Translocation of iron citrate and phosphorus in xylem exudate of soybean

Soybean plants, Glycine max (L.) Merrill, in standard solution received 2.5 μm ferric ethylenediamine di(o-hydroxyphenylacetate (FeEDDHA) and 0 to 128 μm phosphorus. Their stem exudates contained: 32 to 52 μm Fe, 120 to 5000 μm P, and 120 to 165 μm citrate. Electrophoresis of exudates with high P caused Fe trailing that precluded identification of any major form of Fe. Exudate with low P gave an anodic band of Fe citrate as the major Fe compound. Phosphate added to exudate in vitro depressed the Fe citrate peak and cause Fe trailing. EDDHA added to exudate in vitro pulled Fe from Fe citrate; citrate then migrated as a slower form and Fe migrated as FeEDDHA. A modified preculture system, involving 2-day renewals of 0.2 μm FeEDDHA with 3.2, 9.6, or 16 μm P and low levels of other ions, controlled pH depression and produced considerable change in citrate and P levels. The exudates contained: 45 to 57 μm Fe, 200 to 925 μm P, and 340 to 1025 μm citrate. The high citrate was from plants grown with low P. The major form of Fe in the exudates was Fe citrate. This is probably the form translocated in the plants.     

Absorption and transfer of fe and mn in germinating sorghum

The absorption of Fe from FeSO₄, FeEDTA, and FeEDDHA (ferric ethylenediaminedi (o-hydroxyphenylacetate)), and Mn from MnSO₄, MnEDTA, and MnEDDHA, by germinating sorghum (Sorghum vulgarie Pers. var. M 35-1) was studied. The seeds were found to absorb Fe and Mn from all the sources, and these ions moved to the scutellum, shoot, and root. EDDHA facilitated greater translocation of Fe and Mn from the seed to the shoot and root. The translocation of Fe was more towards the root than to the shoot, whereas it was the reverse in the case of Mn.     

Obligatory reduction of ferric chelates in iron uptake by soybeans

The contrasting Fe²⁺ and Fe³⁺ chelating properties of the synthetic chelators ethylenediaminedi (o-hydroxyphenylacetate) (EDDHA) and 4,7-di(4-phenylsulfonate)-1, 10-phenanthroline (bathophenanthrolinedisulfonate) (BPDS) were used to determine the valence form of Fe absorbed by soybean roots supplied with Fe³⁺-chelates. EDDHA binds Fe³⁺ strongly, but Fe²⁺ weakly; BPDS binds Fe²⁺ strongly but Fe³⁺ weakly. Addition of an excess of BPDS to nutrient solutions containing Fe³⁺-chelates inhibited soybean Fe uptake-translocation by 99+%; [Fe(II) (BPDS)₃]⁴⁻ accumulated in the nutrient solution. The addition of EDDHA caused little or no inhibition. These results were observed with topped and intact soybeans. Thus, separation and absorption of Fe from Fe³⁺-chelates appear to require reduction of Fe³⁺-chelate to Fe²⁺-chelate at the root, with Fe²⁺ being the principal form of Fe absorbed by soybean.     

Zusammenhänge zwischen der Eisenaufnahme und dem Eisentransport in der Pflanze

Zusammenfassung Junge Sonnenblumenpflanzen nahmen 8 Std. lang nicht markiertes und danach 15 Std. lang mit Fe⁵⁹ markiertes Eisen in Form von Fe-Chlorid, Fe-EDTA oder Fe-Citrat auf. 1. Bei allen drei Eisenformen absorbierten die Pflanzenwurzeln mehr Eisen aus der N?hrl?sung mit 0,1 ppm Fe als aus der mit 1,0 ppm Fe. 2. Die Wurzeln der mit Fe-Chlorid ern?hrten Pflanzen enthalten den h?chsten Gehalt an Fe⁵⁹. 3. Das Stengelexsudat der 0,1 ppm Fe-Reihe enthielt weniger Fe⁵⁹ als das Exsudat der 1,0 ppm Fe-Reihe. 4. Eine sichere Beziehung zwischen der Ern?hrung mit den verschiedenen drei Eisenformen und der ausgeschiedenen Exsudatmenge konnte nicht festgestellt werden. Ebenfalls bestand kein Zusammenhang zwischen der ausgeschiedenen Exsudatmenge und ihrem Fe⁵⁹-Gehalt. 5. Der Gehalt des Stengelexsudats an Fe⁵⁹ war bei der Ern?hrung mit Fe-EDTA und Fe-Citrat h?her als bei Fe-Chlorid.

