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PubMed1992

Chemical carcinogens and overnutrition in diet-related cancer.

The intake of known dietary carcinogens was compiled and the cancer risk was estimated on the basis of carcinogenic potencies in animals as derived from the Carcinogenic Potency Database by Gold and co-workers. The total cancer risk was compared with the number of cancer cases attributed by epidemiologists to dietary factors (one-third of all cancer cases, i.e. approximately 80,000 per one million lives). Except for alcohol, the known dietary carcinogens could not account for more than a few hundred cancer cases. This was seen both with the DNA-reactive carcinogens (heterocyclic aromatic amines, polycyclic aromatic hydrocarbons, N-nitroso compounds, estragole, aflatoxin B1, ethyl carbamate, to name the most important factors) as well as with those carcinogens which have not been shown to react with DNA (e.g. caffeic acid and the carcinogenic metals arsenic and cadmium). Residues and contaminants turned out to be negligible. Among the various possibilities to explain the discrepancy we investigated the role of overnutrition. Dietary restriction in animals is well known for its strong reducing effect on spontaneous tumor formation. These data can be used to derive a carcinogenic potency for excess macronutrients: the tumor incidence seen with the restricted animals is taken as a control value and the increased tumor incidence in the animals fed ad libitum is attributed to the additional feed intake. For excess standard diet in rats, a carcinogenic potency TD50 of 16 g/kg/day was deduced from a recent study. Overnutrition in Switzerland, estimated to be 5.5 kcal/kg/day, was converted to excess food (1.9 g/kg/day) and the cancer incidence was calculated. The result, 60,000 cancer cases per one million lives, is provocatively close to the number of cases not explained by the known dietary chemical carcinogens. Mechanistic studies will be required to test our hypothesis and investigate the role of different types of macronutrients in overnutrition.

Carcinogens↗
PubMed1994

Inhibitory effect of curcumin on xanthine dehydrogenase/oxidase induced by phorbol-12-myristate-13-acetate in NIH3T3 cells.

Treatment of NIH3T3 cells with the tumor promoter phorbol-12-myristate-13-acetate (PMA) results within 30 min in a 1.8-fold elevation of xanthine oxidase (XO) activity, an enzyme capable of generating reactive oxygen species such as superoxide and hydrogen peroxide. Simultaneous administration of 2 and 10 microM curcumin with 100 ng/ml PMA inhibits PMA-induced increases in XO activity measured 30 min later by 22.7% and 36.5%, respectively. The PMA-induced conversion of xanthine dehydrogenase (XD) to XO is reduced by curcumin to the basal level noted in untreated cells. Activity of XO is remarkably inhibited by curcumin in vitro, but not by its structurally related compounds caffeic acid, chlorogenic acid and ferulic acid. Based on these findings, induction of XO activity is deemed to be one of the major causative elements in PMA-mediated tumor promotion, and the major inhibitory mechanism of curcumin on PMA-induced increases in XD/XO enzyme activities is through direct inactivation at the protein level.

3T3 Cells↗
PubMed1997

Mechanism of action of dietary chemoprotective agents in rat liver: induction of phase I and II drug metabolizing enzymes and aflatoxin B1 metabolism.

A range of potential chemoprotective agents, most of them natural dietary constituents, has been examined for ability to modulate both phase I (cytochrome P450 1A1, 1A2, 2B1/2, 2C11, 2E1, 3A, 4A) and phase II drug metabolizing enzymes (glutathione S-transferases, in particular subunits Yc2 and P, aflatoxin B1-aldehyde reductase and quinone reductase) in rat liver. In addition to assays of total enzyme activity and Western blots for individual isozymes, the ability of microsomes to metabolize aflatoxin B1, and of cytosols to conjugate aflatoxin B1 (AFB1)-epoxide to GSH and to produce AFB1-dialcohol, were measured. Induction of gamma-glutamyl transpeptidase activity was examined by histochemistry. Differing patterns of induction were observed, reflecting differences in the control of expression of the individual enzymes studied. Of the compounds examined, butylated hydroxytoluene, ethoxyquin, indole-3-carbinol and phenethyl isothiocyanate were the most potent bifunctional agents (inducing both phase I and II activities). Oltipraz, while only weakly inducing CYP1A2 and 2B1/2, was a potent inducer of phase II enzymes. Caffeic acid, garlic oil, sinigrin and propyl gallate all showed some ability to induce phase II enzymes. 4-Methyl catechol, alpha-tocopherol and red wine decreased certain phase I enzyme activities, while inducing total GST activity. Butylated hydroxytoluene, ethoxyquin, garlic oil and indole-3-carbinol induced gamma glutamyltranspeptidase in periportal hepatocytes. Particularly because of their ability to induce the detoxifying activities of glutathione S-transferase Yc2 and aldehyde reductase, butylated hydroxytoluene, ethoxyquin, indole-3-carbinol, oltipraz, phenethyl isothiocyanate and sinigrin will be effective blocking agents in rodents, if administered prior to AFB1. While these studies indicate the relative contributions of phase I and II metabolism in the overall protective effect in rat, care should be taken that a similar balance is achieved in man, and that relevant enzymes or iso forms are induced.

