Soybean response to iron‐deficiency stress as related to iron supply in the growth medium

The Fe‐inefficient T203 and the Fe‐efficient A7 and Pioneer 1082 (P1082) soybeans (Glycine max (L.) Merr.) were grown hydroponically with no (0 mg Fe L^‐1 ; ‐Fe) and a minute level (0.025 mg Fe L^‐1 ; +Fe) of Fe to (a) compare their responses to Fe‐deficiency stress and (b) relate Fe‐efficiency in soybeans to their ability to initiate the Fe‐stress‐response mechanism at low levels of Fe. With no Fe in solution, P1082 released similar levels of H⁺ ions, but released less reductant from their roots and there was less reduction of Fe³⁺ to Fe²⁺ by their roots than by A7 roots. These responses were also one day later and occurred after a more severe chlorosis and a lower leaf Fe had developed in P1082 than in A7. With 0.025 mg L^‐1 of solution Fe, it was not necessary for the Fe‐stress response mechanism to be fully activated to make Fe available in A7 soybean, whereas a strongly enhanced Fe stress response was observed in P1082. Increased Fe uptake and regreening of leaves immediately succeeded initiation of the Fe stress response in both cultivars and at both levels of Fe. Thus, P1082 was slightly less efficient than A7 soybean, but would be classed more efficient than the previously studied soybean cultivars A2, Hawkeye, Bragg, Pride, Anoka, and T203. These results support the hypothesis that the most efficient soybeans are those which can initiate the Fe‐stress response mechanism with little or no Fe in the growth medium. The near simultaneous occurrence of the factors in the Fe‐stress response mechanism (H ion and reductant release, reduction of Fe to Fe by roots), and the immediate increase in leaf Fe and chorophyll contents following that response suggest that all these factors act in concert, not independently, to aid in the absorption and transport of Fe to plant tops.     

Root responses of sterile‐grown onion plants to iron deficiency 1

Onion (Allium sativum) plants grown without iron (Fe) in sterile nutrient solutions readily developed chlorosis symptoms. Iron deficiency in the sterile‐grown plants stimulated the rates of root extracellular reduction of Fe³⁺, copper (Cu²⁺), manganese (Mn⁴⁺), and other artificial electron acceptors. While rapid reduction occurred with the synthetic chelate Fe³⁺HEDTA, no short‐term reduction occurred with the fungal siderophore Fe³⁺ferrioxamine B (FeFOB). In addition to the increased rate of extracellular electron transfer at the root surfaces, the Fe‐deficient plants showed greater rates of Fe uptake and translocation than the onion plants grown with Fe. The rates of uptake and translocation of Fe were sharply higher for the Fe‐deficient plants supplied with FeHEDTA than for similar plants supplied with FeFOB. Inhibition by BPDS of the Fe uptake by the Fe‐deficient onion plants further supported the importance of Fe³⁺ chelate reduction for the uptake of Fe into the roots. Rates of Fe uptake and translocation by Fe‐deficient onion plants supplied with ⁵⁵FeFOB were identical to the rates of uptake of ferrated [14C]‐FOD; a result that gives evidence of the uptake and translocation of the intact ferrated siderophore, presumably by a mechanism not involving prior extracellular Fe³⁺ reduction. Differences in the rates of transport of other micronutrients into the roots of the Fe‐deficient onion plants were evident by the significantly higher Zn and Mn levels in the shoots of the Fe‐deficient onion.     

Distribution pattern of root‐supplied 59iron in iron‐sufficient and iron‐deficient bean plants