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Relationships between iron uptake and iron transport in plants

Summary The uptake of unlabelled iron for 8 h and of Fe⁵⁹, given as Fe chloride, Fe EDTA and Fe citrate for 15 h, was investigated in young sunflower plants. 1. In all three iron forms the roots absorbed more iron from the nutrient solution with 0.1 ppm Fe than with 1.0 ppm Fe. 2. The roots of those plants, supplied with Fe-chloride contained the highest amount of Fe⁵⁹. 3. The stem exudate of plants, given a nutrient solution with 0.1 ppm Fe contained less Fe⁵⁹ than the exudate of plants, grown in a nutrient solution containing 1.0 ppm Fe. 4. No close relationship between the nutrition with the three iron forms and the produced amount of exudate could be established. Furthermore no correlation between the produced amount of exudate and its Fe⁵⁹ content could be found. 5. The content of Fe⁵⁹ in the stem exudate was higher when Fe EDTA and Fe citrate were given as compared with Fe chloride.

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Auszug aus der Dissertation des Verfassers.     

Abscisic Acid and its relationship to seed filling in soybeans

The effect of exogenous abscisic acid (ABA) on the rate of sucrose uptake by soybean (Glycine max L. Merr.) embryos was evaluated in an in vitro system. In addition, the concentrations of endogenous ABA in seeds of three soybean Plant Introduction (PI) lines, differing in seed size, were commpared to their seed growth rates. ABA (10⁻⁷ molar) stimulated in vitro sucrose uptake in soybean (cv `Clay') embryos removed from plants grown in a controlled environment chamber, but not in embryos removed from field-grown plants of the three PI lines. However, the concentration of ABA in seeds of the three field-grown PI lines correlated well with their in situ seed growth rates and in vitro [¹⁴C] sucrose uptake rates.

Across genotypes, the concentration of ABA in seeds peaked at 8.5 micrograms per gram fresh weight, corresponding to the time of most rapid seed growth rate, and declined to 1.2 micrograms per gram at physiological maturity. Seeds of the large-seeded genotype maintained an ABA concentration at least 50% greater than that of the small-seeded genotype throughout the latter half of seed filling. A higher concentration of ABA was found in seed coats and cotyledons than in embryonic axes. Seed coats of the large-seeded genotype always had a higher concentration of ABA than seed coats of the small-seeded line. It is suggested that this higher concentration of ABA in seed coats of the large-seeded genotype stimulates sucrose unloading into the seed coat apoplast and that ABA in cotyledons may enhance sucrose uptake by the cotyledons.

     

Sucrose Concentration at the Apoplastic Interface between Seed Coat and Cotyledons of Developing Soybean Seeds

The apoplastic sucrose concentration at the interface between cotyledons and surrounding seed coats of developing soybeans (Glycine max L. Merr. cv Wye) was found by three indirect methods to be in the range of 150 to 200 millimolar. This is an order of magnitude higher than has been reported elsewhere for soybean. It was also higher than the overall sucrose concentrations in the cotyledons and seed coats, each of which was approximately 90 millimolar. By defoliating plants 24 hours before measurement, both the overall sucrose concentration in the cotyledons and the interfacial apoplastic sucrose concentration were reduced by three-fourths. However, there was no day/night difference in overall tissue sucrose concentration of cotyledons or seed coats from intact plants suggesting the existence of a homeostatic mechanism compensating for the diurnal photosynthetic cycle. About 7 hours were required for a tritiated polyethylene glycol-900 solution to fully permeate developing cotyledons (from ~220 milligram fresh weight embryos), implying high diffusion resistance through the tissue.

