Differences in Response to Iron Deficiency Among Some Lines of Common Bean

Abstract

Five dry bean cultivars (Coco blanc, Striker, ARA14, SVM29‐21, and BAT477) were evaluated for their resistance to iron deficiency on the basis of chlorosis symptoms, plant growth, capacity to acidify the external medium and the root‐associated Fe³⁺‐reduction activity. Plants were grown in nutrient solution supplied or not with iron, 45 µM Fe(III)EDTA. For all cultivars, plants subjected to iron starvation exhibited Fe‐chlorosis. These symptoms were more severe and more precocious in BAT477 and Coco blanc than in the others cultivars. An important acidification of the culture medium was observed between the 4th and the 8th days of iron starvation in Striker, SVM29‐21 and, particularly, ARA14 plants. However, all Fe‐sufficient plants increased the nutrient solution pH. This capacity of acidification appeared more clearly when protons extrusion was measured in 10 mM KCl + 1 mM CaCl₂. The above genotypic differences were maintained: ARA14 showed the higher acidification followed by Coco blanc and BAT477. Iron deficiency led also to an increase of the root‐associated Fe(III)‐reductase activity in all lines. However, genotypic differences were observed: Striker shows the highest capacity of iron reduction under Fe deficiency condition.     

Induction of in vivo root ferric chelate reductase activity in fruit tree rootstock

A method has been developed to consistently induce increases in root ferric chelate reductase activity in the fruit tree rootstock GF 677 (Prunus amygdalopersica) grown under iron (Fe) deficiency. Clonal GF 677 plants were grown hydroponically in a growth chamber with 0 or 90 μM Fe(III)‐EDTA. Root ferric chelate reductase activity was measured in vivo using BPDS. Plants grown without Fe developed visible symptoms of chlorosis and had lower root ferric chelate reductase activities than those grown with Fe. Root ferric chelate reductase activities were 0.1–1.9 and 0.6–5.3 nmol of Fe reduced per gram of fresh mass and minute, respectively, in Fe‐deficient and sufficient plants. However, when plants grown without Fe for several days were resupplied with 180 μM of Fe(III)‐EDTA, FC‐R activities increased within 1 day. The FC‐R values after Fe resupply were 20‐fold higher than those found in Fe‐deficient plants and 5‐fold higher than those found in the Fe‐sufficient controls. After three days of the Fe treatments the FC‐R activities had decreased again to the control values. The reduction of Fe was localized at the subapical root zone. In the conditions used we have found no decreases of the nutrient solution pH values, indicating that this type of response is not strong enough to be detected in peach tree rootstocks. Also, no major changes in root morphology have been found in response to Fe deficiency. This ferric chelate reductase induction protocol may be used in screening assays to select rootstock genotypes tolerant to Fe chlorosis.     

IRON IS REQUIRED FOR THE INDUCTION OF ROOT FERRIC CHELATE REDUCTASE ACTIVITY IN IRON-DEFICIENT TOMATO

Two mutants of tomato and their corresponding wild-type genotypes, Tfer/TFER and chloronerva/Bonner Beste, were grown in nutrient solution under conditions leading to iron (Fe) deficiency. Iron deficiency caused decreases in growth, leaf chlorosis, and changes in the morphology of roots. Ferric chelate reductase activities of whole roots were generally lower in Fe-deficient plants than in control, Fe-sufficient plants. Plants grown for 7 days without Fe, however, had transient increases in whole root ferric chelate reductase activity after the addition of small amounts of Fe (2 μM) to the nutrient solution. Also, adding sequential 0.5 μM Fe pulses to the nutrient solution led to high whole root ferric chelate reductase activities. Similar results were obtained with a protocol using excised root tips instead of whole root systems to measure ferric chelate reductase activities. The protocol using root tips generally gave higher ferric chelate reductase rates than the method using whole roots, due to the localized expression of the enzyme in the distal root zones.     

