited fluctuations consistent with its proposed role in the recycling of soluble sulphur from the leaves.     

Determination of the surface area of fine tomato roots via cation uptake experiments

A method is described by which the surface area of a root is estimated from cation uptake data. ²⁴Na⁺ was supplied to excised roots of tomato ( Lycopersicon esculentum Mill, cv. Tiny Tim) seedlings at 3 μ M in unstirred solution. Coarse roots, for which external surface area and specific gravity could be measured accurately, were used to estimate the thickness (d_N) of the Nernst boundary layer at the root surface. ²⁴Na⁺ uptake (J₁) was measured by γ-ray spectroscopy. J_t and d_N were used to calculate the total surface area for ion absorption in fine roots, assuming that Na uptake rate was diffusion-limited. The results were compared to data obtained by conventional methods and indicated the usefulness of the cation uptake technique for quantitative estimates of root surfaces.     

Sulfate transport of excised roots as an index of genotype response to herbicides

The inhibitory action of four herbicides (atrazine, dalapon, moiinate, propanil) on the membrane transport of sulfate by excised roots was evaluated in tolerant ( Oryza saliva ) and susceptible ( Pisam sativum, Hordeum vulgare ) cultivated species, and in a tolerant and susceptible variety of a weed ( Brassica rapa ). A parallelism between the response of the root transport activity and the general response of the genotype was ascertained, irrespective of the metabolic target of the herbicide. The inhibition mechanism of sulfate uptake was either competitive, non competitive, or uncompetitive, but this aspect was not correlated with the response of the genotype to the herbicide. The kinetics of absorption ¹⁴C atrazine by excised roots and by chloroplasts of Brassica rapa were strictly related: the amount of atrazine binding to roots and to chloroplasts was higher in the susceptible than in the resistant variety. The Sevel of atrazine inhibition of sulfate transport in roots was correlated to that of the Hill reaction; both were higher in the susceptible variety. The membrane transport within the roots appears to summarize and anticipate the metabolic response of genotypes to herbicides.     

Uptake kinetics of iron-phytosiderophores in two maize genotypes differing in iron efficiency

Iron inefficiency in the maize ( Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe-phytosiderophores. To characterize this defect further, the uptake kinetics of Fe-phytosiderophores in ysl was compared to the Fe-efficient maize cultivar Alice. Short-term uptake of ⁵⁹Fe-labeled Fe-deoxymugineic acid (Fe-DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe-deficient plants followed Michaelis-Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe-phytosiderophores. The saturable component had similar K_m (∼ 10 μM) in both genotypes. In contrast. V_max was 5.5 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in Alice, but only 0.6 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in _ysl. Uptake experiments with double-labeled ⁵⁹Fe-[¹⁴C]DMA suggest that in both cultivars Fe-DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high-affinity and a low-affinity uptake system mediating Fe-phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high-affected uptake and led to a decrease in activity and/or number of Fe-phytosiderophore transporters.