These results indicate that a high interfacial sucrose concentration may exist in vivo. They suggest that the saturable carrier-mediated component of sucrose uptake may be of little physiological significance in the outermost cell layers of the cotyledons.

     

Physiological Characteristics of Fe Accumulation in the ;Bronze' Mutant of Pisum sativum L., cv ;Sparkle' E107 (brz brz)

The pea (Pisum sativum L.) mutant, E107 (brz, brz) accumulated extremely high concentrations of Fe in its older leaves when grown in light rooms in either defined nutrient media or potting mix, or outdoors in soil. Leaf symptoms (bronze color and necrosis) were correlated with very high Fe concentrations. When E107 plants were grown in nutrient solutions supplied 10 μm Fe, as the Fe(III)-N,N′-ethylenebis[2-(2-hydroxyphenyl)glycine] chelate, their roots released higher concentrations of Fe(III) reducing substances to the nutrient media than did roots of the normal parent cv, `Sparkle.' Reciprocal grafting experiments demonstrated that the high concentrations of Fe in the shoot was controlled by the genotype of the root. In short-term <sup>59</sup>Fe uptake studies, 15-day-old E107 seedlings exhibited higher rates of Fe absorption than did `Sparkle' seedlings under Fe-adequate growth conditions. Iron deficiency induced accelerated short-term Fe absorption rates in both mutant and normal genotypes. Iron-treated E107 roots also released larger amounts of both protons and Fe(III) reductants into their nutrient media than did iron-treated `Sparkle' roots. Furthermore, the mutant translocated proportionately more Fe to its shoot than did the parent regardless of Fe status.     

Metabolism of Gibberellin A(12) and A(12)-Aldehyde in Developing Seeds of Pisum sativum L

Metabolism of [¹⁴C]gibberellin (GA) A₁₂ (GA₁₂) and [¹⁴C]gibberellin A₁₂-aldehyde (GA₁₂-aldehyde) was examined in cotyledons and seed coats from developing seeds of pea (Pisum sativum L.). Both were metabolized to only 13-hydroxylated GAs in cotyledons but to 13-hydroxylated and non-13-hydroxylated GAs in seed coats. The metabolism of [¹⁴C]GA₁₂ was slower in seed coats than in cotyledons. [¹⁴C]GA₁₂-aldehyde was also metabolized to conjugates in seed coats. Seed coat [¹⁴C]-metabolites produced from [¹⁴C]GA₁₂-aldehyde were isolated by high-performance liquid chromatography (HPLC). Conjugates were base hydrolyzed and the free GAs reisolated by HPLC and identified by gas chromatography-mass spectrometry. [¹⁴C]GA₅₃-aldehyde, [¹⁴C]GA₁₂-aldehyde conjugate, and [¹⁴C]GA₅₃-aldehyde conjugate were major metabolites produced from [¹⁴C]GA₁₂-aldehyde by seed coats aged 20-22 days or older. The dilution of ¹⁴C in these compounds by ¹²C, as compared to the supplied [¹⁴C]GA₁₂-aldehyde, indicated that they are endogenous. Feeding [¹⁴C]GA₅₃-aldehyde led to the production of [¹⁴C]GA₅₃-aldehyde conjugate in seed coats and shoots and also to 13-hydroxylated GAs in shoots. Labeled GAs, recovered from plant tissue incubated with either [¹⁴C]GA₁₂, [¹⁴C]GA₁₂-aldehyde, or [³H]GA₉, were used as appropriate markers for the recovery of endogenous GAs from seed coats or cotyledons. These GAs were purified by HPLC and identified and quantified by gas chromatography-mass spectrometry. GA₁₅, GA₂₄, GA₉, GA₅₁, GA₅₁-catabolite, GA₂₀, GA₂₉, and GA₂₉-catabolite were detected in seed coats, whereas GA₉, GA₅₃, GA₄₄, GA₁₉, GA₂₀, and GA₂₉ were found in cotyledons. The highest GA levels were for GA₂₀ and GA₂₉ in cotyledons (783 and 912 nanograms per gram fresh weight, respectively) and for GA₂₉ and GA₂₉-catabolite in seed coats (1940 and > 1940 nanograms per gram fresh weight, respectively).     