Uptake and apoplastic retention of EDTA‐ and phytosiderophore‐chelated chromium(III) in maize

Increasing the mobilization and root uptake of chromium (Cr) by synthetic and plant‐borne chelators might be relevant for the design of phytoremediation strategies on Cr‐contaminated sites. Short‐term uptake studies in maize roots supplied with ⁵¹CrCl₃ or ⁵¹Cr(III)‐EDTA led to higher apoplastic Cr contents in plant roots supplied with ⁵¹CrCl₃ and in Fe‐sufficient plants relative to Fe‐deficient plants, indicating that Fe stimulated co‐precipitation of Cr. Concentration‐dependent retention of Cr in a methanol:chloroform‐treated cell‐wall fraction was still saturable and in agreement with the predicted tendency of Cr(III) to precipitate as Cr(OH)₃. To investigate a possible stimulation of Cr(III) uptake by phytosiderophores, Fe‐deficient maize roots were exposed for 6 d to Cr(III)‐EDTA or Cr(III)‐DMA (2'‐deoxymugineic acid). Relative to plants without Cr supply, the supply of both chelated Cr species in a subtoxic concentration of 1 µM resulted in alleviation of Fe deficiency–induced chlorosis and higher Cr accumulation. Long‐term Cr accumulation from Cr(III)‐DMA was similar to that from Cr(III)‐EDTA, and Cr uptake from both chelates was not altered in the maize mutant ys1, which is defective in metal‐phytosiderophore uptake. We therefore conclude that phytosiderophores increase Cr solubility similar to synthetic chelators like EDTA, but do not additionally contribute to Cr(III) uptake from Cr‐contaminated sites.     

Response to iron‐deficiency stress of pear and quince genotypes 1

Roots of iron (Fe)‐efficient dicots react to Fe‐deficiency stress by strongly enhancing the ferric (Fe³⁺)‐reductase system and by lowering the rhizo‐sphere pH. In this study, we tested whether such adaptation mechanisms characterize pear and quince genotypes known to have differential tolerance to calcareous and alkaline soils. Two trials were performed using micropagated plants of three quince rootstocks (BA29, CTS212, and MC), three Pyrus communis rootstocks (OHxF51 and two selections obtained at the Bologna University: A28 and B21) and of two pear cultivars (Abbé Fétel and Bartlett, own‐rooted). In the first trial, plants were grown in a nutrient solution with [Fe(+)] and without [Fe(‐)] Fe for 50 days. Their root Fe‐reducing capacity was determined colorimetrically using ferrozine and FeEDTA, and Fe uptake of Fe(+) plants was estimated. In the second trial, the rhizosphere pH of plants grown in an alkaline soil was measured by a micro‐electrode. With the only exception of pears OHxF51 and A28, whose Fe‐reduction rates were similar in Fe(+) and Fe(‐) plants, the Fe‐deficiency stress resulted in a significant decrease in Fe reduction. Among the Fe(‐) plants, the two pear cultivars, OHxF51 and A28, had a higher Fe‐reducing capacity than the quince rootstocks and the cv. Abb6 F. When plants were pre‐treated with Fe, reduction rate was highest in the P. communis rootstocks, intermediate in the own‐rooted cultivars, and lowest in the quinces. Root Fe‐reducing capacity of Fe(+) plants proved to be linearly and positively correlated with Fe uptake and root proton release. Rhizosphere pH was highest in quince MC, intermediate in the other two quinces and in the cv. Abbe F., and lowest in the pear rootstocks and in the cv. Bartlett. Our results indicate that roots of pear and quinces do not increase their ability to reduce the Fe under Fe‐deficiency stress. The genotypical differential tolerance to Fe chlorosis likely reflects differences in the standard reductase system and in the capacity of lowering the pH at the soil/root interface. The determination of the root Fe‐reducing capacity is a promising screening technique for selecting pear root‐stocks efficient in taking up Fe.     

Strawberry recovers from iron chlorosis after foliar application of a grass‐clipping extract

Bare‐root transplants of strawberry (Fragaria × ananassa Duch. cv. Selva) were transferred to nutrient solutions with or without iron. After 35 d of growth, plants in the solution without iron became chlorotic and had morphological changes in roots typical of iron‐deficiency chlorosis (IDC). Acidification of the nutrient solution was also observed. We tested a grass‐clipping extract to correct IDC in strawberry plants by foliar application to some chlorotic plants. We also assessed the effects of this product on plant growth, Fe allocation, as well as morphological and physiological parameters related with IDC. After the second spray, leaf chlorophyll increased in the youngest expanded leaves. The total content of iron in plants increased from 1.93 mg to 2.37 mg per plant after three sprays, accounting for 80% of the total iron supplied by the extract. Newly formed roots from sprayed plants had a normal morphology (no subapical swollen zone) but a higher ferric chelate–reductase (FC‐R; EC 1.16.1.17) activity per root apex compared with roots from plants grown with iron or untreated chlorotic plants. Acidification of the nutrient solution continued in sprayed recovered plants. The results suggest an uncoupling of the regulation of morphological and physiological mechanisms related to IDC: FC‐R activity seems to be controlled by roots on their own or together with shoots, while morphological changes in roots are apparently regulated only by the level of iron in shoots.     

