Chromium III‐iron interaction in iron sufficient and iron deficient bean plants. II. Ultrastructural aspects

The influence of a growth stimulating low Cr III concentration (1.0 μM) on chloroplast ultrastructure, the Fe, Cr, and Mn content of chloroplast extracts, o‐phenantroline extractable leaf Fe, and catalase activity was studied in both Fe‐sufficient and Fe‐deficient bush bean (Phaseolus vulgaris L.) plants. Chromium supply hardly affected the chloroplast ultrastructure of Fe‐sufficient plants but significantly improved chloroplast ultrastructure in Fe‐deficient leaves. Generally, Cr supply did not significantly influence chloroplast Fe‐content, but increased the Fe/Mn ratio in Fe‐deficient chloroplasts. In leaves from Fe‐deficient plants, o‐phenantroline extractable Fe was significantly increased, while catalase activity was not significantly influenced by Cr supply. The possible mechanisms of the beneficial effects of Cr III in Fe‐deficient plants are discussed.     

Arsenic–iron interaction: Effect of additional iron on arsenic-induced chlorosis in barley grown in water culture

Abstract

The effect of additional iron (Fe) on arsenic (As) induced chlorosis in barley (Hordeum vulgare L. cv. Minorimugi) was investigated. The treatments were: (1) 0?μmol?L^?1 As?+?10?μmol?L^?1 Fe³⁺ (control), (2) 33.5?μmol?L^?1 As?+?10?μmol?L^?1 Fe³⁺ (As-treated) and (3) 33.5?μmol?L^?1 As?+?50?μmol?L^?1 Fe³⁺ (additional-Fe³⁺) for 14?days. Arsenic and Fe³⁺ were added as sodium-meta arsenite (NaAsO₂) and ethylenediaminetetraacetic acid-Fe³⁺, respectively. Chlorosis in fully developed young leaves was observed in the As-treated plants. The chlorophyll index and the Fe concentration decreased in shoots of the As-treated plants compared with the control plants. Arsenic reduced the concentration of phosphorus, potassium, calcium, magnesium, manganese, zinc and copper. The additional-Fe³⁺ treatment increased the chlorophyll index in plants compared with the As-treated plants. Among the elements, Fe concentration and accumulation specifically increased in the shoots of additional-Fe³⁺ plants compared with As-treated plants, indicating that As-induced chlorosis was Fe-chlorosis. Arsenic and Fe were mostly concentrated in the roots of the As-treated plants. Despite inducing chlorosis in the As-treated plants, phytosiderophores (PS) accumulation in the roots and release from the roots did not increase, rather PS accumulation decreased, indicating that As toxicity hindered PS production in the roots. The PS accumulation in the roots was further reduced in the additional-Fe³⁺ treatment.     

Monocot‐dicot variability in response to an iron oxide‐metallic iron source

Abstract

Iron from a mixture of Fe oxide and metallic Fe was more available to corn (Zea mays L.) than it was to soybeans when the plants wore grown in calcareous soil or in nutrient solution. All this Fe, however, was DTPA (diethylene triamine pentaacetic acid) extractable. In solution culture the Fe was available to the soybean (Glycine max L.) plants unless CaCO₃ was included in the nutrient solution.     

Manganese‐iron relationship in soybean grown in calcareous soils 1

Although a positive response to iron (Fe) is, usually, expected in calcareous soils; this has not been always the case; and in some instances a depressing effect has been observed. An induced micronutrient imbalance is suspected. This experiment was designed to study the effect of Fe fertilizer on the plant micronutrients. Twenty three highly calcareous soils (18–46% calcium carbonate equivalent; pH 7.7–8.4; and a wide range of extractable Fe) from southern Iran were used in an eight‐week greenhouse experiment to study the effect of Fe fertilizers on soybean [Glycine max (L.) Merr.] growth and chemical composition. The statistical design was a 23 × 3 factorial arranged in a completely randomized block with three replications. Treatments consisted of 23 soils and three levels of applied Fe (0, 10, and 20 mg Fe/kg as FeEDDHA). Uniform doses of nitrogen (N), phosphorus (P), copper (Cu), manganese (Mn), and zinc (Zn) were applied to all pots. Dry matter (DM) and micronutrients concentrations and uptakes of plant tops were determined and used as the plant responses. Application of Fe either had no significant effect on DM or even decreased it. The plant concentration and uptake of Fe increased significantly in all soils. The concentrations and uptakes of Cu and Zn did not change but those of Mn decreased significantly. The negative effect of Fe application was, therefore, attributed to the interference of Fe with Mn nutrition. The mechanism involved appears to be the restriction in Mn translocation from soil to root and/or from root to the plant tops.     