Reduction and transport of Fe from siderophores

Soils contain siderophores produced by bacteria and fungi; however, the role of siderophores in Fe nutrition of plants is uncertain. The Strategy I plant cucumber (Cucumis sativus L.) was used in an investigation of ferric chelate reduction activity and uptake and transport of Fe from ferric hydroxyethylethylenetriacetic acid (FeHEDTA) and ferric N,N–di–(2–hydroxybenzoyl)–ethylenediamine– N,N-diacetic acid (FeHBED) and the hydroxamate siderophores, ferric rhodotorulic acid (FeRA) and ferric ferrioxime B (FeFOB). Cucumber seedlings were grown in a hydroponic medium without Fe or supplied with 10 M FeHEDTA. Iron-deficient cucumber roots readily reduced FeHEDTA, while Fe-sufficient roots had low levels of ferric chelate reduction activity. The siderophore FeRA was reduced by Fe-deficient roots at 8% of the rate of FeHEDTA, while FeFOB was not reduced. The highly stable synthetic chelate FeHBED was reduced at 16% the rate of FeHEDTA. Fe transport to shoots by Fe-deficient seedlings from the slowly reducible complexes ⁵⁹FeRA and ⁵⁹FeHBED was, respectively, 74% and 73% of that transported from ⁵⁹FeHEDTA. The ferrous complexing agent, bathophenanthrolinedisulfonic acid (BPDS), had a strong inhibitory effect on uptake and transport of Fe from ⁵⁹FeHEDTA or ⁵⁹FeRA into shoots. An average of 11% as much Fe was transported to shoots of Fe-deficient seedlings from ⁵⁹FeFOB as from ⁵⁹FeHEDTA. Neither the Fe nutritional status of the seedlings nor the presence of BPDS influenced the uptake and transport of Fe from ⁵⁹FeFOB. It is concluded that cucumber roots may take up substantial amounts of Fe from FeRA and FeHBED following reduction, while small amounts of Fe may be taken up from FeFOB by a mechanism not involving reduction of the ferric siderophore at the root surface.     

The development of isocitric lyase activity in germinating cotton seed

In cotyledons of germinating cotton (Gossypium hirsutum L. var. Stoneville 213) seedlings, in the dark, isocitric lyase (EC 4.1.3.1) activity peaks after 2 days and thereafter slowly declines to a negligible value after 8 days. The maximum activity of this enzyme in cotyledons of 2-day-old seedlings was 16.2 μmoles of glyoxylate formed/15 min·10 cotyledon pairs. Actinomycin D at a concentration of 10 μg/ml, if added to the imbibing solution, completely prevents the development of isocitric lyase activity in these germinating seed. In cotyledons of germinating cotton seedlings, in the light, isocitric lyase activity peaks after 2 to 3 days and sharply declines to a negligible value after 4 days. The maximum activity of this enzyme in cotyledons of 2- to 3-day-old seedlings was 13.2 μmoles of glyoxylate formed/15 min·10 cotyledon pairs. Actinomycin D at a concentration of 10 μg/ml, if added to the imbibing solution, severely inhibits the development of enzyme activity.     

l-Canavanine Transport and Utilization in Developing Jack Bean, Canavalia ensiformis (L.) DC. [Leguminosae

l-Canavanine, the guanidinooxy structural analog of l-arginine, is an important nonprotein amino acid of many leguminous plants with nitrogen storage a major proported role. l-[Guanidinooxy-¹⁴C]canavanine, [¹⁴C] urea, and [¹⁵N]urea were injected separately into the fleshy, green cotyledons of 9-day old jack bean plants, Canavalia ensiformis (L.) DC. [Leguminosae]. There was significant transport of canavanine from the cotyledons to the aboveground portions of the plant, but not to the roots. Within 1.5 hours of isotope administration, the remaining labeled canavanine was divided equally between the cotyledons and the aboveground portions of the plant. During the 48-hour postinjection period, the contribution of l-[guanidinooxy-¹⁴C]canavanine to the total ¹⁴carbon of the cotyledons decreased rapidly while it increased in the aboveground portions of the plant.     

