Tolerance To Fe Deficiency Research Articles

Iron Deficiency Tolerance at Leaf Level in <i>Medicago ciliaris</i> Plants

Iron deficiency is an important environmental factor restricting plant productivity. Selecting tolerant genotypes is one of the possible ways to solve this problem. Many studies reported the effects of Fe deficiency on photosynthesis and anti-oxidative defense system. Yet, there is little information available on the use of these attributes as selective criteria. In the present study, we aim to determine some physiological and biochemical traits conferring Fe deficiency tolerance at leaf level in two lines of Medicago ciliaris. Our results showed that Fe deprivation had a lowering effect on photosynthesis (chlorophyll, photosynthetic electron transport activity and chlorophyll fluorescence) in both lines studied. However, the sensitive line TN8.7 was more affected. Hydrogen peroxide concentration was negatively correlated with the activities of antioxidant enzymes and with the concentration of some non-enzymatic antioxidant. The tolerant line TN11.11 was characterized by a more efficient antioxidant defense system in comparison with the sensitive line TN8.7. The main conclusion of this study is that photosynthesis and antioxidant defense system could be used as physiological and biochemical indicators of Fe deficiency tolerance in Medicago ciliaris plants.

Iron biofortification of rice using different transgenic approaches.

More than 2 billion people suffer from iron (Fe) deficiency, and developing crop cultivars with an increased concentration of micronutrients (biofortification) can address this problem. In this review, we describe seven transgenic approaches, and combinations thereof, that can be used to increase the concentration of Fe in rice seeds. The first approach is to enhance the Fe storage capacity of grains through expression of the Fe storage protein ferritin under the control of endosperm-specific promoters. Using this approach, the concentration of Fe in the seeds of transformants was increased by approximately 2-fold in polished seeds. The second approach is to enhance Fe translocation by overproducing the natural metal chelator nicotianamine; using this approach, the Fe concentration was increased by up to 3-fold in polished seeds. The third approach is to enhance Fe influx to the endosperm by expressing the Fe(II)-nicotianamine transporter gene OsYSL2 under the control of an endosperm-specific promoter and sucrose transporter promoter, which increased the Fe concentration by up to 4-fold in polished seeds. The fourth approach is introduction of the barley mugineic acid synthesis gene IDS3 to enhance Fe uptake and translocation within plants, which resulted in a 1.4-fold increase in the Fe concentration in polished seeds during field cultivation. In addition to the above approaches, Fe-biofortified rice was produced using a combination of the first, second, and third approaches. The Fe concentration in greenhouse-grown T2 polished seeds was 6-fold higher and that in paddy field-grown T3 polished seeds was 4.4-fold higher than in non-transgenic seeds without any reduction in yield. When the first and fourth approaches were combined, the Fe concentration was greater than that achieved by introducing only the ferritin gene, and Fe-deficiency tolerance was observed. With respect to Fe biofortification, the introduction of multiple Fe homeostasis genes is more effective than the introduction of individual genes. Moreover, three additional approaches, i.e., overexpression of the Fe transporter gene OsIRT1 or OsYSL15, overexpression of the Fe deficiency-inducible bHLH transcription factor OsIRO2, and knockdown of the vacuolar Fe transporter gene OsVIT1 or OsVIT2, may be useful to further increase the Fe concentration of seeds.

Iron deficiency in plants: an insight from proteomic approaches

Iron (Fe) deficiency chlorosis is a major nutritional disorder for crops growing in calcareous soils, and causes decreases in vegetative growth as well as marked yield and quality losses. With the advances in mass spectrometry techniques, a substantial body of knowledge has arisen on the changes in the protein profiles of different plant parts and compartments as a result of Fe deficiency. Changes in the protein profile of thylakoids from several species have been investigated using gel-based two-dimensional electrophoresis approaches, and the same techniques have been used to investigate changes in the root proteome profiles of tomato (Solanum lycopersicum), sugar beet (Beta vulgaris), cucumber (Cucumis sativus), Medicago truncatula and a Prunus rootstock. High throughput proteomic studies have also been published using Fe-deficient Arabidopsis thaliana roots and thylakoids. This review summarizes the major conclusions derived from these “-omic” approaches with respect to metabolic changes occurring with Fe deficiency, and highlights future research directions in this field. A better understanding of the mechanisms involved in root Fe homeostasis from a holistic point of view may strengthen our ability to enhance Fe-deficiency tolerance responses in plants of agronomic interest.

