Iron availability in plant tissues-iron chlorosis on calcareous soils

The article describes factors and processes which lead to Fe chlorosis (lime chlorosis) in plants grown on calcareous soils. Such soils may contain high HCO₃ ^- concentrations in their soil solution, they are characterized by a high pH, and they rather tend to accumulate nitrate than ammonium because due to the high pH level ammonium nitrogen is rapidly nitrified and/or even may escape in form of volatile NH₃. Hence in these soils plant roots may be exposed to high nitrate and high bicarbonate concentrations. Both anion species are involved in the induction of Fe chlorosis.Physiological processes involved in Fe chlorosis occur in the roots and in the leaves. Even on calcareous soils and even in plants with chlorosis the Fe concentration in the roots is several times higher than the Fe concentration in the leaves. This shows that the Fe availability in the soil is not the critical process leading to chlorosis but rather the Fe uptake from the root apoplast into the cytosol of root cells. This situation applies to dicots as well as to monocots. Iron transport across the plasmamembrane is initiated by Fe^III reduction brought about by a plasmalemma located Fe^III reductase. Its activity is pH dependent and at alkaline pH supposed to be much depressed. Bicarbonate present in the root apoplast will neutralize the protons pumped out of the cytosol and together with nitrate which is taken up by a H⁺/nitrate cotransport high pH levels are provided which hamper or even block the Fe^III reduction.Frequently chlorotic leaves have higher Fe concentrations than green ones which phenomenon shows that chlorosis on calcareous soils is not only related to Fe uptake by roots and Fe translocation from the roots to the upper plant parts but also dependent on the efficiency of Fe in the leaves. It is hypothesized that also in the leaves Fe^III reduction and Fe uptake from the apoplast into the cytosol is affected by nitrate and bicarbonate in an analogous way as this is the case in the roots. This assumption was confirmed by the highly significant negative correlation between the leaf apoplast pH and the degree of iron chlorosis measured as leaf chlorophyll concentration. Depressing leaf apoplast pH by simply spraying chlorotic leaves with an acid led to a regreening of the leaves.     

Rhizosphere acidification and Fe3+ reduction in lupins and peas: Iron deficiency in lupins is not due to a poor ability to reduce Fe3+

While lupins suffer severely from Fe deficiency when grown on calcareous soils, field peas under the same conditions grow normally. This paper aimed to identify whether these differences were related to differences in either the pattern or capacity for rhizosphere acidification or Fe³⁺ reduction between these species. Two lupin species (Lupinus angustifolius, L. cosentinii) and field peas (Pisum sativum) were grown in solution culture for 5 weeks with both an adequate and a low supply of Fe. Plants were reliant on symbiotically fixed N. The extent of iron reduction was determined using the chelates TPTZ and BPDS. The pattern of reactions around roots was determined by placing roots in agar containing either bromocresol purple or TPTZ. The low supply of Fe decreased the growth of lupins by over 30% and induced severe chlorosis and necrosis. Growth of the peas was reduced by less than 15% and no symptoms appeared. All species acidified the solutions by about 1 pH unit regardless of the Fe treatment. The level of Fe³⁺ reduction was higher for all species grown with low Fe than with adequate Fe. Capacity for Fe³⁺ reduction was higher for all species grown with low Fe than with adequate Fe. Capacity for Fe³⁺ reduction was similar for all species. The pattern of acidification and reduction around roots was also similar between species. Thus it appears that the capacity of lupins to reduce Fe³⁺ in the rhizosphere is not the primary cause of Fe deficiency in lupins.     

The calcium nutrition of bambara groundnut (Vigna subterranea (L.) Verdc.)