Iron uptake and translocation by tomato plants as influenced by root temperature and manganese nutrition

The uptake of iron (Fe) by VF-36 tomato plants as influenced by root temperature and manganese (Mn) nutrition was studied. Following a 1-week pretreatment period of various levels of Fe and Mn in the nutrient solution in a controlled temperature room, the uptake of ⁵⁹Fe from ferric ethylenediamine di(O-hydroxyphenylacetate) (FeEDDHA) at 1 μmole per liter was studied for periods of 1 to 5 days.     

Investigation of iron pools in cucumber roots by Mössbauer spectroscopy: direct evidence for the Strategy I iron uptake mechanism

Distinct chemical species of iron were investigated by Mössbauer spectroscopy during iron uptake into cucumber roots grown in unbuffered nutrient solution with or without ⁵⁷Fe-citrate. Mössbauer spectra of iron deficient roots supplied with 10–500 μM ⁵⁷Fe-citrate for 30–180 min and 24 h and iron-sufficient ones, were recorded. The roots were analysed for Fe concentration and Fe reductase activity. The Mössbauer parameters in the case of iron-sufficient roots revealed high-spin iron(III) components suggesting the presence of Fe^III-carboxylate complexes, hydrous ferric oxides and sulfate–hydroxide containing species. No Fe^II was detected in these roots. However, iron-deficient roots supplied with 0.5 mM ⁵⁷Fe^III-citrate for 30 min contained significant amount of Fe^II in a hexaaqua complex form. This is a direct evidence for the Strategy I iron uptake mechanism. Correlation was found between the decrease in Fe reductase activity and the ratio of Fe^II–Fe^III components as the time of iron supply was increased. The data may refer to a higher iron reduction rate as compared to its uptake/reoxidation in the cytoplasm in accordance with the increased reduction rate in iron deficient Strategy I plants.     

Identification and Quantitative Analysis of Indole-3-Acetyl-l-Aspartate from Seeds of Glycine max L

Indole-3-acetyl-l-aspartate (IAAsp) was isolated from seeds of Glycine max L. cv. Hark and its identity established by its chromatographic performance and its mass spectral fragmentation. Following acid hydrolysis, the aspartate moiety was shown to be the l-enantiomer by reverse phase high performance liquid chromatographic retention time of the bisethyl ester derivatized with 2,3,4,6-tetra-O-acetyl-β-d-glycopyranosyl isothiocyanate. Isotope dilution analysis using [¹⁴C]IAAsp as internal standard showed that soybean seed contained 10 μmol/kg IAAsp and this accounted for one-half of the total indoleacetic acid of the seed.     

Effect of cadmium on iron uptake in cucumber roots: A Mössbauer-spectroscopic study

The uptake and accumulation of iron in cucumber roots exposed to cadmium were investigated with Fe sufficient and deficient cucumber plants using Mössbauer spectroscopy, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and ferric chelate reductase activity measurements. Both Fe sufficient and Fe deficient plants were applied. In the case of Fe sufficient cucumber roots grown in nutrient solution with 10 μM Cd no changes were found in the occurrence of Fe species (mostly hydrous ferric oxides and ferric-carboxylate complexes) compared to the control where no Cd was added. In the Fe deficient roots pretreated with 0, 0.1, 1, 10 and 100 μM Cd for 3 h then supplied also with 0.5 mM ⁵⁷Fe-citrate for 30 min, Fe^II was identified in a hexaaqua complex form. The relative amount of Fe^II was decreasing simultaneously with increasing Cd concentration, while the relative occurrence of Fe^III species and total Fe concentration were increasing. The results support the inhibitory effect of Cd on Fe-chelate reduction. Although the reductase activity at 10 and 100 μM Cd treatment was lower than in the iron sufficient control plants, Fe^II could be identified by Mössbauer spectroscopy whereas in the Fe sufficient control, this form was below detection limit. These data demonstrate that the influx and the reoxidation of Fe^II was decreased by Cd, consequently, they refer to the competition of Cd²⁺ and Fe²⁺ during the membrane transport and the inhibition of the reoxidation process.     