Factors related to iron uptake by dicotyledonous and monocotyledonous plants. I. pH and reductant

Some plants respond to Fe‐deficiency stress by inducing Fe‐solubilizing reactions at or near the root surface. In their ability to solubilize Fe, dicotyledonous plants are more effective than monocotyledonous plants. In this study we determined how representative plants differ in their response when subjected to Fe‐deficiency stress in a calcareous soil and in nutrient solutions. Iron‐inefficient genotypes of tomato, soybean, oats, and corn all developed Fe chlorosis when grown in soil, whereas Fe‐efficient genotypes of these same species remained green. The same genotypes were grown in complete nutrient solutions and then transferred to nutrient solutions containing N (as NO₃ ^‐) and no Fe.

The T3238 FER tomato (Lycopersican esculentum Mill.) Fe‐efficient) was the only genotype that released significant amounts of H from the roots (the pH was lowered to 3.9) and concomitantly released reductants. Under similar conditions, Hawkeye soyhean [Glycine max (L.) Merr.] released reductants but the solution pH was not lowered. Both Fe‐inefficient and Fe‐efficient genotypes of oats (Avena sativa L.) and corn (Zea mays L.) released insufficient H or reductant from their roots to solubilize Fe; as a result, each of these genotypes developed Fe‐deficiency (chlorosis).

The marked differences observed among these genotypes illustrate the genetic variability inherent within many plant species. A given species or genotype may accordingly not be adapted to a particular soil. Conversely, a given species or genotype may be found (or developed) that is precisely suited for a particular soil. In this event, the need for soil amendments may be reduced or eliminated.     

Uptake of Iron (59Fe) Complexed to Water‐Extractable Humic Substances by Sunflower Leaves

Abstract

A research was carried out to evaluate the leaves' ability to utilize Fe supplied as a complex with water‐extractable humic substances (WEHS) and the long‐distance transport of ⁵⁹Fe applied to sections of fully expanded leaves of intact sunflower (Helianthus annuus L.) plants. Plants were grown in a nutrient solution containing 10 µM Fe(III)‐EDDHA (Fe‐sufficient plants), with the addition of 10 mM NaHCO₃ to induce iron chlorosis (Fe‐deficient plants). Fe(III)‐WEHS could be reduced by sunflower leaf discs at levels comparable to those observed using Fe(III)‐EDTA, regardless of the Fe status. On the other hand, ⁵⁹Fe uptake rate by leaf discs of green and chlorotic plants was significantly lower in Fe‐WEHS‐treated plants, possibly suggesting the effect of light on photochemical reduction of Fe‐EDTA. In the experiments with intact plants, ⁵⁹Fe‐labeled Fe‐WEHS or Fe‐EDTA were applied onto a section of fully expanded leaves. Irrespective of Fe nutritional status, ⁵⁹Fe uptake was significantly higher when the treatment was carried out with Fe‐EDTA. A significant difference was found in the amount of ⁵⁹Fe translocated from treated leaf area between green and chlorotic plants. However, irrespective of the Fe nutritional status, no significant difference was observed in the absolute amount of ⁵⁹Fe translocated to other plant parts when the micronutrient was supplied either as Fe‐EDTA or Fe‐WEHS. Results show that the utilization of Fe complexed to WEHS by sunflower leaves involves an Fe(III) reduction step in the apoplast prior to its uptake by the symplast of leaf cells and that Fe taken up from the Fe‐WEHS complexes can be translocated from fully expanded leaves towards the roots and other parts of the shoot.     

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.     

