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1.
Nitrosoglutathione (GSNO) and β-cyclodextrin (β-CD) exhibit positive roles in regulating fruit quality. However, there are few reports about the effects of GSNO and β-CD on enhancing storability and boosting nitric oxide (NO), hydrogen sulfide (H 2S), and phenylpropane metabolism in fruits during storage. “Xintaihong” peach were treated with 0.5, 1.0, 1.5 mmol L −1 GSNO in 0.5% (w/v) β-CD solution (GSNO/β-CD). The effects of GSNO/β-CD on endogenous NO, H 2S, and phenylpropane metabolism were investigated. Treatment with GSNO/β-CD increased the color difference of peach and inhibited the increase of respiratory intensity, weight loss, and relative conductivity. Treatment with 1.0 mmol L −1 GSNO/β-CD increased the nitric oxide synthase (NOS-like) activity and L-arginine content, thereby promoting the accumulation of endogenous NO. By improving the activities of L-cysteine desulfhydrylase (L-CD), O-acetylserine sulfur lyase (OAS-TL), serine acetyltransferase (SAT), GSNO/β-CD increased the content of endogenous H 2S in peach. Treatment with GSNO/β-CD increased the activities of phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL), and cinnamic acid-4-hydroxylase (C4H), promoted the increase of total phenols, flavonoids, and lignin in peach. These results indicated that GSNO/β-CD treatment better maintained the quality of peach by improving the metabolism of endogenous NO, H 2S, and phenylpropane during storage. 相似文献
2.
Sodium Nitroprusside (SNP) and S-Nitrosoglutathione (GSNO) differently affect mitochondrial H 2O 2 release at Complex-I. mM SNP increases while GSNO decreases the release induced by succinate alone or added on top of NAD-linked
substrates. Stimulation likely depends on Nitric Oxide (
.
NO) (released by SNP but not by GSNO) inhibiting cytochrome oxidase and mitochondrial respiration. Preincubations with SNP
or high GSNO (10 mM plus DTE to increases its
.
NO release) induces an inhibition of the succinate dependent H 2O 2 production consistent with a
.
NO dependent covalent modification. However maximal inhibition of the succinate dependent H 2O 2 release is obtained in the presence of low GSNO (20–100 μM), but not with SNP. This inhibition appears independent of
.
NO release since μM GSNO does not affect mitochondrial respiration, or the H 2O 2 detection systems and its effect is very rapid. Inhibition may be partly due to an increased removal of O 2.− since GSNO chemically competes with NBT and cytochrome C in O 2.− detection. 相似文献
3.
Salinity impairs plant growth and development, thereby leading to low yield and inferior quality of crops. Nitric oxide (NO) has emerged as an essential signaling molecule that is involved in regulating various physiological and biochemical processes in plants. In this study, tomato seedlings of Lycopersicum esculentum L. “Micro-Tom” treated with 150 mM sodium chloride (NaCl) conducted decreased plant height, total root length, and leaf area by 25.43%, 24.87%, and 33.67%, respectively. While nitrosoglutathione (GSNO) pretreatment ameliorated salt toxicity in a dose-dependent manner and 10 µM GSNO exhibited the most significant mitigation effect. It increased the plant height, total root length, and leaf area of tomato seedlings, which was 31.44%, 20.56%, and 51.21% higher than NaCl treatment alone, respectively. However, NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide potassium (cPTIO) treatment reversed the positive effect of NO under salt stress, implying that NO is essential for the enhancement of salt tolerance. Additionally, NaCl?+?GSNO treatment effectively decreased O2? production and H2O2 content, increased the levels of soluble sugar, glycinebetaine, proline, and chlorophyll, and enhanced the activities of antioxidant enzymes and the content of antioxidants in tomato seedlings in comparison with NaCl treatment, whereas NaCl?+?cPTIO treatment significantly reversed the effect of NO under salt stress. Moreover, we found that GSNO treatment increased endogenous NO content, S-nitrosoglutathione reductase (GSNOR) activity, GSNOR expression and total S-nitrosylated level, and decreased S-nitrosothiol (SNO) content under salt stress, implicating that S-nitrosylation might be involved in NO-enhanced salt tolerance in tomatoes. Altogether, these results suggest that NO confers salt tolerance in tomato seedlings probably by the promotion of photosynthesis and osmotic balance, the enhancement of antioxidant capability and the increase of protein S-nitrosylation levels. 相似文献
4.