Aflatoxin B1↗
PubMed2000

Plant phenolics decrease intestinal tumors in an animal model of familial adenomatous polyposis.

Epidemiological studies consistently indicate that consumption of fruits and vegetables lowers cancer risk in humans and suggest that certain dietary constituents may be effective in preventing colon cancer. Plant-derived phenolic compounds manifest many beneficial effects and can potentially inhibit several stages of carcinogenesis in vivo. In this study, we investigated the efficacy of several plant-derived phenolics, including caffeic acid phenethyl ester (CAPE), curcumin, quercetin and rutin, for the prevention of tumors in C57BL/6J-Min/+ (Min/+) mice. These animals bear a germline mutation in the Apc gene and spontaneously develop numerous intestinal adenomas by 15 weeks of age. At a dietary level of 0.15%, CAPE decreased tumor formation in Min/+ mice by 63%. Curcumin induced a similar tumor inhibition. Quercetin and rutin, however, both failed to alter tumor formation at dietary levels of 2%. Examination of intestinal tissue from the treated animals showed that tumor prevention by CAPE and curcumin was associated with increased enterocyte apoptosis and proliferation. CAPE and curcumin also decreased expression of the oncoprotein beta-catenin in the enterocytes of the Min/+ mouse, an observation previously associated with an antitumor effect. These data place the plant phenolics CAPE and curcumin among a growing list of anti-inflammatory agents that suppress Apc-associated intestinal carcinogenesis.

Adenomatous Polyposis Coli↗
PubMed2002

Different genetic alterations in rat forestomach tumors induced by genotoxic and non-genotoxic carcinogens.

Human beings are exposed to a multitude of carcinogens in their environment, and most cancers are considered to be chemically induced. Here we examined differences in genetic alterations in rat forestomach tumors induced by repeated exposure to a genotoxic carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or N-methylnitrosourethane (MNUR), and chronic treatment with a non-genotoxic carcinogen, butylated hydroxyanisole (BHA) or caffeic acid (CA). A total of 132, 6-week-old male F344 rats were employed. Forty rats were treated with MNNG by intragastric administration at a dose of 20 mg/kg body wt once a week for 32 weeks, and 20 rats received 20 p.p.m. MNUR in their drinking water for 48 weeks. Further groups of 20 animals were administered 2% BHA or 2% CA in the diet for 104 weeks. The remaining rats were maintained without any supplement as controls. Multiple forestomach tumors were observed in all rats of the MNNG-, MNUR-, BHA- and CA-treated groups. Histopathologically, MNUR- and CA-treated groups showed almost the same pattern. On polymerase chain reaction-single strand conformation polymorphism analysis, H-ras and p53 gene mutations were observed at high and relatively low frequencies, respectively, in forestomach tumors induced by MNNG and MNUR. Most H-ras gene mutations were G-->A transitions in codons 7 and 12 of exon 1. On the other hand, forestomach tumors due to the non-genotoxic carcinogens, BHA and CA, had almost no mutations of the H-ras and p53 genes. Moreover, relative overexpression of cyclin D1 and p53 was detected in forestomach tumors induced by the genotoxic carcinogens, while their non-genotoxic counterparts had a tendency to show low expression of those molecules. Mutations of the beta-catenin gene were not detected in any group. The present study demonstrates that rat forestomach tumors induced by genotoxic and non-genotoxic carcinogens have different underlying genetic alterations, even if their pathological features are similar.

Animals↗
PubMed2006

Binding investigation of human 5-lipoxygenase with its inhibitors by SPR technology correlating with molecular docking simulation.