Iron chlorosis induced by Fe-deficiency is a widespread nutritional disorder in many woody plants and in particular in grapevine. This phenomenon results from different environmental, nutritional and varietal factors. Strategy I plants respond to Fe-deficiency by inducing physiological and biochemical modifications in order to increase Fe uptake. Among these, acidification of the rhizosphere, membrane redox activities and synthesis of organic acids are greatly enhanced during Fe-deficiency. Grapevine is a strategy I plant but the knowledge on the physiological and biochemical responses to this iron stress deficiency in this plant is still very poor. In this work four different genotypes of grapevine were assayed for these parameters. It was found that there is a good correlation between genotypes which are known to be chlorosis-resistant and increase in both rhizosphere acidification and Fe^III reductase activity. In particular, when grown in the absence of iron, Vitis berlandieri and Vitis vinifera cv Cabernet sauvignon and cv Pinot blanc show a higher capacity to acidify the culture medium (pH was decreased by 2 units), a higher concentration of organic acids, a higher resting transmembrane electrical potential and a greater capacity to reduce Fe^III-chelates. On the contrary, Vitis riparia, well known for its susceptibility to iron chlorosis, fails to decrease the pH of the medium and shows a lower concentration in organic acids, lower capacity to reduce Fe^III and no difference in the resting transmembrane electrical potential. H Marschner Section editor     

Mechanism of Fe uptake by the leaf symplast: Is Fe inactivation in leaf a cause of Fe deficiency chlorosis?

The mechanism of iron (Fe) uptake from the leaf apoplast into leaf mesophyll cells was studied to evaluate the putative Fe inactivation as a possible cause of Fe deficiency chlorosis. For this purpose, sunflower (Helianthus annuus L.) and faba bean plants (Vicia faba L.) were precultured with varied Fe and bicarbonate (HCO ₃ ^- ) supply in nutrient solution. After 2–3 weeks preculture, Fe^III reduction and ⁵⁹Fe uptake by leaf discs were measured in solutions with Fe supplied as citrate or synthetic chelates in darkness. The data clearly indicate that Fe^III reduction is a prerequisite for Fe uptake into leaf cells and that the Fe nutritional status of plants does not affect either process. In addition, varied supply of Fe and HCO ₃ ^- to the root medium during preculture had no effect on pH of the xylem sap and leaf apoplastic fluid. A varied pH of the incubation solution had no significant effect on Fe^III reduction and Fe uptake by leaf discs in the physiologically relevant pH range of 5.0–6.0 as measured in the apoplastic leaf fluid. It is concluded that Fe inactivation in the leaf apoplast is not a primary cause of Fe deficiency chlorosis induced by bicarbonate. This revised version was published online in June 2006 with corrections to the Cover Date.     

Functional Analysis of the Genotypic Differences in Response of Pea (<i>Pisum sativum</i> L.) to Calcareous-Induced Iron Deficiency

Lime-induced iron chlorosis is a major nutritional disorder causing severe plant growth and yield reduction in the calcareous soils of Tunisia. The understanding the behavior of key metabolic functions of peas on calcareous soils, the identification of useful traits of tolerance, and the exploration of the genotypic differences in response to this constraint remain the most efficient approaches due to their coast, environmental benefits, and sustainability. For this purpose, a greenhouse experiment was conducted on three pea genotypes (Alexandra: Alex, Douce de provence: DP, and Merveille de Kelvedon: MK) cultivated on calcareous soil (Fe-deficient) and fertile soil (control). Plant growth, SPAD index, iron nutrition and distribution, photosynthesis, and antioxidant enzymes were deeply analyzed to discriminate genotypic differences. Calcareous-induced iron deficiency reduced SPAD index, plant growth, net photosynthesis, and tissue Fe content against a significant stimulation of the oxidative stress indicators, H₂O₂ and Malondialdehyde (MDA). Moreover, we reported a significant induction of SOD and CAT activity in shoots and roots of the Alexandra genotype. Fe use efficiency increased on calcareous soil and clearly discriminated the studied genotypes. Alexandra genotype was found to be the most tolerant to lime-induced iron chlorosis. This genotype protects its tissues against oxidative stress by stimulating enzyme activities (SOD and CAT) and develops significant efficiency of Fe uptake, translocation to shoots and use when cultivated on calcareous soil.     

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 Fe^III 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 Fe^III reduction capacities of the parents and reciprocal hybrids. Differences in the tolerance to Fe deficiency always were better correlated with Fe^III 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 Fe^III 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 Fe^III 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 F<sub>1</sub> hybrids obtained from `line 227/1 × Roza', particularly under intermediate Fe deficiency. The results indicate that Fe^III 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.     