Isolation and functional characterization of MxCS1: a gene encoding a citrate synthase in Malus xiaojinensis

Iron is one of the essential micronutrients required by all living organisms. In this study, we isolated a gene encoding putative citrate synthase (CS) from Malus xiaojinensis, designated as MxCS1. The MxCS1 gene encodes a protein of 473 amino acid residues with a predicted molecular mass of 52.5 kDa and a theoretical isoelectric point of 8.67. The expression of MxCS1 was enriched in the leaf rather than in phloem and root, however, its expression was hardly detected in the xylem. The gene expression was strongly induced by Fe stress treatment in the M. xiaojinensis seedlings. Over-expression of MxCS1 improved Fe deficiency tolerance in transgenic Arabidopsis. We argued that MxCS1 is a new member of the CS genes, and it may function as a regulator in response to iron stress in plants.

Isolation and functional characterization of MxCS1: a gene encoding a citrate synthase in Malus xiaojinensis

Iron is one of the essential micronutrients required by all living organisms. In this study, we isolated a gene encoding putative citrate synthase (CS) from Malus xiaojinensis, designated as MxCS1. The MxCS1 gene encodes a protein of 473 amino acid residues with a predicted molecular mass of 52.5 kDa and a theoretical isoelectric point of 8.67. The expression of MxCS1 was enriched in the leaf rather than in phloem and root, however, its expression was hardly detected in the xylem. The gene expression was strongly induced by Fe stress treatment in the M. xiaojinensis seedlings. Over-expression of MxCS1 improved Fe deficiency tolerance in transgenic Arabidopsis. We argued that MxCS1 is a new member of the CS genes, and it may function as a regulator in response to iron stress in plants.

NO synthase-generated NO acts downstream of auxin in regulating Fe-deficiency-induced root branching that enhances Fe-deficiency tolerance in tomato plants

In response to Fe-deficiency, various dicots increase their root branching which contributes to the enhancement of ferric-chelate reductase activity. Whether this Fe-deficiency-induced response eventually enhances the ability of the plant to tolerate Fe-deficiency or not is still unclear and evidence is also scarce about the signals triggering it. In this study, it was found that the SPAD-chlorophyll meter values of newly developed leaves of four tomato (Solanum lycocarpum) lines, namely line227/1 and Roza and their two reciprocal F1 hybrid lines, were positively correlated with their root branching under Fe-deficient conditions. It indicates that Fe-deficiency-induced root branching is critical for plant tolerance to Fe-deficiency. In another tomato line, Micro-Tom, the increased root branching in Fe-deficient plants was accompanied by the elevation of endogenous auxin and nitric oxide (NO) levels, and was suppressed either by the auxin transport inhibitors NPA and TIBA or the NO scavenger cPTIO. On the other hand, root branching in Fe-sufficient plants was induced either by the auxin analogues NAA and 2,4-D or the NO donors NONOate or SNP. Further, in Fe-deficient plants, NONOate restored the NPA-terminated root branching, but NAA did not affect the cPTIO-terminated root branching. Fe-deficiency-induced root branching was inhibited by the NO-synthase (NOS) inhibitor L-NAME, but was not affected by the nitrate reductase (NR) inhibitor NH4+, tungstate or glycine. Taking all of these findings together, a novel function and signalling pathway of Fe-deficiency-induced root branching is presented where NOS-generated rather than NR-generated NO acts downstream of auxin in regulating this Fe-deficiency-induced response, which enhances the plant tolerance to Fe-deficiency.