Permeability of seed coats to water as related to drying conditions and metabolism of phenolics

The seed coat of Pisum elatius is normally impermeable to water. When seeds are dried in the absence of oxygen their coats are totally permeable to water. Structural differences are observed between permeable and impermeable seed coats. In the genus Pisum, species with normally impermeable seed coats have a high content of phenolics and of catechol oxidase, while seed coats of P. sativum contain very little catechol oxidase and have a very low content of phenolics. Such differences are not noted in the cotyledons. We hypothesized that during dehydration of seeds, oxidation of phenolic compounds in seed coats through catalysis of catechol oxidase in presence of O₂ might render the seed coats impermeable to water.     

N and C NMR determination of allantoin metabolism in developing soybean cotyledons

The metabolism of allantoin by immature cotyledons of soybean (Glycine max L. cv Elf) grown in culture was investigated using solid state ¹³C and ¹⁵N nuclear magnetic resonance. All of the nitrogens of allantoin were incorporated into protein in a manner similar to that of each other and to the amide nitrogen of glutamine. The C-2 of allantoin was not incorporated into cellular material; presumably it was lost as CO₂. About 50% of the C-5 of allantoin was incorporated into cellular material as a methylene carbon; the other 50% was presumably also lost as CO₂. The ¹³C-¹⁵N bonds of [5-¹³C;1-¹⁵N] and [2-¹³C;1,3-¹⁵N]allantoin were broken prior to the incorporation of the nitrogens into protein. These data are consistent with allantoin's degradation to two molecules of urea and one two-carbon fragment. Cotyledons grown on allantoin as a source of nitrogen accumulated 21% of the nitrogen of cotyledons grown on glutamine. Only 50% of the nitrogen of the degraded allantoin was incorporated into the cotyledon as organic nitrogen; the other 50% was recovered as NH₄⁺ in the media in which the cotyledons had been grown. The latter results suggests that the lower accumulation of nitrogen by cotyledons grown on allantoin was in part due to failure to assimilate NH₄⁺ produced from allantoin. The seed coats had a higher activity of glutamine synthetase and a higher rate of allantoin degradation than cotyledons indicating that seed coats play an important role in the assimilation and degradation of allantoin.     

Fe chelates from compost microorganisms improve Fe nutrition of soybean and oat

Iron availability to plants is often limited when soil pH is 7 or higher. In C rich, but Fe limiting environments, microorganisms may produce organic chelators that complex Fe and increase its availability to plants. Seedlings of soybean (Glycine max L.) and oat (Avena sativa L.) plants, with Fe-efficient or inefficient uptake mechanisms, were grown in an Fe free nutrient solution at pH 7.5. Experiments (using a complete factorial design) were conducted in which these seedlings were transferred to a fresh nutrient solution and treated with Fe sources (FeCl₃, FeEDDHA, and Fe complexed with chelators produced by compost microorganisms (CCMs) after their enrichment in an Fe free, glucose medium), Fe concentrations (0 and 6.7 M) and antibiotic (0 and 100 mg streptomycin L^-1). Dry weight of soybean plants and Fe uptake were significantly (P 0.05) higher when Fe was supplied as ⁵⁹FeCCM than as⁵⁹ FeCl₃ and similar to when Fe was supplied as⁵⁹ FeEDDHA. Dry weight of the Fe-inefficient Tam 0-312 oat cultivar was also significantly higher when Fe was supplied as FeCCM. Fe uptake by oat, when supplied as ⁵⁹FeCCM, was twice that for⁵⁹ FeEDDHA and ⁵⁹FeCl₃. Chlorophyll concentration in plants supplied with FeCCM and FeEDDHA was significantly greater (P 0.05) than in minus Fe control plants and in FeCl₃ supplied plants. Activities of catalase and peroxidase, measured as indicators of Fe nutrition in soybean and oats, were generally increased when Fe was supplied with FeCCM as compared to the other Fe sources. The experimental conditions in which the CCMs were produced are similar to those in soil after amendment with manures or other readily available organic materials. These CCMs can bind with Fe, even under slightly alkaline conditions, and effectively improve Fe nutrition of soybean and oat.