Enzymatic responses of cucumber roots to different levels of Fe supply

Development of the coordinated response to decreasing Fe availability was studied in cucumber plants grown in nutrient solution (NS) over a range of Fe^III-EDTA concentrations (from 0.1 to 80 M). Physiological and biochemical parameters were evaluated in intact roots, root extracts and plasma membrane (pm) vesicles. Acidification of the NS was evident in plants grown at 1 M Fe^III-EDTA and inversely related to the external Fe concentration. Fe^III-EDTA reduction by intact roots was also gradually depressed by increasing Fe supply. The rate of net nitrate uptake by the roots was directly related to the amount of Fe^III-EDTA added to the NS. Activity of pmH⁺-ATPase was significantly higher in plants grown without added Fe as compared to those grown at 80 M Fe. A lower increase, dependent on Fe concentration, was observed at 0.1, 1, 5 or 10 M Fe^III-EDTA. Activity of pmFe^III-EDTA reductase was also increased by Fe deprivation and strongly correlated with pmH⁺-ATPase activity. PEP-carboxylase activity gradually increased with decreasing Fe concentration in the NS. Changes in activity and amount of the enzyme showed a close correlation with parameters measured in intact roots (nitrate uptake, Fe^III-EDTA reduction). Results show that the development of the Fe-deficiency response in cucumber roots can be finely tuned by the level of Fe supply. Adjustments to different levels of available Fe involve a correlated modulation of pm-associated enzymes. PEP-carboxylase activity appeared to be a suitable metabolic marker of the Fe nutritional status of the plant.     

The effect of soil moisture on the tolerance of Lupinus pilosus genotypes to a calcareous soil

Commercial narrow-leafed lupins (Lupinus angustifolius L.) grown on calcareous soils commonly display chlorotic symptoms resembling Fe deficiency. The severity of chlorosis increases with concurrent increases in soil moisture content. Our research has indicated that the rough-seeded lupin species, Lupinus pilosus Murr., has a range of adaptation to calcareous soils, from tolerant to intolerant. A pot experiment was conducted comparing a tolerant, a moderately tolerant and a moderately intolerant genotype of L. pilosus. Plants were grown for 35 days in a calcareous soil (50% CaCO₃) at three moisture contents (80%, 100% and 120% of field capacity); the growth was compared with that on a fertile black cracking clay control soil at 70% of field capacity. Visual chlorosis score, chlorophyll meter readings, number of leaves and shoot dry weights were recorded at 14, 21, 28 and 35 days after sowing. Concentrations of chlorophyll, active Fe and nutrients in the youngest fully expanded leaves were also measured. Results showed that increased soil moisture increased the severity of chlorotic symptoms (increased chlorosis score) in all genotypes. The tolerant genotype showed significantly less symptoms than other genotypes at all moisture contents. All genotypes were able to recover from chlorosis symptoms at 80% moisture in the calcareous soil. Chlorosis score negatively correlated with chlorophyll meter readings, chlorophyll concentration and foliar active and total Fe, and Mn concentrations. Visual chlorosis score appeared to be a cost effective, accurate and efficient method enabling classification of the tolerance of genotypes. The chlorotic symptoms were likely to be due to HCO₃ ^- induced nutrient deficiencies or a direct effect of HCO₃ ^- on chlorophyll synthesis. This study indicates that the most probable mechanism of tolerance is related to an ability to prevent uptake of HCO₃ ^- or efficiently sequester it once inside the root which prevents increases in internal pH and transport to the shoots.     

Effects of sulphur nutrition on growth and nitrogen fixation of pea (Pisum sativum L.)

A S-deficient soil was used in pot experiments to investigate the effects of S addition on growth and N₂-fixation in pea (Pisum sativum L.). Addition of 100 mg S pot⁻¹ increased seed yield by more than 2-fold. Numbers of pods formed were the most sensitive yield component affected by S deficiency. Sulphur addition also increased the concentration of N in leaves and stems, and the total content of N in the shoots. The amounts of N fixed by pea were determined at four growth stages from stem elongation to maturity, using the ¹⁵N dilution technique. Sulphur addition doubled the amount of N fixed at all growth stages. In contrast, leaf chlorophyll content and shoot dry weight were increased significantly by S addition only after the flowering and pod fill stage, respectively. Pea roots were found to have high concentrations of S, reaching approximately 10 mg g⁻¹ dry weight and being 2.6–4.4 times the S concentration in the shoots under S-sufficient conditions. These results suggest that roots/nodules of pea have a high demand for S, and that N₂-fixation is very sensitive to S deficiency. The effects of S deficiency on pea growth were likely to be caused by the shortage of N, due to decreased N₂-fixation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Spectral response of rice (Oryza sativa L.) leaves to Fe2+ stress

