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.     

The effects of nutrient supply,predominantly addition of iron,and rhizobial inoculation on the tolerance of Lupinus pilosus genotypes to a calcareous soil

Two glasshouse experiments were conducted to examine the effects of nutrient supply and rhizobial inoculation on the performance of Lupinus pilosus genotypes differing in tolerance to calcareous soils. In experiment 1, plants were grown for 84 days in a calcareous soil (50% CaCO₃; soil water content 90% of field capacity) at four nutrient treatments (no-added nutrients, added nutrients without Fe, added nutrients with soil applied FeEDDHA, added nutrients with foliar applied FeSO₄). In experiment 2, plants were grown for 28 days with supply of NH₄NO₃ without inoculation or inoculated with Bradyrhizobium sp. (Lupinus). Chlorosis in the youngest leaves was a good indicator of the relative tolerance of the genotypes to the calcareous soil in both experiments, except the treatment with FeEDDHA at 5 mg kg^–1 soil which was toxic to all genotypes. Chlorosis scores correlated with chlorophyll meter readings and chlorophyll concentrations. The foliar application of FeSO₄ did not fully alleviate chlorotic symptoms despite concentrations of active or total Fe in the youngest leaves being increased. Adding nutrients and chemical nitrogen did not change the severity of chlorosis or improve the growth of the plant. The nutrient supply did not alter the ranking of tolerance of genotypes to the calcareous soil. The results suggest that nutrient deficiency or poor nodulation was not a major cause of poor plant growth on calcareous soils and that bicarbonate may exert a direct effect on chlorophyll synthesis. The mechanism for tolerance is likely to be related to an ability to exclude bicarbonate or prevent its transport to the leaves.     

Leaf cuticles behave as asymmetric membranes : evidence from the measurement of diffusion potentials

Cuticles were isolated enzymatically from the leaves of two maple species (Acer saccharum Marsh and A. platanoides L.) and from orange (Citrus aurantium L.). The cuticles were placed in a plastic cuvette and different concentrations of KCl were perfused over the physiological inner and outer surfaces while the electrical potential (E¹⁰) that developed across the cuticles and was caused by ion diffusion was measured. E¹⁰ was always positive, indicating that the permeability of K⁺ was always greater than that of Cl^-. Measured E¹⁰ in cuticles did not fit the Goldman equation, whereas, E¹⁰ measured during KCl diffusion across selected artificial membranes fit the equation. The magnitude of E¹⁰ in cuticles and artificial membranes also was dependent on ionic strength, decreasing as ionic strength increased. These observations are explained by combining classical transport equations with equations that describe the equilibrium ion distribution between ionic double layers in the cuticle or membranes and the bathing solution.     

Effect of Acid treatment of plant cuticles on sorption of selected auxins

Sorption characteristics of 2-(1-naphthyl)acetic acid (NAA), 2-(1-naphthyl)acetamide (NAAm), and 2,4-dichlorophenoxyacetic acid (2,4-D) were determined for cuticles enzymically isolated from mature tomato (Lycopersicon esculentum Mill. cv Sprinter) and pepper (Capsicum annuum L.) fruit. Sorption equilibrium for NAA and 2,4-D by tomato cuticular membranes (CM) and dewaxed cuticular membranes (DCM) was achieved within 24 hours at 25°C. The average K (partition coefficient) values for NAA in tomato CM and DCM were 166 and 204, respectively, whereas the corresponding K values for 2,4-D were 292 and 383, respectively. Sorption equilibrium for 2,4-D and NAA in pepper cuticles was not achieved after 18 and 63 days, respectively. Sorption equilibrium for NAAm in tomato and pepper CM and DCM was attained within 48 hours. Acid pretreatment (2.0 n HCl, 10 minutes) had no effect on NAA, 2,4-D, or NAAm sorption by tomato CM and DCM, or on NAAm sorption by pepper CM and DCM. Acid pretreatment of pepper CM and DCM led to slightly lower K^pH (apparent partition coefficient) values for both NAA and 2,4-D. More significantly, sorption equilibrium for NAA and 2,4-D in pepper CM and DCM was achieved within 24 hours after acid treatment.     