The effect of NO between cytochromes b and c of the mitochondrial respiratory chain were studied using submitochondrial particles (SMP) from bovine heart and GSNO and SPER-NO as NO sources. Succinate-cytochrome c reductase (complex II-III) activity (222±4 nmol/min. mg protein) was inhibited by 51% in the presence of 500 μM GSNO and by 48% in the presence of 30 μM SPER-NO, in both cases at ~1.25 μM NO. Neither GSNO nor SPER-NO were able to inhibit succinate-Q reductase activity (complex II; 220±9 nmol/min. mg protein), showing that NO affects complex III. Complex II-III activity was decreased (36%) when SMP were incubated with l-arginine and mtNOS cofactors, indicating that this effect is also produced by endogenous NO. GSNO (500 μM) reduced cytochrome b562 by 71%, in an [O 2] independent manner. Hyperbolic increases in O 2•- (up to 1.3±0.1 nmol/min. mg protein) and H 2O 2 (up to 0.64±0.05 nmol/min. mg protein) productions were observed with a maximal effect at 500 μM GSNO. The O 2•-/H 2O 2 ratio was 1.98 in accordance with the stoichiometry of the O 2•- disproportionation. Moreover, H 2O 2 production was increased by 72–74% when heart coupled mitochondria were exposed to 500 μM GSNO or 30 μM SPER-NO. SMP incubated in the presence of succinate showed an EPR signal ( g=1.99) compatible with a stable semiquinone. This EPR signal was increased not only by antimycin but also by GSNO and SPER-NO. These signals were not modified under N 2 atmosphere, indicating that they are not a consequence to the effect of NOx species on complex III area. These results show that NO interacts with ubiquinone-cytochrome b area producing antimycin-like effects. This behaviour comprises the inhibition of electron transfer, the interruption of the oxidation of cytochromes b, and the enhancement of [UQH •] ss which, in turn, leads to an increase in O 2•- and H 2O 2 mitochondrial production rates. 相似文献
5.
The effects of nitric oxide (NO) and/or iron (Fe) supplied to Fe deficient plants have been investigated in peanut ( Arachis hypogaea L.) grown in Hoagland nutrient solution with or without Fe. Two weeks after Fe deprivation, recovery was induced by addition of 250 μM sodium nitroprusside (SNP, a NO donor) and/or 50 μM Fe (Fe-EDTA) to the Fe deprived (-Fe) nutrient solution. Activities of antioxidant enzymes, leaf chlorophyll (Chl), and active Fe content decreased, whereas activities of H +-ATPase, ferric-chelate reductase (FCR), nitrate reductase, and nitric oxide synthase and NO production increased in Fe deficient plants, consequently an Fe chlorosis symptom appeared obviously. In contrast, these symptoms disappeared gradually after two weeks with NO and/or Fe supply, which caused an increases in leaf Chl and active Fe content, especially following by co-treatment with NO and Fe to values found in Fe sufficient plants. Increased activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and decreased accumulation of reactive oxygen species (H 2O 2, O 2 ?? ) and malondialdehyde enhanced the ability of resistance to oxidative stress. Supplied NO alone had the obvious effect on increased NO production and on activity of H +-ATPase and FCR, whereas root length and root/shoot ratio were most effectively increased by Fe supplied alone. Co-treatment with NO and Fe did the best effects on recovery peanut chlorosis symptoms by significantly increased Chl and available Fe content and adjusted distribution of Fe and other mineral elements (Ca, Mg, and Zn) in both leaves and roots. 相似文献
8.
Our previous results have demonstrated that both nitric oxide (NO) and hydrogen peroxide (H 2O 2) are involved in the promotion of adventitious root development in marigold ( Tagetes erecta L.). However, not much is known about the intricate molecular network of adventitious root development triggered by NO and
H 2O 2. In this study, the involvement of calcium (Ca 2+) and calmodulin (CaM) in NO- and H 2O 2-induced adventitious rooting in marigold was investigated. Exogenous Ca 2+ was capable of promoting adventitious rooting, with a maximal biological response at 50 μM CaCl 2. Ca 2+ chelators and CaM antagonists prevented NO- and H 2O 2-induced adventitious rooting, indicating that both endogenous Ca 2+ and CaM may play crucial roles in the adventitious rooting induced by NO and H 2O 2. NO and H 2O 2 treatments increased the endogenous content of Ca 2+ and CaM, suggesting that NO and H 2O 2 enhanced adventitious rooting by stimulating the endogenous Ca 2+ and CaM levels. Moreover, treatment with Ca 2+ enhanced the endogenous levels of NO and H 2O 2. Additionally, Ca 2+ might be involved as an upstream signaling molecule for CaM during NO- and H 2O 2-induced rooting. Altogether, the results suggest that both Ca 2+ and CaM are two downstream signaling molecules in adventitious rooting induced by NO and H 2O 2. 相似文献
9.