The binding features of a series of 5-lipoxygenase (5-LOX) inhibitors (caffeic acid, NDGA, AA-861, CDC, esculetin, gossypol and phenidone) to human 5-LOX have been studied by using surface plasmon resonance biosensor (SPR) technology based Biacore 3000 and molecular docking simulation analyses. The SPR results showed that the equilibrium dissociation constant (KD) values evaluated by Biacore 3000 for the inhibitors showed a good correlation with its reported IC50, suggesting that SPR technology might be applicable as a direct assay method in screening new 5-LOX inhibitors at an early stage. In addition, the 3D structural model of 5-LOX was generated according to the crystal structure of rabbit reticulocyte 15-lipoxygenase, and the molecular docking simulation analyses revealed that the predicted binding free energies for the inhibitors correlated well with the KD values measured by SPR assay, which implies the correctness of the constructed 3D structural model of 5-LOX. This current work has potential for application in structure-based 5-LOX inhibitor discovery.

Amino Acid Sequence↗
PubMed2005

Boron deficiency and concentrations and composition of phenolic compounds in Olea europaea leaves: a combined growth chamber and field study.

Boron deficiency is the most frequent micronutrient disorder in olive (Olea spp.) orchards. We tested the hypothesis that plant boron status affects phenolic metabolism, which, in turn, influences several ecophysiological traits of olive (Olea europaea L.) trees, by studying the effects of boron deficiency on leaf phenolic compounds of olive in a growth chamber experiment (CE) and a field experiment (FE). In the CE, a semi-hydroponic system was used to control nutrient supply. Plants received complete nutrient solution containing either 23 (control) or 0 microM H3BO3 (boron-deficient treatment). In the FE, boron-deficient trees were chosen based on visible boron-deficiency symptoms and analysis of their leaf boron concentration. Boron deficiency caused significant accumulation of phenolic compounds in leaves of CE plants (1.7 to 5.8 times more, depending on leaf age), but not in leaves of FE plants. However, in both experiments, the concentration of an unidentified phenolic compound, with a UV-spectrum resembling that of caffeic acid, increased in response to boron deficiency (by a factor of 40 to 184 in the CE and by a factor of three in the FE). Regression analysis showed that the concentration of this compound was negatively correlated to leaf boron concentration, irrespective of growth conditions and treatment. We conclude that, under field conditions, boron deficiency may not be the only factor determining the concentration of total phenolics, but it may be responsible for the accumulation of a distinct phenolic metabolite in olive leaves.

Boron↗
PubMed2000

Differential vulnerability of primary cultured cholinergic neurons to nitric oxide excess.

Many neuronal nitric oxide synthase (nNOS)-expressing brain neurons, including some cholinergic populations, are resistant to disease or to certain forms of excitotoxicity. Vulnerability to NO excess of forebrain (medial septal/diagonal band; MS-ACh) and brainstem (pedunculopontine/laterodorsal tegmental nuclei; BS-ACh) cholinergic neurons was compared in E16-E18 primary rat brain cultures. MS-ACh cells were approximately 300-fold more sensitive to the NO donor S-nitro-N-acetyl-D,L-penicillamine (SNAP) than were BS-ACh cells. Most (69%) MS-ACh cells contained nuclear DNA fragments by 2 h after addition of SNAP, while only 21% BS-ACh cells were TUNEL-positive after NO excess. Depletion of glutathione content did not potentiate the effect of SNAP on MS-ACh cells, but sensitized BS-ACh cells to the NO donor. Caffeic acid, a putative NF-kappa B inhibitor, enhanced the toxicity of SNAP to cholinergic neurons in both preparations. Our experiments show that cholinergic neurons in mixed primary cultures from different brain regions possess biochemical differences with respect to their vulnerability to NO excess.

Acetylcholine↗
PubMed1992

Purification and Characterization of Polyphenol Oxidase from Glandular Trichomes of Solanum berthaultii.

Type A glandular trichomes of the wild potato (Solanum berthaultii Hawkes) entrap insects by rapidly polymerizing the trichome contents after breakage by insect contact. Polymerization of trichome exudate appears to be driven by a soluble polyphenol oxidase (PPO). PPO constitutes up to 70% of the protein in individually collected trichomes and reaches a concentration approaching 200 mum in these organs. Trichome PPO has been purified and shown to be a monomeric copper metalloprotein with an isoelectric point of 5.5, possessing only o-diphenol oxygen oxido-reductase activity, and is larger than most other reported PPOs, with relative molecular weight of 59,000. Chlorogenic and caffeic acid were the most readily oxidized of 14 phenolic substrates tested. Polyclonal antibodies raised against the relative molecular weight 59,000 S. berthaultii trichome PPO were used to show that S. tuberosum L. trichomes express low levels of a cross-reactive protein that lacks detectable PPO activity.