The mode of action of fatty alcohols on leaf tissue

The mode of action of a mixture of C₈ and C₁₀ fatty alcohols, formulated in polyoxyethyelene (20) sorbitan mono-oleate (SMO) and used as an emulsion (FAE) to inhibit axillary bud (sucker) growth in tobacco production, was studied using infrared spectroscopy (NIR), photoacoustic spectroscopy (PAS), electrical resistance, and the ability of treated cells to reverse plasmolysis on leaf tissues fromNicotiana tabacum L. and other dicotyledonous species. NIR spectra showed that isolated cuticles were affected optically when treated with FAE, but did not dissolve. PAS absorbances in the UV of isolated cuticles and of epidermal peels were similar and showed that cuticles were homogeneous, unilamellar structures. In intact leaf segments, it was possible, over time using PAS absorbances in the visible region, to separate absorbance of the surface components (cuticle) from the absorption of chlorophyll and other subsurface components and to monitor the penetration by FAE into the leaf. Penetration of the FAE to the subcuticular cells took approximately 2 h. Electrical resistance measurements of FAE-treated isolated midveins of tobacco leaves decreased with time, indicating that the plasma membranes of the cells became leaky. The effect of FAE on plasma membranes of cells was confirmed withElodea sp. where leaf cells after treatment with 1 and 5% FAE lost the ability with time to plasmolyze upon exposure to a 10% solution of Ca(NO₃)₂. The results of the various studies were interpreted to mean that at the labeled concentration (4–5%) for use in the control of axillary bud growth on decapitated tobacco, FAE passed through the cuticle without disrupting it. However, the plasma membranes of the subtending cells were altered so that, in time, bud tissues desiccated (appeared burned) and growth of the sucker was controlled.     

Siderophores of Pseudomonas putida as an iron source for dicot and monocot plants

Iron uptake from ferrated (⁵⁹Fe) pseudobactin (PSB), a Pseudomonas putida siderophore, by various plant species was studied in nutrient solution culture under short term (10 h) and long term (3 weeks) conditions. In the short term experiments, ⁵⁹Fe uptake rate from ⁵⁹FePSB by dicots (peanuts, cotton and sunflower) was relatively low when compared with ⁵⁹Fe uptake rate from ⁵⁹FeEDDHA. Iron uptake rate from ⁵⁹FePSB was pH and concentration dependent, as was the Fe uptake rate from ⁵⁹FeEDDHA. The rate was about 10 times lower than that of Fe uptake from the synthetic chelate. Results were similar for long term experiments.Monocots (sorghum) in short term experiments exhibited significantly higher uptake rate of Fe from FePSB than from FeEDDHA. In long term experiments, FePSB was less efficient than FeEDDHA as an Fe source for sorghum at pH 6, but the same levels of leaf chlorophyll concentration were obtained at pH 7.3.Fe uptake rates by dicots from the siderophore and FeEDDHA were found to correlate with Fe reduction rates and reduction potentials (E₀) of both chelates. Therefore, it is suggested that the reduction mechanism governs the Fe uptake process from PSB by dicots. Further studies will be conducted to determine the role of pH in Fe aquisition from PSB by monocots.     

Cuticular penetration of abscisic acid

Summary Penetration of 2-¹⁴C abscisic acid (ABA) through enzymatically isolated cuticles from tomato fruit and from the upper epidermis of apricot, pear and orange leaves was assessed. Penetration was linear with time, greater as the undissociated than the dissociated ion, and greater through dewaxed than non-dewaxed cuticles. Significantly less (3–6 times) (2-¹⁴C)ABA penetrated the tomato fruit cuticle than NAA or 2,4-D. The leaf cuticles were less permeable than the tomato fruit cuticle. There was no evidence that the ABA was altered during transfer across the cuticle.     