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.     

Phytosiderophore release from manganese‐induced iron deficiency in barley

An experiment was conducted in the phytotron with barley (Hordeum vulgare L. cv. Minorimugi) grown in nutrient solution to compare iron (Fe) deficiency caused by the lack of Fe with manganese (Mn)‐induced Fe deficiency. Dark brown spots on older leaves and stems, and interveinal chlorosis on younger leaves were common symptoms of plants grown in either Mn‐toxic or Fe‐deficient treatments. Dry matter yield was affected similarly by Fe deficiency and Mn toxicity. The Mn toxicity significantly decreased the translocation of Fe from roots to shoots, caused root browning, and inhibited Fe absorption. The rate of Fe translocated from roots to shoots in the 25.0 μM Mn (toxic) treatment was similar to the Fe‐deficient treatment. Manganese toxicity, based on the release of phytosiderophore (PS) from roots, decreased from 25.0>250>2.50 uM Mn. The highest release of PS from roots occurred 7 and 14 days after transplanting (DAT) to Mn‐toxic and Fe‐deficient treatments, respectively; but was always higher in the Fe‐deficient treatment than the Mn‐toxic treatments. The release of PS from roots decreased gradually with plant age and with severity of the Mn toxicity symptoms. The PS content in roots followed the PS release pattern.     

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.     

Tumorous crown gall response to iron‐deficiency stress in sunflower

Tumorous crown gall tissue in sunflower (Helianthus annus L.) initiates a mechanism for making Fe available to itself as evidenced by its ability to reduce Fe³⁺ to Fe²⁺. The objective of this study was to determine if a limited Fe supply to the plant might affect the growth, nutrition and reduction of Fe³⁺ to Fe²⁺ by the tumorous crown gall. Healthy green 14‐day‐old sunflower plants (cv mammoth Russian) were either stem‐inoculated with Agrobacterium tumefaciens to induce tumorous crown gall tissue development or were left uninoculated for comparison. The plants were grown in a modified Hoagland nutrient solution with treatments containing 0.0, 0.15, 0.6 and 2.0 mg Fe L^‐1. The 0 mg Fe L^‐1 treatment induced maximum Fe chlorosis, and consequently there was a release of hydrogen ions and of a yellow pigment by the roots, but there was no measureable release of ‘reductants’ by the roots. Iron‐deficiency stress (0 mg Fe L^‐1) also resulted in reduced tumorous crown gall growth, less reduction of Fe³⁺ to Fe²⁺, and lower levels of Fe in the tumorous tissue compared to tumorous tissues adequately supplied with Fe. The tumorous crown gall tissue on the stem reduced much more Fe³⁺ to Fe²⁺ than the nontumorous stem tissue regardless of Fe level in the treatment. Tumor tissue contained more Fe, Cu and P than the nontumorous stem tissues which may indicate a modified metabolism in this tissue. An abundant supply of Fe seems to enhance the development and growth of the tumorous crown gall tissue and a deficient supply of Fe retards its growth.     

Behavior of iron‐supplying materials in incubated calcareous soils 1

Two Fe chlorosis‐inducing calcareous soils were incubated for up to 5 months, at room temperature and field capacity, with Fe‐EDDHA, Fe‐DTPA, FeSO₄, an amino acid chelate “Fe‐Metalosate”;, an oxide “Micronized‐Iron”;, and a precipitated Fe‐S compound “Iron‐Sul”;. Other treatments included DTPA chelate alone, elemental S and H₂SO₄ at comparable rates. Both water‐soluble, and DTPA‐extractable Fe fractions were measured periodically from each sample. All water‐soluble sources decreased with time. Soluble Fe was highest after Fe‐EDDHA addition but was not detectable after “Fe‐Metalosate”; and FeSO₄. Acidification to neutralize CaCO₃ significantly increased DTPA‐extractable Fe, which remained high with increasing incubation time. “Micronized‐Iron”; and S had only a slight effect on DTPA‐ extractable Fe. Though Fe‐EDDHA is the most efficient Fe material, pelleted acidified Fe sources, i.e., “Iron‐Sul”;, may be more economical for some crops in the long term.     

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.     