Root and Leaf Ferric Chelate Reductase Activity in Pond Apple and Soursop

Abstract

Root and leaf ferric chelate reductase (FCR) activity in Annona glabra L. (pond apple), native to subtropical wetland habitats and Annona muricata L. (soursop), native to nonwetland tropical habitats, was determined under iron (Fe)-sufficient and Fe-deficient conditions. One-year-old seedlings of each species were grown with 2, 22.5, or 45 µM Fe in a nutrient solution. The degree of tolerance of Fe deficiency was evaluated by determining root and leaf FCR activity, leaf chlorophyll index, Fe concentration in recently mature leaves, and plant growth. Root FCR activity was generally lower in soursop than in pond apple. Eighty days after plants were put in nutrient solutions, leaf FCR activity of each species was lower in plants grown with low Fe concentrations (2 µM) than in plants grown with high (22.5 or 45 µM) Fe concentrations in the nutrient solution. Leaves of pond apple grown without Fe became chlorotic within 6 weeks. The Fe level in the nutrient solution had no effect on fresh and dry weights of soursop. Lack of Fe decreased the leaf chlorophyll index and Fe concentration in recently matured leaves less in soursop than in pond apple. The rapid development of leaf chlorosis in low Fe conditions and low root and leaf FCR activities of pond apple are probably related to its native origin in wetland areas, where there is sufficient soluble Fe for adequate plant growth and development. The higher leaf FCR activity and slower growth rate of soursop compared to pond apple may explain why soursop did not exhibit leaf chlorosis even under low Fe conditions.     

Activities of Iron‐Containing Enzymes in Leaves of Two Tomato Genotypes Differing in Their Resistance to Fe Chlorosis

Abstract

Two tomato (Lycopersicon esculentum Mill., cvs. Pakmor and Target) genotypes differing in resistance to iron (Fe) deficiency were grown in nutrient solution under controlled environmental conditions over 50 days to study the relationships between severity of leaf chlorosis, total concentration of Fe, and activities of Fe‐containing enzymes in leaves. The activities of Fe‐containing enzymes ascorbate peroxidase, catalase, and guaiacol peroxidase, and additionaly the activity of glutathione reductase, an enzyme that does not contain Fe, were measured. Plants were supplied with 2 × 10^?7 M (Fe deficient) and 10^?4 M (Fe sufficient) FeEDTA, respectively. Leaf chlorosis appeared more rapidly and severely in Target (Fe deficiency senstive genotype) than Pakmor (Fe deficiency resistant genotype). On day 50, Pakmor had 2‐fold more chlorophyll than Target under Fe deficiency, while at adequate supply of Fe the two genotypes were very similar in chlorophyll concentration. Despite distinct differences in development of leaf chlorosis and chlorophyll concentrations, Pakmor and Target were very similar in concentrations of total Fe under Fe deficiency. In contrast to Fe concentration, activities of Fe‐containing enzymes were closely related to the severity of leaf chlorosis. The Fe‐containing enzymes studied, especially catalase, showed a close relationship with the concentration of chlorophyll and thus differential sensitivity of tomato genotypes to Fe deficiency. Glutathione reductase did not show relationship between Fe deficiency chlorosis and enzyme activity. The results confirm that measurement of Fe‐containing enzymes in leaves is more reliable than the total concentration of Fe for characterization of Fe nutritional status of plants and for assessing genotypical differences in resistance to Fe deficiency. It appears that Fe deficiency‐resistant genotype contains more physiologically available Fe in tissues than the genotype with high sensitivity to Fe deficiency.     

Screening for resistance to iron deficiency chlorosis in dry bean using iron reduction capacity

Identifying cultivars resistant to iron (Fe) deficiency chlorosis so prevalent in calcareous soils is a more economical solution than fertilizer application in field crops. The current method of screening for resistance using chlorosis ratings in field trials is time consuming and highly variable. Root Fe reduction successfully separated cultivars or rootstocks, varying widely in resistance, of soybean (Glycine max L.), peach (Prunus persica L.), and grape (Vitis spp.), but was unsuccessful in sub‐clover (Trifolium subterraneum L.). Dry bean (Phaseolus vulgaris L.) exhibits Fe deficiency chlorosis in calcareous soils and initiates Fe reduction by the roots in response to such stress. The resistance of 24 dry bean cultivars to Fe deficiency chlorosis was assessed by measuring and summing daily Fe reduction by the roots. The cultivars were grown both hydroponically in an environmental chamber in low Fe solutions (0.05 mg‐L^‐1) and at three field sites in both 1995 and 1996. A significant relationship (P<0.01) between field chlorosis scores made 36 days after planting and root Fe reduction summations was observed for all sites in 1995 and 1996 (r = ‐0.42 to ‐0.71). The variability of chlorosis scores among sites, especially in 1996, points out the difficulty of using field chlorosis scores for screening. These results indicate that measurements of root Fe reduction can be used to predict resistance to Fe deficiency chlorosis in dry bean. Successful implementation of this technique should reduce if not eliminate field trials for screening resistance to Fe deficiency chlorosis.     