Microelement composition of plants grown with low to high levels of sulfur applied to calcareous soil in a glasshouse

Summary PI54619-5-1 soybeans (Glycine max L.), which are very susceptible to Fe deficiency, were grown for 24 days in calcareous (10%) Hacienda loam soil with different levels of S each with and without 2 ppm Fe added as FeEDDHA (ferric ethylenediamine di (o-hydroxyphenylacetic acid). The S application rates ranged from sufficient to neutralize about 15% to more than all of the CaCO₃ present if the S were all oxidized. The soil pH values at harvest time ranged from 7.4 to 6.0. The highest S rate was 10% by weight of soil and it overcame Fe deficiency without FeEDDHA. The S treatments resulted in increased concentrations of Fe and other metals in leaves, but the FeEDDHA treatments increased yields more than did S. At the lower levels of S, the effects of S and FeEDDHA on Fe concentrations in leaves were additive, but not at the highest level of S. The FeEDDHA overcame much of the effect that S had on increasing Mn concentrations in leaves. It had a similar effect, particularly at the low S levels, on Zn, Cu, Al, B, and Ni concentrations in leaves. A level of S sufficient to neutralize only 15% of the CaCO₃ of the soil increased leaf concentrations of Fe, Mn, Zn, Cu, Al, B, Ni, Si, and P. The effect for Zn, Cu, and Al appreared maximum at this level. A combination of the1/2% S and the FeEDDHA resulted in the most favorable micronutrient balance. Bush beans (Phaseolus vulgaris L. var. Improved Tendergreen) grown in calcareous soil with S insufficient to neutralize all the CaCO₃ had increased Mn, Ni, and Mo and decreased Ba levels in leaves. CaSO₄ as a source of S did not have the same effects as elemental S.     

Using iron fertilizer to control Cd accumulation in rice plants: A new promising technology

Effects of two kinds of iron fertilizer, FeSO₄ and EDTA·Na₂Fe were studied on cadmium accumulation in rice plants with two rice genotypes, Zhongzao 22 and Zhongjiazao 02, with soil culture systems. The results showed that application of iron fertilizers could hardly make adverse effects on plant growth and rice grain yield. Soil application of EDTA·Na₂Fe significantly reduced the Cd accumulation in rice roots, shoots and rice grain. Cd concentration in white rice of both rice genotypes in the treatment of soil application of EDTA·Na₂Fe was much lower than 0.2 mg/kg, the maximal Cd permission concentration in cereal crop foods in State standard. However, soil application of FeSO₄ or foliar application of FeSO₄ or EDTA·Na₂Fe resulted in the significant increase of Cd accumulation in rice plants including rice grain compared with the control. The results also showed iron fertilizers increased the concentration of iron, copper and manganese element in rice grain and also affected zinc concentration in plants. It may be a new promising way to regulate Cd accumulation in rice grain in rice production through soil application of EDTA·Na₂Fe fertilizers to maintain higher content of available iron and ferrous iron in soils.     

Iron-Stress Induced Redox Activity in Tomato (Lycopersicum esculentum Mill.) Is Localized on the Plasma Membrane

Tomato plants (Lycopersicum esculentum Mill.) were grown for 21-days in a complete hydroponic nutrient solution including Fe³⁺-ethylenediamine-di(o-hydroxyphenylacetate) and subsequently switched to nutrient solution withholding Fe for 8 days to induce Fe stress. The roots of Fe-stressed plants reduced chelated Fe at rates sevenfold higher than roots of plants grown under Fe-sufficient conditions. The response in intact Fe-deficient roots was localized to root hairs, which developed on secondary roots during the period of Fe stress. Plasma membranes (PM) isolated by aqueous two-phase partitioning from tomato roots grown under Fe stress exhibited a 94% increase in rates of NADH-dependent Fe³⁺-citrate reduction compared to PM isolated from roots of Fe-sufficient plants. Optimal detection of the reductase activity required the presence of detergent indicating structural latency. In contrast, NADPH-dependent Fe³⁺-citrate reduction was not significantly different in root PM isolated from Fe-deficient versus Fe-sufficient plants and proceeded at substantially lower rates than NADH-dependent reduction. Mg²⁺-ATPase activity was increased 22% in PM from roots of Fe-deficient plants compared to PM isolated from roots of Fe-sufficient plants. The results localized the increase in Fe reductase activity in roots grown under Fe stress to the PM.     