Journal Article↗
PubMed1995

Differential expression of two O-methyltransferases in lignin biosynthesis in Zinnia elegans.

Caffeic acid 3-O-methyltransferase (CAOMT) and caffeoyl-coenzyme A 3-O-methyltransferase (CCoAOMT) are involved in different methylation pathways in lignin biosynthesis. We previously showed that only the CCoAOMT was markedly induced during lignification in in vitro differentiating tracheary elements (TEs) of Zinnia elegans. To further examine the expression patterns of CAOMT in lignification, we isolated a cDNA clone for Zinnia CAOMT. RNA gel blot analysis showed that the expression of the CAOMT gene did not correlate well with lignification during in vitro TE differentiation from Zinnia-isolated mesophyll cells. Tissue-print hybridization showed that, in the young internodes, the CAOMT mRNA signal was much more evident in phloem fibers than in xylem, whereas the CCoAOMT mRNA signal was predominantly present in differentiating xylem regions. In the older internode, both the CAOMT and CCoAOMT mRNAs markedly accumulated in phloem fibers and differentiating xylem regions. Immunocytochemical localization showed that the CAOMT protein staining was much more evident in phloem fibers and xylem fibers than in xylem TEs. These results indicate that the expression of these two O-methyltransferases is differentially regulated during lignification in different cell types in Zinnia. We suggest that all the intermediates in the CAOMT-mediated methylation pathway might become substrates for the CCoAOMT-mediated methylation pathway after coenzyme A ligation when these two pathways occur in the same lignifying cell types.

Cells, Cultured↗
PubMed1998

Herbicide safener-binding protein of maize. Purification, cloning, and expression of an encoding cDNA.

Dichloroacetamide safeners protect maize (Zea mays L.) against injury from chloroacetanilide and thiocarbamate herbicides. Etiolated maize seedlings have a high-affinity cytosolic-binding site for the safener [3H](R,S)-3-dichloroacetyl-2,2,5-trimethyl-1, 3-oxazol-idine ([3H]Saf), and this safener-binding activity (SafBA) is competitively inhibited by the herbicides. The safener-binding protein (SafBP), purified to homogeneity, has a relative molecular weight of 39,000, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and an isoelectric point of 5.5. Antiserum raised against purified SafBP specifically recognizes a 39-kD protein in etiolated maize and sorghum (Sorghum bicolor L.), which have SafBA, but not in etiolated wheat (Triticum aestivum L.), oat (Avena sativa L.), barley (Hordeum vulgare L.), tobacco (Nicotiana tabacum L.), or Arabidopsis, which lack SafBA. SafBP is most abundant in the coleoptile and scarcest in the leaves, consistent with the distribution of SafBA. SBP1, a cDNA encoding SafBP, was cloned using polymerase chain reaction primers based on purified proteolytic peptides. Extracts of Escherichia coli cells expressing SBP1 have strong [3H]Saf binding, which, like binding to the native maize protein, is competitively inhibited by the safener dichlormid and the herbicides S-ethyl dipropylthiocarbamate, alachlor, and metolachlor. SBP1 is predicted to encode a phenolic O-methyltransferase, but SafBP does not O-methylate catechol or caffeic acid. The acquisition of its encoding gene opens experimental approaches for the evaluation of the role of SafBP in response to the relevant safeners and herbicides.

Amino Acid Sequence↗
PubMed1998

Suppression of O-methyltransferase gene by homologous sense transgene in quaking aspen causes red-brown wood phenotypes

Homologous sense suppression of a gene encoding lignin pathway caffeic acid O-methyltransferase (CAOMT) in the xylem of quaking aspen (Populus tremuloides Michx.) resulted in transgenic plants exhibiting novel phenotypes with either mottled or complete red-brown coloration in their woody stems. These phenotypes appeared in all independent transgenic lines regenerated with a sense CAOMT construct but were absent from all plants produced with antisense CAOMT. The CAOMT sense transgene expression was undetectable, and the endogenous CAOMT transcript levels and enzyme activity were reduced in the xylem of some transgenic lines. In contrast, the sense transgene conferred overexpression of CAOMT and significant CAOMT activity in all of the transgenic plants' leaves and sclerenchyma, where normally the expression of the endogenous CAOMT gene is negligible. Thus, our results support the notion that the occurrence of sense cosuppression depends on the degree of sequence homology and endogene expression. Furthermore, the suppression of CAOMT in the xylem resulted in the incorporation of a higher amount of coniferyl aldehyde residues into the lignin in the wood of the sense plants. Characterization of the lignins isolated from these transgenic plants revealed that a high amount of coniferyl aldehyde is the origin of the red-brown coloration-a phenotype correlated with CAOMT-deficient maize (Zea mays L.) brown-midrib mutants.