A greenhouse technique for screening Trifolium seedlings for iron‐deficiency chlorosis 1

Susceptible Trifolium plants often exhibit symptoms of iron (Fe)‐deficiency chlorosis when grown on high pH, calcareous soils. A greenhouse method was developed to screen seedlings for Fe‐deficiency chlorosis. ‘Yuchi’ arrowleaf (T. vesiculosum Savi.) and ‘Dixie’ crimson (I. incarnatum L.) clover seedlings were grown in “Super Cell”; Cone‐tainers in six calcareous Texas soils differing in Fe and selected other chemical characteristics. At the fourth trifoliolate leaf stage, chlorosis was induced by saturating the soil for a minimum of 2 weeks. The soils differed in their capacity to induce chlorosis in both clovers. Yuchi was more susceptible than Dixie, showing a higher percentage of chlorosis in five of the six soils. The results indicate that this screening method would be a useful tool for studying Fe‐deficiency chlorosis in Trifolium spp.     

Comparison of iron chelates and complexes supplied as foliar sprays and in nutrient solution to correct iron chlorosis of soybean

The application of synthetic chelates is the most efficient remedy for correcting iron (Fe) chlorosis. However, chelates are usually expensive and nondegradable products. Recently, new degradable chelates have been proposed for their use as Fe fertilizers. Also, Fe complexes cheaper than synthetic chelates and derived from natural products are also used to correct Fe deficiencies. Fifteen products, including five different synthetic chelates (Fe‐EDDS, Fe‐IDHA, and three Fe‐EDTA formulations) and ten natural complexes (humates, lignosulfonates, amino acids, glycoproteins, polyamines, citrate, and gluconate), have been compared when applied at low concentration to soybean (Glycine max L.) chlorotic plants grown in hydroponics under controlled conditions. In the first experiment, Fe compounds were applied to the nutrient solution, while in the second trial, Fe was foliar‐supplied. Dry matter, Fe concentration in shoots and roots, and SPAD values were used to evaluate the effectiveness of the Fe in the different products. In the nutrient‐solution experiment, synthetic chelates provided better plant growth, Fe concentration, and SPAD values than complexes. Among the Fe complexes, transferrin generally provided good plant responses, similar to those obtained with synthetic chelates. After foliar application, the highest regreening was observed for plants treated with synthetic chelates and amino acid complexes, but the translocation to roots only occurred for Fe lignosulfonate. Fe‐EDDS and Fe‐EDTA performed in a similar way when applied in nutrient solution or as foliar sprays.     

Response of five citrus rootstocks to iron deficiency

Citrus established in calcareous soils can be affected by iron (Fe)‐deficiency chlorosis which limits yield and the farmers' income. The degree of deficiency depends on the rootstock, but the resistance to Fe chlorosis still requires further investigation. To study physiological parameters of citrus rootstocks that could be used to evaluate resistance to Fe deficiency, plants of Troyer citrange (Citrus sinensis L. Osb. × Poncitrus trifoliata L. Raf.), Carrizo citrange, Volkamer lemon (Citrus volkameriana Ten. & Pasq.), alemow (Citrus macrophylla Wester), and sour orange (Citrus aurantium L.) were grown in nutrient solutions with 0, 5, 10, 15, or 20 μM Fe. For each rootstock, plant height, root and shoot dry weights, and concentration of Fe in the shoots and roots were measured at the end of the experiment. Chlorophyll (CHL) concentration was estimated throughout the experimental period using a portable CHL meter (SPAD‐502) calibrated for each rootstock. At the end of the experiment, CHL fluorescence parameters were measured in each rootstock with a portable fluorimeter. Maximal and variable fluorescence values indicated that the photochemistry of Troyer was more affected by a low concentration of Fe in the nutrient solution than that of other rootstocks. To compare rootstocks, the absolute CHL concentration was converted into relative yield by employing a scaling divisor based on the maximum value of total CHL in plants without Fe‐deficiency symptoms. Exponential models were developed to determine the minimum Fe concentration in nutrient solution required to maintain leaf CHL at 50% of the maximum CHL concentration (IC50). Models were also developed to assess the period of time the rootstocks were able to grow under Fe‐stress conditions before they reached IC50. Volkamer lemon and sour orange needed the lowest Fe concentration (between 4 and 5 μM Fe) to maintain IC50, and Troyer citrange had the highest Fe requirement (14 μM Fe). Citrus macrophylla and Carrizo citrange required 7 and 9 μM of Fe, respectively. Similarly, Volkamer lemon and sour orange rootstocks withstood more days under total Fe depletion or with a low concentration of Fe (5 μM Fe in nutrient solution) until they reached IC50, compared to the other rootstocks. The approach used led to a classification of the rootstocks into three categories, regarding their internal tolerance to Fe chlorosis: resistance (sour orange and Volkamer lemon), intermediate resistance (C. macrophylla and Carrizo citrange), and reduced resistance (Troyer citrange).     