Effects of 4-month Fe deficiency exposure on Fe reduction mechanism, photosynthetic gas exchange, chlorophyll fluorescence and antioxidant defense in two peach rootstocks differing in Fe deficiency tolerance

Fe deficiency was imposed by omission of Fe (-Fe), or by inclusion of bicarbonate (supplied as 20 mM NaHCO3) in the nutrient solution in two contrasting peach rootstocks (GF-677; tolerant to Fe deficiency and Cadaman; sensitive to Fe deficiency) for 4 months. In the Fe-deprived leaves and roots, and especially in those treated with bicarbonate, a decrease in Fe concentrations was recorded. Omission of Fe resulted in an increase of the activity of root Fe(III)-chelate reductase (FCR) in both rootstocks, whereas FCR activity decreased in the bicarbonate-treated roots of Cadaman. The results obtained from the FCR assay were confirmed by an agarose-based staining technique used to localize FCR activity. Also, an agar-pH-test revealed that the roots of GF-677 exposed to (-Fe) treatment induced a strong H+ extrusion. In addition, Fe deficiency resulted in reduction of the total chlorophyll (CHL) content. Apart from the (-Fe)-treated leaves of GF-677, Fe deficiency caused a decline in the photosynthetic rate (P(n)) and stomatal conductance (g(s)), without changes of the intercellular CO2 concentration (C(i)), as well as a reduction in the maximum quantum yield of PSII (F(v)/F(m)) and the ratio between variable to initial fluorescence F(v)/F0. The above changes were particularly evident for the bicarbonate-treated leaves of Cadaman. On the other hand, Fe deficiency resulted in an increase of leaf superoxide dismutase (SOD) activity and a depression of catalase (CAT) activity in the leaves and roots, irrespective of the rootstock. Although the non-enzymatic antioxidant activity (FRAP values) was increased in the roots of both rootstocks exposed to -Fe treatment, however, FRAP values were stimulated in the (-Fe)-treated leaves of GF-677 and decreased in the bicarbonate-treated leaves of Cadaman. The H2O2 content was increased in Fe-deprived tissues except for the (-Fe)-treated leaves and roots of GF-677. As a result of Fe deficiency, peroxidase (POD) activity and isoform expression were diminished in the tissues of Cadaman. However, in the tissues of GF-677 subjected to -Fe treatment POD activity was increased whereas an additional POD isoform was detected in the roots suggesting that expression of POD isoforms might be an important attribute linked to the tolerance to Fe deficiency.

Physiological root responses of iron deficiency susceptible and tolerant tomato genotypes and their reciprocal F1 hybrids

By using two tomato genotypes line 227/1 (Fe chlorosis susceptible) and Roza (Fe chlorosis tolerant) and their reciprocal F1hybrid, some root morphological changes, pH changes of nutrient solution, reduction capacity of FeIII and uptake and root-to-shoot translocation of 59Fe were studied under controlled environmental conditions in nutrient solution with 3 different Fe supplies as Fe EDDHA (i.e., 10−7 M, severe Fe deficiency; 10−6 M, intermediate Fe deficiency; 10−4 M, adequate Fe supply). Tolerant parent `Roza' was less affected by low Fe supply than susceptible parent `line 227/1' as judged from the severity of leaf chlorosis. Under both Fe deficient conditions there were no differences between the reciprocal hybrids concerning the appearance of chlorosis. Under intermediate Fe deficiency, reciprocal F1 hybrids (`line 227/1 × Roza' and `Roza × line' 227/1) showed an intermediate chlorosis between tolerant and susceptible parents. However, under severe Fe deficiency the reciprocal hybrids were more chlorotic than the tolerant parent irrespective of which parent was the cytoplasm contributor. A decreased Fe supply during preculture enhanced FeIII reduction capacities of the parents and reciprocal hybrids. Differences in the tolerance to Fe deficiency always were better correlated with FeIII reduction capacity of the genotypes than the Fe deficiency-induced release of H+ ions. Under both Fe deficient conditions the tolerant parent Roza had a much higher FeIII reduction capacity than the susceptible parent line 227/1. The reduction capacity of the hybrids `Roza × line 227/1' was very similar to the capacity of the parent Roza, but higher than the capacity of the hybrids `line 227/1×Roza' at both Fe-deficient conditions. Under both Fe deficient conditions tolerant parent had higher number of lateral roots than the susceptible parent. Among the reciprocal hybrids `Roza × line 227/1' possessed more lateral roots than the `line 227/1 × Roza' under both Fe deficient conditions. Low Fe nutritional status resulted in marked increase in root uptake of 59Fe. At adequate Fe supply, reciprocal hybrids and their parents did not differ in uptake and root-to-shoot translocation of Fe. However, under Fe-deficient conditions uptake and root-to-shoot translocation of 59Fe were significantly higher in the Fe chlorosis tolerant than the susceptible parent. Based on the reduction capacity of FeIII and uptake and root-to-shoot translocation of Fe, the F1 hybrids obtained from the cross in which the maternal genotype was Roza appeared to be more tolerant than when the maternal genotype was the susceptible line 227/1. Uptake and translocation ratio of the F1 hybrids obtained from `Roza × line 227/1' were similar to those of the parent Roza, but higher than the F1 hybrids obtained from `line 227/1 × Roza', particularly under intermediate Fe deficiency. The results indicate that FeIII reduction show a better relationship to Fe efficiency than Fe deficiency induced release of H+ ions. The inheritance of Fe deficiency tolerance of Roza seems not to be simple monogenic. It might be characterised by both, nuclear and extranuclear heredity. The intermediate responses of the reciprocal hybrids of the `line 227/1 × Roza' indicates that the Fe deficiency tolerance character of Roza is transferable by nuclear heredity. The better responses of the hybrids of `Roza × line 227/1' than the hybrids of `line 227/1 × Roza' may be due to maternal transmission from the parent Roza besides the nuclear transmission.