Accumulation of cadmium and selected elements in flax seed grown on a calcareous soil

Seed of flax (Linum usitatissimum L.) grown on calcareous and neutral soils sometimes accumulates relatively high concentrations of Cd. The influence of a post-flowering application of NH₄NO₃ (115 mg N kg^-1), CdSO₄ (1 mg Cd kg^-1), FeEDDHA (2 mg Fe kg^-1), NaH₂PO₄ (120 mg P kg^-1) and ZnSO₄ (8 mg Zn kg^-1) on seed accumulation of Cd, Fe, N, Mn, P and Zn by flax grown on a Calciaquoll was studied in two experiments under greenhouse conditions. Seed yields were increased by the N and Zn treatments, and the N×Zn interaction was positive. Zinc deficiency delayed flowering and boll formation by up to 20 days and reduced seed size. In the absence of added Cd, seed accumulated up to 0.33 mg Cd kg^-1. This Cd accumulation was reduced by approximately 50 and 17% by added Zn and Fe, respectively, but was little affected by P fertilizer and post-flowering N stress. In the presence of added Cd, seed Cd exceeded 3.3 mg Cd kg^-1, and the antagonistic effects of Fe and Zn on seed Cd were absent. Seed N, P, Fe and Zn concentrations were increased on average by 10, 45, 31 and 97% by the N, P, Fe and Zn fertilizer treatments, respectively. FeEDDHA reduced seed Mn concentration by approximately 58%. However, seed Mn concentration was much less than that found in vegetative tissue at flowering. Soil-applied Zn may reduce seed Cd concentration in flax under field conditions, and may increase marketability of flax for food use.     

Using iron fertilizer to control Cd accumulation in rice plants: A new promising technology

Effects of two kinds of iron fertilizer, FeSO4 and EDTA·Na2Fe were studied on cadmium accumulation in rice plants with two rice genotypes, Zhongzao 22 and Zhongjiazao 02, with soil culture systems. The results showed that application of iron fertilizers could hardly make adverse effects on plant growth and rice grain yield. Soil application of EDTA·Na2Fe significantly reduced the Cd accumulation in rice roots, shoots and rice grain. Cd concentration in white rice of both rice genotypes in the treatment of soil application of EDTA·Na2Fe was much lower than 0.2 mg/kg, the maximal Cd permission concentra- tion in cereal crop foods in State standard. However, soil application of FeSO4 or foliar application of FeSO4 or EDTA·Na2Fe resulted in the significant increase of Cd accumulation in rice plants including rice grain compared with the control. The results also showed iron fertilizers increased the concentra- tion of iron, copper and manganese element in rice grain and also affected zinc concentration in plants. It may be a new promising way to regulate Cd accumulation in rice grain in rice production through soil application of EDTA·Na2Fe fertilizers to maintain higher content of available iron and ferrous iron in soils.     