In the management of lake eutrophication, the regulation effect of Fe is considered, in addition to the controlling nitrogen- and phosphorus input. Based on the “Fe hypothesis”, this paper tentatively ap-plied plant spectral response to the remote sensing early-warning mechanism of lake eutrophication. A laboratory water culture experiment with rice (Oryza sativa L.) was conducted to study Fe uptake by plants and the chlorophyll concentration and visible-near infrared spectrum of vegetable leaves as well as their interrelations under Fe²⁺ stress. Three spectral indices, i.e., A₁ (integral value of the changes of spectral reflectivity in the range 460―670 nm under Fe²⁺ stress), A₂ (integral value of the changes of spectral reflectivity in the range of 760―1000 nm under Fe²⁺ stress) and S (blue-shift range of red edge curve under Fe²⁺ stress), were used to establish quantitative models about the relationships between the rice leaf spectrum and Fe²⁺ stress. With the increase of Fe²⁺ in a culture solution, the Fe content in rice plants increased, while the chlorophyll concentration in vegetative leaves decreased. The spectral reflectivity of vegetable leaves increased in the visible light band but decreased in the near infrared band, and the blue-shift range of the red edge curve increased. The indices _A1, A₂ and S all had sig-nificant correlations with the Fe content in rice leaves, the correlation coefficient being respectively 0.951 (P < 0.01), −0.988 (P < 0.01) and 0.851 (P < 0.01), and simulated (multiple correlation coefficients R² > 0.96) and predict the Fe level in rice leaves.     

Toxic effects of Ni2+ on growth of cowpea (Vigna unguiculata)

Despite the importance of Ni-polluted soils throughout the world, comparatively little is known about the activity of Ni²⁺ required to reduce plant growth and the effects that Ni²⁺ toxicity has on the plant. Cowpea (Vigna unguiculata (L.) Walp. cv Caloona) was grown in dilute nutrient solutions to investigate the effect of Ni²⁺ activity on shoot and root growth. A Ni²⁺ activity of 1.4 μM was found to cause a 10% reduction in the relative fresh mass of the root and shoots. The primary site of Ni²⁺ toxicity was the shoots, with the younger leaves displaying an interveinal chlorosis (possibly a Ni-induced Fe deficiency) at Ni²⁺ activities ≥1.7 μM. Lateral root formation was inhibited in the two highest Ni²⁺ treatments (3.3 and 5.1 μM), and the roots growing at the highest Ni²⁺ activity were short and stubby and brown in color. However, no other symptoms of toxicity were observed on the roots at lower Ni²⁺ activities.     

Effect of bicarbonate on root growth and accumulation of organic acids in Zn-inefficient and Zn-efficient rice cultivars (Oryza sativa L.)

Bicarbonate has been regarded as a major factor for inducing Zn deficiency in lowland rice, but the mechanisms responsible for this effect are not yet fully understood. The objective of the present study was to test whether early effects of bicarbonate (HCO₃ ⁻)are inhibition of root growth due to the accumulation of organic acids induced by HCO₃ ⁻. Solution culture experiments were conducted using two rice cultivars differing in susceptibility to Zn deficiency, and four bicarbonate concentrations (0, 5, 10, 20 mM). Bicarbonate (5–20 mM) strongly inhibited root growth of the Zn-inefficient cultivar within 4 days of treatments. In contrast, root growth of the Zn-efficient cultivar was slightly stimulated with bicarbonate at 5–10 mM and not affected at 20 mM. The inhibitory effect of bicarbonate on root growth in the Zn-inefficient cultivar was mainly that of impairment of new root initiation rather than suppression of elongation of individual roots. Bicarbonate (5–20 mM) increased the concentrations of malate, succinate and citrate in the roots of both cultivars, but to a greater extent for the Zn-inefficient than for the Zn-efficient cultivars. The results suggest that the impairment of root growth was likely to be the initial action of bicarbonate in inducing Zn deficiency in lowland rice, and the inhibitory effect of bicarbonate on root growth of the Zn-inefficient cultivar might result from high accumulation and an insufficient compartmentation of organic acids in the root cells.     