In order to study the iron (Fe) distribution pattern in bean plants with different Fe nutritional status, french bean (Phaseolus vulgaris L.) seedlings were precultured in a complete nutrient solution with 8x10^‐5 M FeEDTA for five days. Thereafter, plants were further supplied with 8x10^‐5 M FeEDTA (Fe‐sufficient) or with only 2x10^‐6 M FeEDTA (Fe‐deficient) for another eight days. At this stage, the Fe‐deficient plants had much lower chlorophyll contents and lower dry weight of the leaves but higher reducing capacity of the roots compared with the Fe‐sufficient plants. For studies on short‐term distribution of Fe, the Fe‐sufficient plants were supplied 8x10^‐5 M ⁵⁹FeEDTA (specific activity 9.9 GBq/mol) and the Fe‐deficient plants 1x10⁶ M ⁵⁹FeEDTA (specific activity 98.8 GBq/mol). The plants were harvested after 4 and 24 hours. Despite a much lower supply of ⁵⁹FeEDTA/(factor 80), the Fe‐deficient plants took up significantly more ⁵⁹Fe but translocated less to the shoots (14.6% after 24 h) compared with the Fe‐sufficient plants (29.4% after 24 h). However, regardless of the Fe nutritional status of the plants, the majority of ⁵⁹Fe was translocated in the primary leaves. Our results demonstrate a similar distribution patterns of root‐derived ⁵⁹Fe in the shoots of Fe‐sufficient and Fe‐deficient plants, and thus, no preferential direct translocation of Fe to the shoot apex in the Fe‐deficient plants.     

Nitric acid‐ and o‐phenanthroline‐extractable iron for diagnosis of iron chlorosis in citrus lemon trees

Abstract

Plant analysis for total iron (Fe) is frequency used for diagnosis of Fe‐deficiency chlorosis. However, chlorotic plants frequency contained similar or higher amount of total Fe than the healthy green plants. The objectives of this study were to (i) determine if Fe chlorosis in citrus lemon can be diagnosed by total or active Fe and can be related to the degree of chlorosis, and (ii) determine the optimum extraction time and ratio of extracting solution to plant sample for extracting the active Fe. Leaf samples of different degrees of Fe chlorosis were sampled from different citrus lemon trees from three different sites. Total Fe was extracted with nitric acid (HNO₃) and active Fe with o‐phenanthroline from lemon leaves. An extraction time of 20 and 45 hours and the ratios of the extractor to the sample of 5:l, 10:1, and 20:1 were investigated. The results indicated that an extraction time of 20 hours is enough for extracting the active Fe from citrus lemon leaves by o‐phenanthroline. The amount extracted by all ratios (5:1, 10:1, and 20:1) were detectable and at the same time similarly and consistency showed the differences in degrees of chlorosis in all plant samples. Total Fe content was always higher in moderately and severely chlorotic leaves compared to the green leaves and was not related to the degree of chlorosis. Therefore, total Fe cannot be used as a criteria to differentiate between the Fe‐deficient and non‐deficient plants. On the other hand, active Fe tended to decrease with the increase in the degree of chlorosis. The ratio of active to total Fe was calculated and was found to be closely correlated with the degree of chlorosis. This clearly illustrates the failure of plant analysis for total Fe and the effectiveness of active Fe and/or the ratio of active to total Fe for diagnosing Fe chlorosis.     

Use of 1,10‐phenanthroline in estimating metabolically active iron in plants

Abstract

If calcifuges are forced to grow on a calcareous soil, they usually develop chlorosis. However, total leaf iron (Fe) does not often correlate well with Fe deficiency symptoms. The extraction of ‘active’ Fe by 1 M HCl or Fe chelators, e.g., 1,10‐phenanthroline, may reflect the relation between chlorosis and Fe‐concentration in the leaves better than total Fe does. Extraction of ‘active’ Fe from leaves of wild plants by 1,10‐phenanthroline, citric acid and HC1 was compared. The 1,10‐phenanthroline was chosen for further methodological studies. All samples were extracted at indoor light conditions and analyzed by AAS because dark incubation did not influence the oxidation state of Fe and non‐specific light absorbance seemed to be high in colorimetric analysis. Washing of leaf material with H₂O seemed to clean the leaf surfaces equally well as with 0.1 M HCl. Only fresh leaf material was extracted, as pretreatment (freezing or drying) changed the extractability of Fe. An extraction time of 16 h was adequate for the herbaceous plants tested but not for Carex pilulifera, where extracted Fe increased linearly with time. The age of the extractant solution may play a role because 1,10‐phenanthroline had lost part of its chelation capacity after 6 weeks. The ratio of leaf weight:extractant volume did not influence the amount of Fe extracted, provided the same amount of chelator was supplied. The 1,10‐phenanthroline did not interfere with the Fe determination by AAS, and HCl pH 3 as used for the preparation of the extractants had only a marginal influence on Fe extractability compared to 1,10‐phenanthroline at pH 3. To get comparable results the extraction method should be standardized as much as possible. Samples can be stored in the refrigerator for several hours before adding the extractant and the extracts can be stored for a few days or frozen and measured on the same day, with the same instrument setting.     