Journal Article↗
PubMed1998

Localized changes in peroxidase activity accompany hydrogen peroxide generation during the development of a nonhost hypersensitive reaction in lettuce

Peroxidase activity was characterized in lettuce (Lactuca sativa L.) leaf tissue. Changes in the activity and distribution of the enzyme were examined during the development of a nonhost hypersensitive reaction (HR) induced by Pseudomonas syringae (P. s.) pv phaseolicola and in response to an hrp mutant of the bacterium. Assays of activity in tissue extracts revealed pH optima of 4.5, 6.0, 5.5 to 6.0, and 6.0 to 6.5 for the substrates tetramethylbenzidine, guaiacol, caffeic acid, and chlorogenic acid, respectively. Inoculation with water or with wild-type or hrp mutant strains of P. s. pv phaseolicola caused an initial decline in total peroxidase activity; subsequent increases depended on the hydrogen donor used in the assay. Guaiacol peroxidase recovered more rapidly in tissues undergoing the HR, whereas changes in tetramethylbenzidine peroxidase were generally similar in the two interactions. In contrast, increases in chlorogenic acid peroxidase were significantly higher in tissues inoculated with the hrp mutant. During the HR, increased levels of Mn2+/2, 4-dichlorophenol-stimulated NADH and NADPH oxidase activities, characteristic of certain peroxidases, were found in intercellular fluids and closely matched the accumulation of H2O2 in the apoplast. Histochemical analysis of peroxidase distribution by electron microscopy revealed a striking, highly localized increase in activity within the endomembrane system and cell wall at the sites of bacterial attachment. However, no clear differences in peroxidase location were observed in tissue challenged by the wild-type strain or the hrp mutant. Our results highlight the significance of the subcellular control of oxidative reactions leading to the generation of reactive oxygen species, cell wall alterations, and the HR.

Journal Article↗
PubMed2000

Linear beta-1,3 glucans are elicitors of defense responses in tobacco.

Laminarin, a linear beta-1,3 glucan (mean degree of polymerization of 33) was extracted and purified from the brown alga Laminaria digitata. Its elicitor activity on tobacco (Nicotiana tabacum) was compared to that of oligogalacturonides with a mean degree of polymerization of 10. The two oligosaccharides were perceived by suspension-cultured cells as distinct chemical stimuli but triggered a similar and broad spectrum of defense responses. A dose of 200 microg mL(-1) laminarin or oligogalacturonides induced within a few minutes a 1.9-pH-units alkalinization of the extracellular medium and a transient release of H(2)O(2). After a few hours, a strong stimulation of Phe ammonia-lyase, caffeic acid O-methyltransferase, and lipoxygenase activities occurred, as well as accumulation of salicylic acid. Neither of the two oligosaccharides induced tissue damage or cell death nor did they induce accumulation of the typical tobacco phytoalexin capsidiol, in contrast with the effects of the proteinaceous elicitor beta-megaspermin. Structure activity studies with laminarin, laminarin oligomers, high molecular weight beta-1, 3-1,6 glucans from fungal cell walls, and the beta-1,6-1,3 heptaglucan showed that the elicitor effects observed in tobacco with beta-glucans are specific to linear beta-1,3 linkages, with laminaripentaose being the smallest elicitor-active structure. In accordance with its strong stimulating effect on defense responses in tobacco cells, infiltration of 200 microg mL(-1) laminarin in tobacco leaves triggered accumulation within 48 h of the four families of antimicrobial pathogenesis-related proteins investigated. Challenge of the laminarin-infiltrated leaves 5 d after treatment with the soft rot pathogen Erwinia carotovora subsp. carotovora resulted in a strong reduction of the infection when compared with water-treated leaves.

Cells, Cultured↗
PubMed1974

Activation of 4-hydroxycinnamate hydroxylase in extracts from sorghum.