Nitrogen and phosphorus cycling in relation to stand age of Eucalyptus regnans F. Muell

Lupins, canola, ryegrass and wheat fertilized with Na₂ ³⁵SO₄ and either ¹⁵NH₄Cl or K¹⁵NO₃(N:S=10:1), were grown in the field in unconfined microplots, and the sources of N and S (fertilizer, soil, atmosphere, seed) in plant tops during crop development were estimated. Modelled estimates of the proportion of lupin N derived from the atmosphere, which were obtained independently of reference plants, were used to calculate the proportion of lupin N derived from the soil. Total uptake of N and S and uptake of labelled N and S increased during crop development. Total uptake of S by canola was higher than lupins, but labelled S uptake by lupins exceeded uptake by canola. The form of N applied had no effect on uptake of labelled and unlabelled forms of N or S. Ratios of labelled to unlabelled S and ratios of labelled to unlabelled N derived from soil sources decreased during growth, and were less for S than for N for each crop at each sampling time. Although ratios of labelled to unlabelled soil-derived N were similar between crops at 155, 176 and 190 days after sowing, ratios of labelled to unlabelled S for lupins were higher than for the reference crops and declined during this period. The ratios of labelled to unlabelled S in lupins and the reference plants therefore bore no relationship either to ratios of labelled to unlabelled soil-derived N in the plants, or to total S uptake by the plants. Therefore the hypothesis that equal ratios of labelled N to unlabelled soil-derived N in legumes (Rleg) and reference plants (Rref) would be indicated by equal ratios of labelled to unlabelled S was not supported by the data. The results therefore show that the accuracy of reference plant-derived values of Rleg cannot be evaluated by labelling with ³⁵S.     

Application of chelator-buffered nutrient solution technique in studies on zinc nutrition in rice plant (Oryza sativa L.)

It has been difficult to impose different degrees of Zn deficiency on Poaceae species in nutrient solution because most chelators which would control Zn to low activities also bind Fe³⁺ so strongly that Poaceae species cannot obtain adequate Fe. Recently, a method has been developed to provide buffered Fe²⁺ at levels adequate for rice using Ferrozine (FZ), and use of other chelators to buffer the other micronutrient cations. The use of Fe²⁺ buffered with FZ in nutrient solutions in which Zn is buffered with HEDTA or DTPA was evaluated for study of Zn deficiency in rice compared to a conventional nutrient solution technique. The results showed that growth of rice plants in FZ+HEDTA-buffered nutrient solution was similar to that in the conventional nutrient solution. Severe zinc deficiency symptoms were observed in 28-day-old rice seedlings cultured with HEDTA-buffered nutrient solution at Zn²⁺ activities < 10^-10.6 M. With increasing free Zn²⁺ activities, concentrations of Zn, Fe, Cu, and Mn in shoots and roots were quite similar for the FZ+HEDTA-buffered nutrient solution and the conventional nutrient solution techniques. The percentages of water soluble Zn, Fe, Cu and Mn in shoots with HEDTA-buffered nutrient solution were also similar to those with the conventional solution. However, with DTPA-buffered nutrient solution, the rice seedlings suffered severe Fe deficiency; adding more FeFZ₃ corrected the Fe-chlorosis but shifted microelement buffering. Further, much higher total Zn concentrations are required to provide adequate Zn²⁺ in DTPA-buffered solutions, and the contents of Mn and Cu in shoots and roots cultured with DTPA-buffered solutions were much higher than those with the conventional or HEDTA-buffered solutions. In conclusion, DTPA-buffered nutrient solutions are not suitable but the FZ/HEDTA-buffered nutrient solution technique can be used to evaluate genotypic differences in zinc efficiency in rice.     