NO (nitric oxide) and H 2O 2 (hydrogen peroxide) are important signaling molecule in plants. Brassica napus L. was used to understand oligochitosan inducing production of NO (nitric oxide) and H 2O 2 (hydrogen peroxide) and their physiological function. The result showed that the production of NO and H 2O 2 in epidermal cells of B. napus L. was induced with oligochitosan by fluorescence microscope. And it was proved that there was an interaction between NO and H 2O 2 with L-NAME (N G-nitro- l-arg-methyl eater), which is an inhibitor of NOS (NO synthase) in mammalian cells that also inhibits plant NO synthesis, and CAT (catalase), which is an important H 2O 2 scavenger, respectively. It was found that NO and H 2O 2 induced by oligochitosan took part in inducing reduction in stomatal aperture and LEA protein gene expression of leaves of B. napus L. All these results showed that oligochitosan have potential activities of improving resistance to water stress. 相似文献
10.
NO和H 2O 2是参与植物抗非生物胁迫反应的重要信号分子, 为了确定NO和H 2O 2在大豆(Glycine max)根尖和根边缘细胞(root border cells, RBCs)耐铝反应中的作用及其相互关系, 以‘浙春3号’大豆为材料, 研究了铝毒胁迫下大豆根尖内源NO和H 2O 2的变化, 以及外源NO和H 2O 2诱导大豆根尖和RBCs的耐铝反应。结果表明, 50 μmol·L –1 Al处理48 h显著抑制大豆根的伸长, 提高Al在根尖的积累, 同时显著增加根尖内源NO和H 2O 2含量。施加0.25 mmol·L –1外源NO供体亚硝基铁氰化钠(Na 2[Fe(CN) 5NO]·2H 2O, sodium nitroprusside, SNP)和0.1 mmol·L –1H 2O 2, 能有效地缓解Al对大豆根伸长的抑制、根尖Al积累和RBCs 的死亡, 该缓解作用可以被0.05 mmol·L –1 NO清除剂2-(4- 羧基苯)-4,4,5,5- 四甲基咪唑-1- 氧-3- 氧化物, 钾盐(C 14H 16N 2O 4·K, carboxy-PTIO, cPTIO)和150 U·mL –1 H 2O 2清除酶(catalase, CAT)逆转。并且外源NO能够显著促进根尖H 2O 2的积累, 而外源H 2O 2对根尖NO的含量无显著影响。这表明NO和H 2O 2是诱导大豆根尖及RBCs耐铝反应的两种信号分子, NO可能通过调控H 2O 2的形成, 进而诱导大豆根尖及RBCs的耐铝反应。 相似文献
11.
In our study, one-month-old Melissa officinalis plants were subjected to Fe-deficiency treatments, such as 10 µM Fe (as direct iron deficiency, DD), and 30 µM Fe + 10 mM NaHCO 3 + 0.5 g l ?1 CaCO 3 (as indirect iron deficiency, ID), and 30 µM Fe (as control) for 14 d. Both Fe-deficiency types reduced plant growth, photosynthetic pigment contents, an active Fe content in roots and leaves, root Fe(III)-reducing capacity, Fe-use efficiency, maximal quantum yield of PSII photochemistry, a ratio of variable to basic fluorescence, and activities of antioxidant enzymes, while they increased lipid peroxidation and a H 2O 2 content in leaves. These effects were more pronounced in plants exposed to ID with bicarbonate than those of DD plants. We showed that sodium nitroprusside (SNP), as NO donor, could ameliorate the adverse effects of bicarbonate on above traits. The methylene blue, as NO blocker, reversed the protective effects conferred by SNP in the ID-treated plants as well as DD plants. These findings suggests that NO protects photosynthesis and growth of IDtreated plants as well as DD plants by contribution in availability and/or delivery of metabolically active iron or by changing activities of reactive oxygen species-scavenging enzymes. 相似文献
12.