Iron‐manganese interactions among clones of Nilegrass

Tetraploid clones of Nilegrass (Acroceras macrum, Stapf.) develop a chlorosis resembling iron (Fe) deficiency on acid (pH 5.0) soils in the Midlands of KwaZulu, Natal, South Africa. Hexaploid and pentaploid clones appear more resistant to the disorder. Iron deficiency would not be expected in such acid soils, but foliar sprays of Fe sulfate reduce the symptoms within 24 hours. Aluminum (Al) toxiciry has been ruled out as a cause of this chlorosis on the basis of soil tests. Manganese (Mn)‐induced Fe deficiency has been postulated. Six Nilegrass clones, differing in ploidy levels, were grown under low Fe or high Mn levels in nutrient solutions, in Mn‐toxic soil, in calcareous soil and in a standard potting soil at pH 7.0. Differential chlorosis symptoms, similar to those observed in the field, were reproduced in plants grown in low Fe or high Mn solutions, in neutral potting soil and in calcareous soil at pH 7.8. Based on plant symptoms and dry weights, the tetraploids were generally more sensitive to these conditions than hexaploid or pentaploid clones. However, in Mn‐toxic soil, plants had leaf tip necrosis rather than the chlorosis typical of Fe deficiency. When grown in a standard potting soil at pH 7.0, plants showing chlorosis accumulated higher concentrations of phosphorus (P), Al, copper (Cu), Mn, Fe, and zinc (Zn) than non‐chlorotic plants. Differential susceptibility to chlorosis is apparently associated with interference of such elements in Fe metabolism, and not with differential Fe concentrations in plant shoots. Additional studies are needed to determine the chemical states of Fe and Mn in root zones and within plant shoots of these clones. Resolution of the differential chlorosis phenomenon would contribute to fundamental knowledge in mineral nutrition and could be helpful in tailoring plant genotypes to fit problem soils.     

Physiological responses of grapevine callus cultures to iron deficiency

Grapevine is considered a ‘Strategy I’ plant because it performs some peculiar biochemical and physiological responses when grown under iron (Fe) deficiency stress conditions. Callus cultures were started from leaf and internode cuts of micropropagated plantlets of two grapevine genotypes well known for their Fe‐chlorosis characteristic: Vitis riparia a very susceptible genotype and Vitis berlandieri a resistant one. Modification of NADH: ferric (Fe³⁺) reductase activity was spectrophotometrically evaluated by following the formation of the complex ferrous (Fe²⁺)‐(BPDS)₃, while the malic and citric acid production were determined in callus cultures grown both in the presence (+Fe) and absence (‐Fe) of Fe. Moreover, a microsomal fraction was isolated from the calli to evaluate the H⁺‐ATPase and the Fe³⁺‐EDTA reductase activities. As expected, calli of the Fe‐efficient genotype (V. berlandieri) was able to enhance Fe³⁺‐EDTA reductase activity when growing under Fe deficiency while the Fe‐chlorosis susceptible V. riparia could not or did it with lower efficiency. Therefore, the H⁺‐ATPase assay showed a higher enzymatic activity in the microsomal fraction isolated from Vitis berlandieri grown without Fe with respect to its control (+Fe). Organic acid determination gave quite contradictory results, specially regarding malic acid which, under our study conditions, seemed not to be linked with the strategies of response to Fe deficiency.     