Proton efflux and transfer cell formation as responses to Fe deficiency of soybean in nutrient solution culture

Hydroponically grown Hawkeye soybeans with N supplied as NO ₃ ^– did not show any measurable pH decrease of the nutrient solution during the first week of Fe deficiency as has been observed for other Fe-efficient dicotyledonous species. Only after prolonged Fe stress with no renewal of the nutrient solution could an unspecific pH reduction be measured as a consequence of a decrease in the NO ₃ ^– content of the solution. On the other hand, Fe stress induced H⁺ efflux could be localized at the root tip region by day foru of-Fe treatment when intact plants were transferred from the nutrient solution to agar medium containing the pH indicator dye bromocresol purple. However, the activity of this H⁺ pump obviously was too weak to neutralize HCO₃-ions simultaneously excreted from older root parts and to acidify the bulk nutrient solution. Thus no remobilization of iron precipitated on older parts of the roots occurred and the plants remained chlorotic.Electron microscopy of the H⁺ extruding zone revealed hypodermal transfer cells with wall protuberances surrounded by cytoplasm especially rich in mitochondria. No transfer cells occurred in the rhizodermis as seen in other Fe-efficient dicots. Some cortical cells also showed transfer cell features with wall protuberances in the intercellular spaces. Often wall ingrowths were surrounded by a periplasmic space which reduced the potential surface amplification of the plasma membrane. It is concluded that the weak capacity of Hawkeye soybeans for Fe stress-induced H⁺ extrusion correlates with their less intense wall labyrinth formation as compared with other dicotyledonous species with higher Fe efficiency.     

The first iron(III) complexes with cyclin-dependent kinase inhibitors: Magnetic, spectroscopic (IR, ES+ MS, NMR, Fe Mössbauer), theoretical, and biological activity studies

The first Fe^III complexes 1-6 with cyclin-dependent kinase (CDK) inhibitors of the type [Fe(L_n)Cl₃]·nH₂O (n = 0 for 1, 1 for 2, 2 for 3-6; L₁-L₆ = C2- and phenyl-substituted CDK inhibitors derived from 6-benzylamino-9-isopropylpurine), have been synthesized and characterized by elemental analysis, IR, ⁵⁷Fe Mössbauer, ¹H and ¹³C NMR, and ES+ mass spectroscopies, conductivity and magnetic susceptibility measurements, and thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The study revealed that the compounds are mononuclear, tetrahedral high-spin (S = 5/2) Fe^III complexes with an admixture of an S = 3/2 spin state originating probably from five-coordinated Fe^III ions either connecting with a bidentate coordination mode of the CDK inhibitor ligand or relating to the possibility that one crystal water molecule enters the coordination sphere of the central atom in a portion of molecules of the appropriate complex. Nearly spin-only value of the effective magnetic moment (5.82 μ_eff/μ_B) was determined for compound 1 due to absence of crystal water molecule(s) in the structure of the complex. Based on NMR data and DFT calculations, we assume that the appropriate organic ligand is coordinated to the Fe^III ion through the N7 atom of a purine moiety. The cytotoxicity of the complexes was tested in vitro against selected human cancer cell lines (G-361, HOS, K-562 and MCF-7) along with the ability to inhibit the CDK2/cyclinE kinase. The best cytotoxicity (IC₅₀: 4-23 μM) and inhibition activity (IC₅₀: 0.02-0.09 μM) results have been achieved in the case of complexes 2-4, and complexes 3, 4 and 6, respectively. In addition, the X-ray structure of 2-chloro-6-benzylamino-9-isopropylpurine, i.e. a precursor for the preparation of L₁, L₄ and L₅, is also described.     