Behavioral and pharmacological studies in insects have suggested that the nitric oxide (NO)/cyclic GMP (cGMP) signaling pathway is involved in the formation of long-term memory (LTM) associated with olfactory learning. However, the target molecules of NO and the downstream signaling pathway are still not known. In this study, we investigated the action of NO on single voltage-dependent Ca 2+ channels in the intrinsic neurons known as Kenyon cells within the mushroom body of the cricket brain, using the cell-attached configuration of the patch-clamp technique. Application of the NO donor S-nitrosoglutathione (GSNO) increased the open probability ( NPO) of single Ca 2+ channel currents. This GSNO-induced increase was blocked by ODQ, a soluble guanylate cyclase (sGC) inhibitor, suggesting that the NO generated by GSNO acts via sGC to raise cGMP levels. The membrane-permeable cGMP analog 8-Bro-cGMP also increased the NPO of single Ca 2+ channel currents. Pretreatment of cells with KT5823, a protein kinase G blocker, abolished the excitatory effect of GSNO. These results suggest that NO augments the activity of single Ca 2+ channels via the cGMP/PKG signaling pathway. To gain insight into the physiological role of NO, we examined the effect of GSNO on action potentials of Kenyon cells under current-clamp conditions. Application of GSNO increased the frequency of action potentials elicited by depolarizing current injections, indicating that NO acts as a modulator resulting in a stimulatory signal in Kenyon cells. We discuss the increased Ca 2+ influx through these Ca 2+ channels via the NO/cGMP signaling cascade in relation to the formation of olfactory LTM. 相似文献
13.
N-Nitrosodimethylamine (NDMA) in phosphate buffer was rapidly decomposed by Fenton reagent composed of H 2O 2, and Fe(II) ion. Electron spin resonance (ESR) studies using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) showed that characteristic four line 1:2:2:1 ESR signals due to the DMPO-OH adduct formed on treatment of DMPO with Fenton reagent disappeared in the presence of NDMA, and N-nitrosodiethylamine (NDEA), suggesting the interaction of the N-nitrosamines with Fenton reagent. Treatment of the N-nitrosamines with Fenton reagent generated nitric oxide (NO) as estimated by ESR technique using cysteine–Fe(II), and N-methyl-
-glucaminedithiocarbamate (MGD)–Fe(II) complexes. Characteristic 3, and single line signals due to 2 cysteine–Fe(II)–NO, and 2 cysteine–Fe(II)–2 NO complexes, respectively, and three line signals due to MGD–Fe(II)–NO were observed. Considerable amount of NO were liberated as determined by NO 2−, the final oxidation product of NO formed by reaction with dissolved oxygen in the aqueous medium. Spontaneous release of a small amount of NO from the N-nitrosamines was observed only on incubation in neutral buffers. Above results indicate that the N-nitrosamines were decomposed accompanying concomitant release of NO on contact with reactive oxygen species. 相似文献
14.
Immune cells kill invading microbes by producing reactive oxygen and nitrogen species, primarily hydrogen peroxide (H 2O 2) and nitric oxide (NO). We previously found that NO inhibits catalases in Escherichia coli, stabilizing H 2O 2 around treated cells and promoting catastrophic chromosome fragmentation via continuous Fenton reactions generating hydroxyl radicals. Indeed, H 2O 2-alone treatment kills catalase-deficient ( katEG) mutants similar to H 2O 2+NO treatment. However, the Fenton reaction, in addition to H 2O 2, requires Fe(II), which H 2O 2 excess instantly converts into Fenton-inert Fe(III). For continuous Fenton when H 2O 2 is stable, a supply of reduced iron becomes necessary. We show here that this supply is ensured by Fe(II) recruitment from ferritins and Fe(III) reduction by flavin reductase. Our observations also concur with NO-mediated respiration inhibition that drives Fe(III) reduction. We modeled this NO-mediated inhibition via inactivation of ndh and nuo respiratory enzymes responsible for the step of NADH oxidation, which results in increased NADH pools driving flavin reduction. We found that, like the katEG mutant, the ndh nuo double mutant is similarly sensitive to H 2O 2-alone and H 2O 2+NO treatments. Moreover, the quadruple katEG ndh nuo mutant lacking both catalases and efficient respiration was rapidly killed by H 2O 2-alone, but this killing was delayed by NO, rather than potentiated by it. Taken together, we conclude that NO boosts the levels of both H 2O 2 and Fe(II) Fenton reactants, making continuous hydroxyl-radical production feasible and resulting in irreparable oxidative damage to the chromosome. 相似文献
15.