ROOT FERRIC CHELATE REDUCTASE IS REGULATED BY IRON AND COPPER IN STRAWBERRY PLANTS

In the present experiment, we studied the interaction between copper (Cu) and iron (Fe) in strawberry plants grown in nutrient solutions containing different concentrations of Fe. Plants grown in the absence of iron (Fe0) had the characteristic symptoms of Fe deficiency, with smaller chlorotic leaves, less biomass, acidification of the nutrient solution, and roots that were smaller and less ramified, while no symptoms of Fe deficiency were observed in plants grown with Fe. A greater amount of Cu was found in roots of chlorotic plants than in those grown with Fe, while plants grown with 20 μM of Fe (Fe20) in the nutrient solution had a greater amount of Fe compared with plants from the other treatments. Chlorotic plants (Fe0) and plants grown with the greatest level of Fe (Fe20) had a greater root ferric chelate reductase (FC-R; EC 1.16.1.17) activity compared with the other treatments with 5 or 10 μM Fe in the nutrient solution. The same pattern was obtained for relative FC-R mRNA concentration and for the sum of Fe and Cu contents in shoots (leaves plus crowns). The DNA obtained from amplification of the FC-R mRNA was cloned and several of the inserts analysed by single strand confirmation polymorphism (SSCP). Although there were different SSCP patterns in the Fe20 treatment, all the inserts that were sequenced were very similar, excluding the hypothesis of more than one FC-R mRNA species being present. The results suggest that Cu as well as Fe is involved in FC-R expression and activity, although the mechanism involved in this regulation is unknown so far. Both small contents of Fe and Cu in plants led to an over-expression of the FC-R gene and enhanced FC-R activity in strawberry roots.     

Iron‐stress response of inoculated and non‐inoculated roots of an iron inefficient soybean cultivar in a split‐root system

The objective of this study was to establish whether the iron‐stress responses observed in T203 soybean (Fe‐inefficient) with active nodules are products of the nodules or of the entire root system. A split‐root system was used in which half the roots of each plant were inoculated and actively fixing nitrogen and the other half were not. Soybean cultivar T203 is normally Fe‐inefficient and does not exhibit the Fe‐stress responses, however an iron‐stress response did occur during active N₂ fixation in earlier studies. This implies that the active nodules influenced the plant's ability to respond to Fe‐deficiency stress. In this study, the Fe‐stress response (H⁺ and reductant release) observed in T203 soybean was limited to the inoculated side of the split‐root system. The severe Fe chlorosis which developed in these plants was overcome in a manner similar to Fe‐efficient cultivars undergoing normal Fe‐stress response and the T203 plants completely regreened. Exudation of H⁺ ions was similar in both the presence and absence of Fe, and was generally limited to inoculated roots. Reductant release was nearly nonexistent from the non‐inoculated roots and was greater for the Fe‐stressed (‐Fe) plants than for non‐stressed (+Fe) plants. Thus, the response observed, which alleviated Fe chlorosis, appeared to be associated with N₂ fixation of the active nodules.     

Genetic Differences in Resistance to Iron Deficiency Chlorosis in Peanut

Iron (Fe) deficiency has been a widespread problem in peanut (Arachis hypogaea L.) grown on calcareous soils of northern China and has resulted in significant yield losses. Field observations showed considerable variability in visual chlorosis symptoms among peanut cultivars in the same soil. The objective of this study was to confirm the genetic differences in resistance to Fe-deficiency chlorosis in peanut and to identify feasible indicators for screening Fe-efficient genotypes. Resistance to Fe chlorosis of sixteen peanut cultivars grown on calcareous soil was evaluated in the field and physiological responses to Fe-deficiency stress were studied in nutrient solution. There were significant differences in resistance to Fe-deficiency chlorosis among the sixteen peanut cultivars tested, which was identified with SPAD readings, active Fe concentrations in young leaves in the early growth stages, and the pod yield. For Fe-resistant peanut cultivars, Fe-reduction capacity and quality of releasing hydrogen ions from roots increased under Fe-deficiency stress. Highly correlated relationships were observed between the summation of root Fe reduction and field chlorosis scores for sixteen cultivars (r² = 0.79). It was concluded that Fe-reduction capacity was a better physiological indicator for screening Fe-efficient peanut genotypes of the mechanisms measured.