Accumulation and within-seed distribution of iron in common bean and soybean

The influence of times of applying FeEDDHA on seed yield and Fe accumulation by four common bean (Phaseolus vulgaris L.) and two soybean (Glycine max L.) genotypes grown on a calcareous soil was studied under greenhouse conditions. The soybean genotypes, unlike the common bean genotypes, developed Fe-deficiency chlorosis and responded to application of the chelate. A preplant application of FeEDDHA was more efficacious than a flowering application in increasing seed yield of soybean. In contrast, the flowering application was much more effective than the preplant application for increasing seed Fe concentration [Fe] of both species. Percentage of seed Fe located in the seed coat of the common bean genotypes ranged from approximately 5 to 40% and was little affected by FeEDDHA. This within-seed distribution of Fe was correlated with methanol-extractable seed-coat pigments absorbing at 500 nm, presumably anthocyanins, but not with condensed tannins (proanthocyanidins). The soybean genotypes did not accumulate anthocyanins or tannins in the seed coat. Seed of Fe-deficient soybean plants without FeEDDHA had appreciably lower [Fe] and had a lower percentage of seed Fe in the seed coat than treated plants. Within-seed distribution of Fe should be considered in plant breeding because of concerns about both human nutrition and early seedling growth. Abbreviations: DTPA – diethylenetrinitrilopentaacetic acid; EDDHA – ethylenediamine di(o-hydroxyphenylacetic acid) acid; SPAD – single photon avalanche diode     

Cation Penetration through Isolated Leaf Cuticles

The rates of penetration of various cations through isolated apricot Prunus armeniaca L. leaf cuticles were determined. Steady state rates were measured by using a specially constructed flow-through diffusion cell. The penetration rates of the monovalent cations in group IA followed a normal lyotropic series, i.e., CS⁺ ≥ Rb⁺ > K⁺ > Na⁺ > Li⁺. The divalent cations all penetrated through the cuticle more slowly than the monovalent cations. Comparison of the relative values of k (permeability coefficient) and D (diffusion coefficient) indicates that the penetration of ions through isolated cuticles took place by diffusion and was impeded by charge interactions between the solute and charge sites in the penetration pathway. Cuticular penetration rates of K⁺ and H₂O at pH above 9 were of similar magnitude. At pH 5.5 H₂O penetration was not affected but that of K⁺ was greatly reduced. From this observation and from data on cuticle titration and ion adsorption studies, we hypothesize that cuticular pores are lined with a substance (perhaps a protein) which has exposed positively charged sites.     

The effect of iron ethylenediaminetetraacetic acid on the growth and metabolism of tomato plants in water culture

Summary Tomato plants were grown in nutrient culture either continuously or discontinuously treated with FeSO₄ or with Fe-EDTA. FeSO₄ rapidly gave a precipitate of Fe₂O₃.nH₂O but remained, under the conditions of the experiments, available to the plants. Fe absorbed from Fe-EDTA in the nutrient medium was less effective in inducing tomato plant growth than iron supplied as ferrous sulphate. This cannot be explained in terms of luxury consumption or by phosphate-induced internal iron immobilization.Plants grown continuously with Fe-EDTA as an iron source showed consistently higher peroxidase and catalase activities. Chlorotic plants treated for a few days with FeSO₄ exhibited mostly equal or higher enzyme activities than those treated with Fe-EDTA. The ratio of green and yellow chloroplast pigments was constant under all the tested levels of iron nutrition.Although there were significant differences in iron utilization, enzyme activities, and some symptoms of slightly modified growth, the main conclusion of this investigation is that, under these strictly comparable conditions, plant metabolism has not been modified considerably by the use of the synthetic iron chelates.     

FeEDDHA-facilitated Fe uptake in relation to the behaviour of FeEDDHA components in the soil-plant system as a function of time and dosage