Presence of nicotianamine synthase isozymes and their homologues in the root of graminaceous plants

Nicotianamine synthase (NAS) catalyzes the synthesis of nicotianamine, which is an intermediate in the biosynthetic pathway of mugineic acid family phytosiderophores (MAs). Using polyclonal anti-NAS antibodies and recombinant NAS proteins, we identified five NAS isozymes and one NAS homologue in Fe-deficient barley roots using two-dimensional electrophoresis followed by Western blot analysis. Other unidentified NAS homologues that were induced by Fe-deficiency were also detected in barley roots. Western analysis enabled to detect NAS homologues in wheat, oats, rice, maize, and sorghum roots. In graminaceous species, both the amount and number of NAS homologues were correlated with the total NAS activity and Fe-deficiency tolerance. The NAS isoform patterns differed among the graminaceous plants.

Immunological characterization of a 36 kDa Fe deficiency specific peptide in barley roots

In a previous paper we reported that an acidic 36 kDa peptide is the most strongly induced peptide among several peptides induced by Fe deficiency in barley roots. In this paper, polyclonal antibodies were raised against the 36 kDa peptide. This peptide appeared in the roots of all the graminaceous species tested (barley, rye, wheat, oat, maize, sorghum and rice) in response to Fe deficiency. More of the peptide was found in the roots of graminaceous species which secrete higher amounts of mugineic acids (MAs) under Fe deficient nutrition status. Induction of the 36 kDa peptide was first observed on the third day of Fe deficiency, rising to a maximum value on the seventh day. The trend has a positive correlation with secretion of MAs during Fe deficiency. Further, resupply of Fe resulted in a decrease in peptide production on the second day, reaching a control level on the seventh day. The rate of decrease in peptide production was observed to be slower than that of MA secretion. Other nutrient stresses such as B excess, B deficiency, Cu excess, Cu deficiency, Mn excess, Mn deficiency, Zn excess and Zn deficiency induced far less of the peptide. The specific expression of the 36 kDa peptide in roots of graminaceous species under Fe deficiency suggested the positive association of the peptide with a specific Fe deficiency tolerance mechanism in graminaceous plants.

Mechanisms of Fe-deficiency tolerance in crop cultivars: Effects of dibutyl phthalate and caffeic acid on Fe-chlorosis recovery

Abstract Several crop cultivars were tested for their Fe‐deficiency stress tolerance and susceptibility, using solution culture with Fe and without Fe. The criteria employed were the onset of and recovery from chlorosis and change in pH. While in sorghum, peanut, cotton, sesame, and chickpea, the recovery was associated with decrease in pH, there was no relationship between these two factors in lentil, in which two cultivars behaved differently. In VI‐1, the pH decreased only to a small extent, but the plants turned green. On the other hand, in S‐34, the pH decreased considerably but no recovery was obtained. In sorghum and jute, we identified DBP (dibutyl phthalate) in the stress medium of tolerant cultivars (Kannan et a]. 1984; Ramani et al. 1986) and the addition of DBP caused the chlorotic sorghum and jute to recover from chlorosis. The chemical from the nutrient medium of Fe‐stressed tomato cultivars was extracted and identified as caffeic acid. However, plants within cultivars of tomato and sorghum ...