Differences in responses to iron deficiency among various cultivars of mungbean (Vigna radiata (L.) Wilczek)

Ten mungbean cultivars were evaluated for their resistance to iron deficiency in view of chlorosis symptoms, plant growth and seed yield under field conditions on a calcareous soil in Thailand. The KPS2 cultivar was highly susceptible; the KPS1, PSU1 and Pag-asa 1 cultivars were somewhat susceptible; the VC1163B cultivar was moderately tolerant; the CN36, CN60, UT1 and CNM-I cultivars were tolerant; and the CNM8509B cultivar was very tolerant to iron deficiency. Foliar application of a solution of 5 g L^-1 ferrous sulphate was effective in correcting chlorosis that was induced by iron deficiency, and it enhanced both the growth and the yield of susceptible cultivars. Compared with the susceptible cultivar KPS2, the tolerant cultivar UT1 had a greater ability to lower the pH of the nutrient solution in response to iron deficiency. The root-associated Fe³⁺-reduction activity of UT1 that had been grown in -Fe medium was similar to that of the plants grown in +Fe medium when the acidification of the medium occurred. Acidification of the medium in response to iron deficiency might contribute to the efficient solubilization of iron from calcareous soils, and it related more closely to the resistance to iron deficiency than Fe³⁺ reduction by roots in mungbean cultivars.     

Involvement of sulphur nutrition in modulating iron deficiency responses in photosynthetic organelles of oilseed rape (Brassica napus L.)

The aim of this study was to characterize the roles of sulphur (S) nutrition in modulating the responses to iron (Fe) deficiency in the photosynthetic organelles of oilseed rape. Eight-week-old plants grown hydroponically were fed with S-sufficient or S-deprived solution with or without Fe^III–EDTA. Responses to four S and Fe combined treatments were analysed after 5 and 10 days. Leaf chlorosis was generated by either S- or Fe-deprivation, with a decrease in chlorophyll and carotenoid content. These negative effects were more severe in the absence of S. The expression of Fe²⁺ transporter (IRT1) and Fe(III) chelate reductase (FRO1) gene was induced for the first 5 days and decreased after 10 days in the S-deprived roots, but largely improved by S supply even in the absence of Fe. Lack of ferric chelate reducing activity in the Fe-deprived roots in the absence of S was largely improved by S supply. The activity of photosynthesis, RuBisCO and sucrose synthase was closely related to S status in leaves. Electron microscopic observation showed that the Fe-deficiency in the absence of S greatly resulted in a severe disorganisation of thylakoid lamellae with loss of grana. However, these impacts of Fe-deficiency were largely restored in the presence of S. The present results indicate that S nutrition has significant role in ameliorating the damages in photosynthetic apparatus caused by Fe-deficiency.     

Reduction of Fe(III), Mn(III), and Cu(II) chelates by roots of pea (Pisum sativum L.) or soybean (Glycine max)

Neither the reduction of Fe(III) to Fe(II) by roots nor its induction by Fe-deficiency are unique characteristics of the reductive activities of roots. We show that chelated Mn(III) or chelated Cu(II), as well as chelated Fe(III), may be reduced by Fe-stressed roots of pea (Pisum sativum L.). Deficiency of Fe stimulated the reduction of Fe(III)EDTA about 20-fold, the reduction of Mn(III)CDTA about 11-fold, the reduction of Cu(II)(BPDS)₂ about 5-fold, and the reduction of Fe(III)(CN)₆ by only about 50%. Not only are metals other than Fe reduced as part of the Fe-stress response, but deficiencies of metals other than Fe stimulate the reductive activity of roots. We show that depriving peas or soybeans (Glycine max) of Cu or Zn stimulates the reduction of Fe(III).     

Chlorosis correction and agronomic biofortification in field peas through foliar application of iron fertilizers under Fe deficiency

Effectiveness of different iron (Fe) foliar sprays for leaf chlorosis correction and grain Fe boosting was studied in field peas under Fe deficiency. No chlorophyll reduction was observed in Fe deficient plants treated with foliar sprays. EDDHA [ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid)] followed by FeSO₄ (73.7?mg/l Fe) treated at the start of flowering was most responsive in correcting chlorosis and increasing shoot dry biomass in peas. Inductively coupled plasma-atomic emission spectroscopy data showed significant increase of Fe in grains while treated with all foliar sprays at the time of grain filling in Fe-deficient plants. Among them, FeSO₄ (73.7?mg/l Fe) was the most efficient in biofortifying Fe in mature grain under Fe deficiency in peas. Results also pinpoint that flowering is a suitable time for applying foliar sprays to boost Fe in mature grains. Taken together, application of Fe foliar sprays facilitated both chlorosis correction and Fe boosting in peas and can be further used by breeders and farmers.