Rice genotype differences in nutrient status under excessive ferric‐iron conditions

To investigate the relationship between rice genotypic variation in tolerance to iron (Fe) toxicity and nutrient element status, 10 rice genotypes with different growing performances under Fe toxicity were grown under normal culture solution and with excessive ferrous (Fe²⁺)‐Fe concentrations of 250 and 500 mg Fe²⁺ L^‐1. A close relationship was obtained between the relative ratio of symptomatic leaf numbers to total leaf numbers (SLN/TLN) and a relative decrease in dry matter under Fe²⁺‐toxicity conditions. The genotypic variations in nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) uptake were evaluated by the relative decrease in the N, P, K, and Mg content in the plants. Remarkable genotypic variation in tolerance to excessive Fe²⁺ was observed. The results indicated that excessive Fe²⁺ reduced N, P, K, and Mg uptake. The nutrient element concentrations, however, were still higher above deficient criteria even in severely affected plants, suggesting that the retardation of growth may not be intirely due to the deficiency of these elements in plants at the seedling stage. Significant correlations were found between the genotypic variation and the decrease in N, P, K, and Mg uptake and in their tolerance to Fe²⁺ toxicity, which suggests that the ability to maintain higher nutrient element uptake under a Fe²⁺‐toxic condition contributes the tolerance to Fe²⁺ toxicity.     

Environmental risks for application of iron and steel slags in soils in China: A review

Iron and steel slags are smelting wastes, mainly including blast furnace slag(BFS) and steel slag(SS) produced in the iron and steel industry. Utilization of iron and steel slags as resources for solving the problem of slag disposals has attracted much attention with increasing iron and steel smelting slags in China. Because the iron and steel slags contain calcium(Ca), magnesium(Mg), phosphorus(P), and silicon(Si), some have tried to use them as Si-and P-fertilizers, for producing Ca-Mg-P fertilizers, or as soil amendments in agriculture. However, in the iron metallurgical process, several pollutants in iron ores can inevitably transfer into iron and steel slags, resulting in the enrichment of pollutants both in BFS(mainly nickel(Ni), copper(Cu), mercury, zinc(Zn),cadmium(Cd), chromium(Cr), arsenic, lead, selenium, fluorine(F), and chlorine(Cl)) and in SS(mainly Ni, Cr, Cd, Zn, Cu, F, and Cl), in which some of pollutants(especially Cr, Ni, F, and Cl) exceed the limits of environmental quality standards for soils and groundwater. The elements of manganese, barium,and vanadium in iron and steel slags are higher than the background values of soil environment. In order to ensure soil health, food safety, and environmental quality, it is suggested that those industrial solid wastes, such as iron and steel slags, without any pretreatment for reducing harmful pollutants and with environmental safety risk, should not be allowed to use for soil remediation or conditioning directly in farmlands by solid waste disposal methods, to prevent pollutants from entering food chain and harming human health.     

Iron chlorosis in macadamia as affected by phosphate‐iron interactions 1

Iron (Fe) chlorosis induced by heavy phosphate (P) fertilizations is a serious problem for macadamia (Macadamia integrifolia) in Hawaii. To address this problem, a study was conducted to quantify the effects of P‐Fe interaction on macadamia leaf composition and chlorosis. The soil used was a limed Oxisol (Tropeptic Eutrustox, Wahiawa Series), pH 5.5. Phosphate was added as treble superphosphate at 0, 150 and 500 mg P/kg. The 150 mg P/kg rate was designed to yield approximately 0.04 mg P/L in the soil solution, a level considered adequate for macadamia growth. The 500 mg P/kg rate was intended to produce approximately 0.2 mg P/L, a level required by many horticultural crops but considered excessive for macadamia. Iron was added as Fe‐DTPA at 0, 5 and 10 mg Fe/kg soil, and factorially imposed on the P treatments. Color Index, a numerical rating based on hue, value and chroma from a Munsell Color Chart for Plant Tissues, was correlated with leaf chlorophyll concentration and used as an indicator of chlorosis.

Phosphate concentrations in leaves increased with increasing P application rates as expected, but decreased remarkably with increasing Fe rates (at a constant P rate). Plant Fe unexpectedly remained unchanged with increasing Fe rates but decreased with increasing P rates. The results suggest that (1) soil‐solution Fe was not a limiting factor to macadamia growth as is often incorrectly assumed for high P‐fertilized soils, (2) Fe uptake was restricted not because soil‐solution Fe was low but because plant P was excessively high, and (3) Fe translocation from roots to leaves may have been hampered by high P in the plants. Consequently, Fe chlorosis was intensified primarily by P fertilization (actually, by high plant P concentrations) and secondarily by P‐Fe interactions. Chlorosis, as measured by Color Index, can be diagnosed by a leaf Fe/P ratio < 0.06, and predicted by a soil‐solution ³√Fe/P ratio < 15.     

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.     