Information on plant responses to combined ozone and cadmium stresses are scarce and limited to herbaceous species. In this research, two poplar clones (I-214 and Eridano), differently sensitive to O 3, were grown for 5 weeks in pots supplied with 0, 53.5, and 160.5 mg(Cd) kg ?1 (soil d.m.) and then exposed to 15-d O 3 fumigation (0.06 mm 3 dm ?3, 5 h a day). The effects of the two stressors, alone or in combination, on Cd, Ca, Fe, and Zn accumulation in above-nad below-ground organs, photosynthesis, leaf pigments, and accumulation of H 2O 2 and NO were investigated. Cadmium induced a reduction in stomatal conductance and a significant accumulation of H 2O 2 and NO in both clones nad negatively affected the carotenoid content in I-214. Ozone, on the other hand, counteracted Cd accumulation in the above-ground organs and significantly increased the xanthophyll de-epoxidation state indicating photoinhibition in O 3-treated plants. Surprisingly, O 3 alone or in combination with Cd decreased H 2O 2 accumulation in I-214. The NO production was generally stimulated by Cd, whereas it decreased following O 3 exposure in I-214. The overall data indicate that Cd and O 3 induced clone specific responses. Moreover, when they were applied in combination, antagonistic rather than synergistic effects were observed. 相似文献
16.
This study examined the effects of exogenous nitric oxide (NO) on physiological characteristics of peanut ( Arachis hypogaea L.) growing on calcareous soil. Sodium nitroprusside (SNP), a NO donor, was root application (directly; slow-release bag; slow-release capsule; slow-release particle) and foliar application. The results showed that SNP application alleviated iron (Fe) deficiency-induced chlorosis, increased the yield of peanut and increased the Fe concentration in peanut grain. SNP, especially supplied by slow-release particle improved the available Fe in soil by reducing pH of soil and increasing available Fe of soil. Furthermore, SNP application significantly increased the H +-ATPase and Fe 3+ reductase activities and increased the total Fe concentration in the leaves. Meanwhile, SNP application, especially foliar application enhanced the availability of Fe in the plant by significantly increasing the active Fe content and chlorophyll content in the leaves. In addition, SNP also increased the antioxidant activities, but decreased the superoxide anion (O 2??) generation rate and malondialdehyde content, which protected peanut against the Fe deficiency-induced oxidative stress. Therefore, these results support a physiological action of SNP on the availability, uptake and transport of Fe in the plant and foliar application SNP had the best effects in leaves and SNP supplied by slow-release particle had the best effects in roots. In addition, on the whole, the effects of SNP supplied by slow-release ways were better than directly supplied into the soil. 相似文献
17.
Iron (Fe) deficiency is a common agricultural problem that affects both the productivity and nutritional quality of plants. Thus, identifying the key factors involved in the tolerance of Fe deficiency is important. In the present study, the zir1 mutant, which is glutathione deficient, was found to be more sensitive to Fe deficiency than the wild type, and grew poorly in alkaline soil. Other glutathione‐deficient mutants also showed various degrees of sensitivity to Fe‐limited conditions. Interestingly, we found that the glutathione level was increased under Fe deficiency in the wild type. By contrast, blocking glutathione biosynthesis led to increased physiological sensitivity to Fe deficiency. On the other hand, overexpressing glutathione enhanced the tolerance to Fe deficiency. Under Fe‐limited conditions, glutathione‐deficient mutants, zir1, pad2 and cad2 accumulated lower levels of Fe than the wild type. The key genes involved in Fe uptake, including IRT1, FRO2 and FIT, are expressed at low levels in zir1; however, a split‐root experiment suggested that the systemic signals that govern the expression of Fe uptake‐related genes are still active in zir1. Furthermore, we found that zir1 had a lower accumulation of nitric oxide (NO) and NO reservoir S‐nitrosoglutathione (GSNO). Although NO is a signaling molecule involved in the induction of Fe uptake‐related genes during Fe deficiency, the NO‐mediated induction of Fe‐uptake genes is dependent on glutathione supply in the zir1 mutant. These results provide direct evidence that glutathione plays an essential role in Fe‐deficiency tolerance and NO‐mediated Fe‐deficiency signaling in Arabidopsis. 相似文献
18.