Three types of activation of 4-hydroxycinnamate hydroxylase have been observed in extracts of Sorghum bicolor. One involves the elimination of a lag period either by increasing the enzyme concentration or by the addition of a catalytic amount of caffeic acid. Two involve increases after freezing of incubation mixtures containing both hydroxycinnamate and ascorbate, one being a rapid but short-lived increase that may be limited to the freeze-thaw period, the other a slower and more sustained effect on the maximum linear rate obtained during the incubation period after thawing.

Journal Article↗
PubMed1978

Regulation of Phytoalexin Synthesis in Jackbean Callus Cultures: Stimulation of Phenylalanine Ammonia-Lyase and o-Methyltransferase.

Jackbean, Canavalia ensiformis (L.), callus tissues synthesized the phytoalexin, medicarpin (3-hydroxy-9-methoxypterocarpan), when treated with spore suspensions of Pithomyces chartarum (Berk. and Curt.) M. B. Ellis, a nonpathogen of jackbean. Medicarpin was isolated from treated callus tissue and identified by its ultraviolet and mass spectra. The minimum spore concentration found to elicit medicarpin synthesis after 26 hours was 1 x 10(5) spores/ml; levels of medicarpin in callus tissue increased linearly up to 1 x 10(7) spores/ml, indicating that the recognition sites for presumed elicitors were not saturated. Medicarpin was first detected in callus treated with 1 x 10(7) spores/ml, 6 to 12 hours after application, and the concentration reached a maximum at 48 hours, slowly declining thereafter to 72 hours. In callus treated with 3.15 mm HgCl(2), medicarpin concentrations were also maximum by 48 hours. Phenylalanine ammonia-lyase (EC 4.3.1.5) activity increased 2-fold in spore-treated callus after 36 hours. Isoliquiritigenin, daidzein, and genistein o-methyltransferase (EC 2.1.1.6) activities were increased 3- to 4-fold in treated callus. Caffeic acid and naringenin were more efficient substrates for o-methyltransferase activity than the other flavonoids or apigenin, but there was no increase in these o-methyltransferase activities in spore-treated callus. The phytoalexin response in this callus tissue culture system compares well with natural plant systems and should be an excellent system for investigating regulation of phytoalexin synthesis.

Journal Article↗
PubMed1982

Distribution of Secondary Plant Metabolites and Their Biosynthetic Enzymes in Pea (Pisum sativum L.) Leaves : Anthocyanins and Flavonol Glycosides.

Leaves of a novel strain of peas (Pisum sativum L.) were used to determine the distribution of secondary metabolites and their biosynthetic enzymes. Leaf epidermal layers in this strain are easily separated from the parenchyma. Anthocyanins and flavonol glycosides were localized in epidermal vacuoles only. Among the biosynthetic enzymes studied, phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), S-adenosyl-1-methionine (SAM):caffeic acid and SAM:quercetin methyltransferases (o-dihydric phenol methyltransferase, EC 2.1.1.42) and a flavonoid 7-O-glucosyltransferase (EC 2.4.1.91) were chiefly localized in the parenchyma, whereas trans-cinnamate 4-monooxygenase (EC 1.14.13.11), hydroxycinnamate:CoA ligases (EC 6.2.1.12) and a flavonoid 3-O-glucosyltransferase (EC 2.4.1.91) were found mainly in the epidermis. Flavanone (chalcone) synthase activity was found only in the epidermis, whereas chalcone isomerase (EC 5.5.1.6) was evenly distributed in epidermal and parenchyma tissues.

Journal Article↗
PubMed1983

Mechanism of iron uptake by peanut plants : I. Fe reduction, chelate splitting, and release of phenolics.

Iron deficiency in peanuts (Arachis hypogeae L.) caused an increase in release of caffeic acid, a higher rate of Fe(III) reduction, and increased rates of both Fe(III) chelate splitting and iron uptake.Experiments on Fe(III) reduction by phenolics (in vitro experiments) and by roots of Fe-deficient peanuts exclude the direct involvement of released phenolics in Fe(III) reduction by roots: Fe(III) reduction by phenolics had a pH optimum higher than 8.0 and was strongly dependent on the concentration and the stability of the supplied Fe(III) chelates. In contrast, Fe(III) reduction by roots of Fe-deficient peanuts had a pH optimum of about 5.0 and was less dependent on the stability of the supplied Fe(III) chelates. Furthermore, the observed release of phenolics into nutrient solution would have to be at least 200 times higher to attain the reduction rates of roots of Fe-deficient peanuts. The results of these experiments support the idea of an enzymic reduction of Fe(III) on the plasmalemma of cortical cells of roots.

Journal Article↗