On‐farm diagnosis and management of iron chlorosis in groundnut

Abstract

Iron (Fe) chlorosis is a major nutritional constraint to groundnut (Arachis hypogaea L.) productivity in many parts of the world. On‐farm research was conducted at a Fe‐chlorotic site to evaluate the performance of three genotypes (TMV‐2, ICGS‐11, and ICGV‐86031), three fertilizer practices [no fertilizer control, fanners practice (125: 200: 0 kg NPK ha^?1), recommended practice (20: 50: 30 kg NPK ha^?1)], and two Fe treatments (non‐sprayed control and foliar FeSO₄ sprays) for their effect on Fe‐chlorosis and haulm and pod yields. These treatments were tested in a strip‐split plot design with four replicates. Results revealed that TMV‐2 and ICGS‐11 were susceptible to Fe‐chlorosis and produced significantly smaller haulm and pod yield, whereas, ICGV‐8603 1 was tolerant to Fe‐chlorosis. Farmer's fertilizer practice had the highest incidence of Fe‐chlorosis. Extractable Fe and chlorophyll content in the fresh leaves were the best indices of Fe‐status and were significantly (P<0.01) correlated with visual chlorosis ratings. Foliar application of FeSO₄ (0.5 w/ v) was effective in correcting Fe‐chlorosis and increased pod yield by about 30 to 40% in susceptible genotypes. These results suggests that use of tolerant genotypes such as ICGV‐86031 or foliar application of FeSO₄ in susceptible genotypes such as TMV‐2 and ICGS‐11 in combination with recommended fertilizer levels is an effective management package for alleviating Fe‐chlorosis in groundnut.     

Energy dispersive X‐ray fluorescence for rapid potassium,calcium, and chloride diagnosis in barley

Barley (Hordeum vulgare L. cv Doriru) leaf samples were collected from a field comprising three plots, plot F chemical fertilizer treated, plot S receiving sewage sludge and sawdust mixed compost, and plot H receiving sewage sludge and rice husk mixed compost. Relative concentrations of selected elements, potassium (K), calcium (Ca), and chloride (Cl) of young, mature, and old barley leaves were determined by microscopic energy dispersing X‐ray fluorescence (EDXRF). The objective of this investigation was to verify the applicability of EDXRF for rapid nutrient element diagnosis of plants. Typically whole leaves were washed in deionized‐distilled water and dried by ironing for analysis. Intact dried barley leaf sample irradiation was accomplished with X‐rays obtained from an X‐ray tube focused on an area <100 μm of the respective sample specimen surface. The EDXRF provided sufficient sensitivity for relative concentrations of K, Ca, and Cl. Element content data of all the elements investigated, specifically K, resulted in adequate plant nutrient element values to diagnose K insufficiency in barley leaves taken from plants in the sewage sludge receiving plots. Potassium was more densely accumulated in the new leaf than in mature and old leaves in case of plants from the S and H plots. In contrast, such K accumulation was more dense in old and mature leaves than young leaves in case of plants from the F plot. However, Cl and Ca coupling in barley leaves from all of the F, S, and H plots had shown the similar pattern of distribution and followed the order: old > mature > young. Therefore, EDXRF can be an easy, rapid, and practical method for diagnosing the elemental content of plant tissues and thereby help to aid plant growth and development through timely supplements of the required element(s).     

Behavior of iron‐inefficient plants when grown in combinations of calcareous and noncalcareous soils

Abstract

When Fe‐inefficient plants were grown in mixtures of calcareous Hacienda loam soil and noncalcareous Yolo loam soil compared with plants grown in unmixed soils, characteristics and composition of the plants including Fe deficiency were generally intermediate to those with either soil alone. Noncalcareous soil adjacent to calcareous soil allowed PI 54619–5–1 soybeans (Glycine max L.) to obtain sufficient Fe.     