Aluminum and iron estimated by Mehlich‐3 extractant in mine soils in Galicia,northwest Spain

Abstract

The efficiency of Mehlich‐3 reagent as an extractant for aluminum (Al) and iron (Fe) was studied in Galician coal mine soils, in the process of reclamation. Mehlich‐3 Al and Fe values were compared to those from other Al and Fe tests and with phosphorus (P) sorption. The soils are very heterogeneous, consisting mainly of carbonaceous and non‐carbonaceous clays and shales, which are often rich in pyrite. Some of them have been amended with topsoil or fly ash. One hundred forty samples, from 0 to 15 or 15 to 30 cm, were analyzed. The pH values ranged from 2.7 to 8.4; oxalate and pyrophosphate Al from 0 to 1.17%, and 0.02 to 0.58%, respectively; and oxalate and pyrophosphate Fe from 0.02 to 2.25% and 0 to 1.28%, respectively; PSI (P sorption index) values varied between 0 and 55.1. The Mehlich‐3 Al values ranged from 24 to 2600 mg kg^‐1. A close relationship was observed between Mehlich‐3 and oxalate Al values (r=0.77), although the regression line tended to be curvilinear. Mehlich‐3 Al was better correlated than oxalate Al to pyrophosphate Al (r=0.66 vs. r=0.59) and also to pH‐NaF (r=0.89 vs. r=0.74). The Mehlich‐3 Al is almost as good as oxalate Al in estimating non‐crystalline Al, the correlation coefficients between log PSI and log (Mehlich‐3 Al) or log (oxalate Al) being 0.51 and 0.57, respectively. The Mehlich‐3 Fe correlated to available (r=0.63), exchangeable (r=0.65) and soluble Fe (r=0.66), but not to non‐crystalline Fe.     

An iron chelating compound released by barley roots in response to Fe‐deficiency stress

The excretion of phytosiderophores by barley (Hordeum vulgare L.) has recently been documented and a major difference in the Fe‐stress response of gramineous species and dicotyledonous species proposed. However, currently used methods of quantifying and measuring phytosiderophore are tedious or require specialized equipment and a cultivar easily accessible to U.S. scientists is needed. The objectives of this study were (a) to determine if “Steptoe”; and “Europa”; (used as a control cultivar) barleys would release Fe³⁺ solubilizing compounds in response to Fe‐deficiency stress and (b) to develop a technique to determine the efficiency of solubilization of Fe(OH)₃ by the released chelating substances. Two cultivars of barley were place under Fe‐stressed (‐Fe) and nonstressed (+Fe) conditions in modified Hoagland solutions (14 L). The solutions were periodically monitored for H⁺ and reductant release from the roots and plants were rated daily for chlorosis development. Periodic (6 or 7 harvests) evaluation of the release of Fe³⁺ solubilizing substances was performed as herein described. Neither H⁺ nor reductant extrusion occurred with either cultivar during Fe stress. However, Fe³⁺ solubilizing substances were released by both cultivars at relatively high levels under Fe‐stress conditions compared to the nonstressed plants. A convenient technique was developed to measure the release of Fe solubilizing substances released by barley roots.     

Is cooking food in iron pots an appropriate solution for the control of anaemia in developing countries? A randomised clinical trial in Benin

OBJECTIVE: To evaluate the effect of two types of iron pots on haemoglobin (Hb) and serum ferritin (SF) concentrations in young children (6-24 months), adolescent girls (11-15 years) and women of reproductive age (15-44 years), whose households were provided with iron pots for cooking food over a period of 6 months, compared with controls.Design and methodsWe randomly assigned 161 households including 339 individuals from the three subgroups to cast iron pots, blue steel pots or oral iron supplements (control). In the control group, children received micronutrient Sprinklestrade mark, and adolescent girls and women received iron tablets daily for 6 months. We measured Hb, SF and C-reactive protein concentrations at baseline and 6 months, and compared groups using regression models. RESULTS: Anaemia prevalence (Hb < 110 g l-1 in infants, Hb < 120 g l-1 in girls or women) was 47% (cast iron group), 50% (blue steel group) and 50% (control) at baseline. At 6 months, there were no significant differences in Hb concentrations among groups; however, differences in SF concentrations were significant (P < 0.0001) - the control group had higher SF concentrations compared with the groups using iron pots. Also, differences in the prevalence of iron-deficiency anaemia (IDA; anaemia plus SF < 15 mug l-1) were almost significant between cast iron and control groups (P = 0.08), and blue steel and control groups (P = 0.05).ConclusionThere is no evidence that iron cooking pots are effective against IDA. Further research is warranted to determine whether the iron leached from the pots is bioavailable.     

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.     

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.     

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.