FeEDDHA products are widely used to prevent and remedy Fe chlorosis in crops grown on calcareous soils. These products consist of a mixture of FeEDDHA components: racemic o,o-FeEDDHA, meso o,o-FeEDDHA, o,p-FeEDDHA and rest-FeEDDHA. The FeEDDHA components differ in physical and chemical properties, and as a consequence also in effectiveness as Fe fertilizer. In order to efficiently match dose, frequency and moment of FeEDDHA application with the Fe requirements of plants, it is important to understand the behaviour of the FeEDDHA components in the soil-plant system as a function of time and dosage, and to relate this behaviour to Fe uptake by plants. These issues have been examined in a pot trial study with soybean plants (Glycine max (L.) Merr. cv Mycogen 5072) grown on calcareous soil from Santomera, Spain. Four FeEDDHA treatments (two compositions, two dosages) were applied prior to the set in of chlorosis. Leaching of FeEDDHA components was prevented. Plant and soil were sampled every week, for six weeks. From one week onward the Fe concentration in the pore water was largely gouverned by racemic and meso o,o-FeEDDHA. The concentration behaviour of the o,o-FeEDDHA isomers underwent two stages: a strong decline within the first week resulting from linear adsorption, and a gradual decline from one week onward. For meso o,o-FeEDDHA, unlike racemic o,o-FeDDHA, the gradual decline could be mathematically well described with an exponential decay function. Soybean plants mainly took up Fe in the progressed vegetative stage (3rd and 4th week) and in the reproductive stage, when the pods were being filled with seeds (6th week). Fe uptake and removal of racemic o,o-FeEDDHA from the soil system display a similar time-trend, whereas the removal of meso o,o-FeEDDHA had a plant-independent character. This indicates the removal of racemic o,o-FeEDDHA is to a larger extent plant-related.     

Iron induction of lipid peroxidation and effects on antioxidative enzyme activities in rice leaves

Lipid peroxidation in relation to toxicity of detached rice leavescaused by excess iron (FeSO₄) was investigated. ExcessFeSO₄, which was observed to induce toxicity, enhanced the contentoflipid peroxidation but not the content of H₂O₂.Superoxidedismutase activity was reduced by excess FeSO₄. Ascorbate peroxidaseand glutathione reductase activities were increased by excess FeSO₄.Free radical scavengers, such as mannitol and reduced glutathione, inhibitedexcess iron-induced toxicity and at the same time inhibited excessiron-enhancedlipid peroxidation, suggesting that lipid peroxidation enhanced by excess ironis mediated through free radicals.     

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.     

Effect of iron on activity of soybean multi-subunit acetyl-coenzyme A carboxylase

Multi‐subunit acetyl‐coenzyme A carboxylase (MS‐ACCase; EC 6.4.1.2) isolated from soybean chloroplasts is a labile enzyme that loses activity during purification. We found that incubating the chloroplast stromal fraction under anaerobic conditions or in the presence of 5 mM FeSO₄ stimulated ACCase (acetyl‐CoA→malonyl‐CoA) and carboxyltransferase (malonyl‐CoA→acetyl‐CoA) activity. Fe‐stimulation of activity was associated with ⁵⁹Fe binding to a stromal protein fraction. ACCase and carboxyltransferase activities measured in the stromal protein fraction containing bound ⁵⁹Fe were 2‐fold and 6‐fold greater, respectively, than the control (stromal fraction not pretreated with FeSO₄). Superose 6 gel filtration chromatography indicated ⁵⁹Fe comigrated with stromal protein of approximately 180 kDa that exhibited carboxyltransferase activity, but lacked ACCase activity. Anion exchange (Mono‐Q) chromatography of the Superose 6 fraction yielded a protein peak that was enriched in carboxyltransferase activity and contained protein‐bound ⁵⁹Fe. Denaturing gels of the Mono‐Q fraction indicated that the 180‐kDa protein was composed of a 56‐kDa subunit that was bound by an antibody raised against a synthetic β‐carboxyltransferase (β‐CTase) peptide. Incubation of the Mono‐Q carboxyltransferase fraction with increasing concentrations of iron at a fixed substrate concentration resulted in increased initial velocities that fit well to a single rectangular three parameter hyperbola (v=v_o+V_max[FeSO₄]/K_m+[FeSO₄]) consistent with iron functioning as a bound activator of catalysis. UV/Vis spectroscopy of the partially purified fraction before and after iron incubation yielded spectra consistent with a protein‐bound metal cluster. These results suggest that the β‐CTase subunit of MS‐ACCase in soybean chloroplasts is an iron‐containing enzyme, which may in part explain its labile nature.