Differential expression of iron deficiency‐induced genes in barley genotypes with differing manganese efficiency

The expression of two barley genes, Ids1 and Ids2, that were induced specifically by iron (Fe) deficiency stress in solution culture, was examined in two barley genotypes differing in manganese (Mn) efficiency. Plants were grown in a calcareous soil supplied with two levels of Mn (15 and 100 mg/kg soil). Ids1 was expressed at equal levels in the roots of both genotypes, and this expression was not affected by Mn supply. These results suggest that the expression of Ids1 probably does not contribute to Mn efficiency. A contrasting result was obtained for Ids2, which was expressed at a higher level in the roots of the Mn‐inefficient genotype than in the Mn‐efficient genotype. However, the expression levels also were not affected by Mn supply. The differential expression of Ids2 may indicate that this gene plays a role both in the Fe deficiency response and in the Mn efficiency mechanism. An interesting observation made on the time course of expression of the two genes. Initially, both genes had low expression in two week old plants and then much higher expression in three week old plants. The timing of this increase probably relates to the exhaustion of the seed Fe reserves. Therefore, our results indicate a need to consider the effect of seed nutrient content in research on the molecular basis for micronutrient acquisition.     

Pattern of iron distribution in the soil‐plant system and its possible relation to iron‐chlorosis

Abstract

The frequent concentration‐ranges of various nutrient elements in soils and in plants are compared. Iron is different from almost all other nutrient elements in the fact that its optimal concentration range in plants is much lower than its frequent concentration range in soils. It is suggested that this observation is related to a chemical‐physiological mechanism of control on the uptake of iron by plants which in turn may explain the situations in which iron deficiency conditions in plants arise.     

Use of basic salts of iron and zinc as plant amend‐ments in soils

Abstract

In a greenhouse experiment, the effects of adding zinc (Zn) and iron (Fe) as either their basic salts or as commercial chelates were compared for the production of lettuce. The basic salts were found to be as effective as the chelates in providing Zn and Fe as well as being more environmentally safe.     

Factors in iron‐stress response mechanism enhanced by Zn‐deficiency stress in Sanilac,but not Saginaw navy bean

Zinc‐inefficient Sanilac and Zn‐efficient Saginaw navy bean (Phaseolus vulgaris L.) differ in their susceptibility to Zn‐deficiency stress. Sanilac accumulates Fe under Zn‐deficiency stress and Saginaw does not. These two navy bean cultivars were grown at 0, 0.006 and 0.12 mg/L Zn in modified Hoagland nutrient solution. Various Fe‐stress response mechanisms were quantified periodically over a 12‐day experimental period to determine if known factors in the Fe‐stress response mechanism were enhanced by Zn‐deficiency stress. Visual Zn‐deficiency symptoms were more severe in Sanilac than Saginaw navy bean under equivalent Zn treatments. Sanilac contained lower leaf Zn than Saginaw when Zn was present in solution (0.006 and 0.12 mg/L Zn), but the two cultivars were similar in leaf Zn in the absence of Zn (0 mg/L Zn). Sanilac accumulated more leaf Fe than Saginaw when under Zn stress (0 and 0.006 mg/L Zn). The higher levels of leaf Fe in Sanilac than Saginaw were closely associated with enhanced release of reductants and increased reduction of Fe³⁺ to Fe²⁺ by roots of Sanilac. Saginaw navy bean roots reduced Fe³⁺ to Fe²⁺ similarly to Sanilac with adequate Zn present in solution (0.12 mg/L), but experienced minuscule levels of Fe³⁺ reduction under Zn deficiency. Zinc deficiency stimulated the initiation of the Fe‐stress response mechanism in Sanilac, but not Saginaw, which may have enhanced the development of Zn‐deficiency symptoms in Sanilac due to the increased uptake of Fe by this cultivar. The common Fe‐deficiency stress response associated primarily with grasses (release of phytosiderophore) was not found in either navy bean cultivar.     

Iron‐Enriched Azolla as a slow‐release biofertilizer for cucumber plants grown in a hydroponic system

The unique ability of dried plant residues Azolla to adsorb iron (Fe) was employed to formulate and test an organic Fe biofertilizer. A simplified experimental system was established to examine the effectiveness of Fe‐enriched Azolla as a source of Fe for the remedy of Fe‐deficient plants. The optimal Fe‐enrichment level needed to achieve a complete recovery of starved plant by the Fe‐Azolla complex was tested using a bioassay system of hydroponically grown cucumbers. Dried Azolla plants were mixed a with a solution of ferrous sulfate (FeSO₄) at pH 2.0, rinsed, and dried to form organic, compact material containing 4% (w/w) Fe bound to Azolla. The Fe‐Azolla complex was applied to the nutrient solutions of Fe‐deficient cucumber seedlings. Growth rates and development measurements as well as chlorophyll and the Fe‐containing catalase activity tests have been performed. The effect of the slowly released Fe in correcting Fe deficiency were followed for three weeks and compared with the efficiency of additions of several synthetic Fe chelates. Iron‐starved plants exhibited fast regreening of the chlorotic interveinal tissues after the addition of Fe‐Azolla complex to the nutrient solutions. Iron starvation decreased the activity of catalase. Iron‐treated‐starved plants exhibited recovery of catalase activity compared to the low level activity measured untreated Fe‐starved plants. Iron‐enriched Azolla treatment was found equivalent to Fe‐EDTA and Fe‐EDDHA. This study is the first step in our research program aimed to establish the application of Fe‐enriched Azolla as a bioagent for the benefit of Fe‐deficient crops.     

Participation of silicon in cation‐anion balance as a possible mechanism for aluminum and iron tolerance in some gramineae

Abstract

Silicon (Si) has been suggested as a factor in aluminum (Al) tolerance of some species of the gramineae when grown on acid soils. Silicon concentrations are generally much higher in monocot plants than in dicot plants, and the phenomenon is related to the fact that mineral cation:mineral anion uptake ratio is much higher in dicots than in monocots. When large amounts of anionic Si, supposedly as sulfate (SO₄ ^4‐), participate in cation‐anion balance to add to the excess of anion uptake, equivalent amounts of hydroxyl ions should be expelled from roots which can increase rhizosphere pH and decrease uptake of Al and iron (Fe). The magnitude of OH^? released by roots for a 5000 kg/ha crop with an excess uptake of 1% Si can be equivalent to 357 kg lime per hectare. This could be very significant in decreasing Al and Fe uptake from acid soils when localized in the rhizosphere. Success of agriculture on highly acid soils may be enhanced by use in a rotation of crops and cultivars that have the ability to accumulate Si.     

Modified procedures for commercial adaptation of root iron‐reducing capacity as a screening technique

Abstract

Genotypic evaluation is critical to development of soybean [Glycine max (L.) Merr.] cultivars with genetic resistance to Fe‐deficiency chlorosis. Root Fe³⁺ reducing activity is correlated with genotypic resistance to Fe chlorosis measured in field nurseries, and thus may be a reliable method for identifying chlorosis‐resistat genotypes. However, to develop methods useful for large‐scale screening, several modifications of the previously published procedure for measuring root Fe³⁺ reducing activity were investigated. Several hydroponic experiments were conducted to test proposed modifications. It was determined that: (a) different genotypes may be grown together in the same nutrient solution without affecting Fe³⁺ reduction, (b) genotype separation is maximized by growth in CaCO₃ buffered solution (37.5 mg L^?1), (c) a labor‐intensive elongation step can be eliminated, and (d) denotype evaluation can be accomplished without introducing Fe into the hydroponic solutions. These refinements to the procedure should allow its adaptation and use in soybean breeding programs.     

Use of a radio‐labelled chloric anion (36CLO3‐) as an analogue for tracking the nitrate (NO3‐) transport in higher plants

The suitability of the use of radio‐labelled chloric (³⁶ClO₃‐) as an analogue for tracing nitrate (NO₃ ^‐) uptake by intact plants was examined with regards to the possibly promising properties of the radioisotope for application in microautoradiographic studies. The identity of the electrolytically produced ³⁶ClO₃ ^‐ was checked by TLC autoradiography and radio high pressure liquid chromatography (HPLC). The experiments were carried out at the lower concentration range of NO₃‐ uptake with different plant species using double labelling with ³⁶ClO₃‐ and ¹³NO₃‐. The results demonstrate that the influx as well as the release from the labelled root system to exchange solutions differed markedly between the two tracers indicating a strong discrimination between ClO₃‐ and NO₃‐ ions. Thus, ³⁶ClO₃‐ labelling was considered to be inadequate for following the pathway of NO₃‐ across the root tissue by microautoradiographic methods.     

Effects of Dibutyl phthalate and phthalic acid on chlorosis recovery in iron‐deficiency stressed sorghum cultivars

The effects of DBP (Dibutyl phthalate) and PA (Phthalic acid) supplied to the nutrient medium of Fe‐deficiency stressed sorghum cultivars, CSH‐5, 2077‐A, and CS‐3541 were examined. It was found that both the chemicals (50 mg/1) caused recovery of the cultivars CSH‐5 and 2077‐A in 4 days of treatment. Furthermore, the growth of roots, especially the adventitious roots, was increased by the chemicals.     

Simplified procedure for rapid,manual analysis of nitrate in soil extracts by copper‐cadmium reduction

Abstract

An inexpensive modification of the commonly used manual nitrate (NO₃)‐nitrogen (N) analysis for soil extracts is described. This procedure uses multiple reductors of copperized cadmium (Cd) wire threaded through Teflon tubing and a peristaltic pump to rapidly pass a low volume of soil extract through the reductors at a constant flow rate. In excess of 150 prepared samples can be processed daily with minimum waste generation. Efficiency of reduction is >98% and precision of analysis (coefficient of variation) for replicate standards of known NO₃‐N concentration is excellent, at <0.5% over the concentration range 0.025 to 0.2 μg NO₃‐N mL^‐1. Column life and storage characteristics are high, at >250 samples per column and one month, respectively. Column activation and regeneration in these wire type reductors are simpler and less tedious than for reductors constructed of copperized Cd granules.     

The content of microelements and iron in soils and plants in the basin of lake Kotokel’ in Western Transbaikalia

The content of microelements (Mn, Zn, Cu, Co, Ni, Cr, Pb, and Cd) and Fe is determined in the soils and plants of the Lake Kotokel’ basin. Their content in the soils is proved not to exceed the regional background and the existing MPC and APC. The content of Cd is revealed to exceed its clarke value for the world soils, which is related to the natural origin of this element. The concentrations of Mn, Co, and Pb are close to their clarke values, and those of Zn, Cu, Ni, and Cr are lower than their clarkes. The studied soils are specified by the maximal amount of the mobile forms of microelements. The profile distribution of the microelements differs depending on the genetic soil type. For Mn, Zn, and Cu, a significant biogenic accumulation is pronounced in the organic soil horizons. The content of microelements in the aboveground phytomass exceeds the maximal permissible levels for Mn, Co, Cr, and Fe. The intensity of the microelements absorption by the plants varies widely, being specified by the high coefficient of the biological adsorption (except for Fe). Mn, Zn, and Cu are accumulated in the plant phytomass the most intensely.     

Application of capillary electrophoresis on the characterization of cadmium‐induced polypeptides in roots of pea plants

Capillary electrophoresis (CE) has revealed as a powerful technique for a rapid and effective evaluation of the synthesis of polypeptides induced by cadmium (Cd) in root tissues of Cd‐resistant pea plant. CE was performed on root extracts in capillary gel electrophoresis (CGE) using 3% PEG 2November 1998 in Tris‐Tricine buffer as a dynamic sieving polymer solution and in free solution (FSCE) with 0.1M Tris‐Tricine at pH 8.3 as running buffer. By comparison with control, CGE electropherograms of root extracts of Cd‐resistantpea showed a new peak, characteristic of newly synthesized polypeptidic fraction with apparent molecular weight of 10 kDa. In order to get more information, we characterized further the new synthesized polypeptidic fraction as charge to size ratios. Results obtained by FSCE in free solutions showed that polypeptidic fraction split into several components with different charge to size ratios, very close to that of glutathione, the starting molecule for the biosynthesis of phytochelatins. In addition, results suggested a co‐occurrence of MT‐like proteins at low molecular weight and phytochelatins.