以"甘农三号"紫花苜蓿幼苗为材料,在水培条件下,研究了不同浓度镉(Cd)胁迫下紫花苜蓿根、茎和叶内源一氧化氮(NO)和活性氧(ROS)的生成机制以及根系活力的变化.结果表明:在0~2.0 mmol·L-1范围内,随着Cd浓度的增加,幼苗内NO含量呈现先升高后降低的趋势,最后可维持在略高或持平于对照的水平.幼苗内一氧化氮合成酶(NOS)活性、硝酸还原酶(NR)活性、亚硝酸根离子(NO2-)含量和类胡萝卜素(Car)含量的变化与NO含量变化规律相似却又不全相同.NOS和NR是影响幼苗茎中NO含量的主要因素,NOS、NO2-和NR则是影响叶中NO含量的主要因素,而根中NO含量主要与NOS活性和NO2-含量有较大相关性.随着Cd浓度的增加,幼苗内过氧化氢(H2 O2)含量、丙二醛(MDA)含量、超氧阴离子(O-2·)含量和相对电导率(REC)呈现显著升高趋势,说明高浓度的Cd处理会使ROS大量积累,细胞膜遭破坏,细胞质外流,进而引发膜脂过氧化.随着Cd浓度的增加,紫花苜蓿根系活力的变化为先升高后降低,指示了低浓度Cd处理会促进植物代谢,增强其生命力;而高浓度Cd会致使植株代谢受抑制,细胞受损害.NO和ROS的相关性不大,说明二者虽同为自由基,但它们产生和变化方式大有差别. 相似文献
19.
A study was carried out to assess the protective effects of exogenously applied nitric oxide (NO) in the form of its donor sodium nitroprusside (SNP) to strawberry seedlings ( Fragaria × ananassa cv. Camarosa) grown under iron deficiency (ID), salinity stress or combination of both. The experimental design contained control, 0.1 mM FeSO 4 (ID, Fe deficiency); 50 mM NaCl (S, Salinity) and ID + S. Plants were sprayed with 0.1 mM SNP or 0.1 mM sodium ferrocyanide, an analogue of SNP containing no NO. The deleterious effects of ID + S treatments on plant fresh and dry matters, total chlorophyll and chlorophyll fluorescence were more striking than those caused by the ID or S treatment alone. Furthermore, combination of salinity and iron stress exacerbated electrolyte leakage (EL) and the levels of malondialdehyde (MDA) and hydrogen peroxide (H 2O 2) in plant leaves compared to those in plants grown with either of the single stresses. NO treatment effectively reduced EL, MDA and H 2O 2 in plants grown under stress conditions applied singly or in combination. Salt stress alone and with ID reduced the superoxide dismutase (EC1.15.1.1) and catalase (EC 1.11.1.6) activities but increased that of POD (EC 1.17.1.7). Exogenously applied NO led to significant changes in antioxidant enzyme activities in either ID or S than those by ID+S. Overall, exogenously applied NO was more effective in mitigating the stress‐induced adverse effects on the strawberry plants exposed to a single stress than those due to the combination of both stresses. 相似文献
20.
This work was undertaken to verify whether surface NADH oxidases or peroxidases are involved in the apoplastic reduction of Fe(III). The reduction of Fe(III)-ADP, linked to NADH-dependent activity of horseradish peroxidase (HRP), protoplasts and cells of Acer pseudoplatanus, was measured as Fe(II)-bathophenanthrolinedisulfonate (BPDS) chelate formation. In the presence of BPDS in the incubation medium (method 1), NADH-dependent HRP activity was associated with a rapid Fe(III)-ADP reduction that was almost completely inhibited by superoxide dismutase (SOD), while catalase only slowed down the rate of reduction. A. pseudoplatanus protoplasts and cells reduced extracellular Fe(III)-ADP in the absence of exogenously supplied NADH. The addition of NADH stimulated the reduction. SOD and catalase only inhibited the NADH-dependent Fe(III)-ADP reduction. Mn(II), known for its ability to scavenge O ?2, inhibited both the independent and NADH-dependent Fe(III)-ADP reduction. The reductase activity of protoplasts and cells was also monitored in the absence of BPDS (method 2). The latter was added only at the end of the reaction to evaluate Fe(II) formed. Also, in this case, both preparations reduced Fe(III)-ADP. However, the addition of NADH did not stimulate Fe(III)-ADP reduction but, instead, lowered it. This may be related to a re-oxidation of Fe(II) by H 2O 2 that could also be produced during NADH-dependent peroxidase activity. Catalase and SOD made the Fe(III)-ADP reduction more efficient because, by removing H 2O 2 (catalase) or preventing H 2O 2 formation (SOD), they hindered the re-oxidation of Fe(II) not chelated by BPDS. As with the result obtained by method 1, Mn(II) inhibited Fe(III)-ADP reduction carried out in the presence or absence of NADH. The different effects of SOD and Mn(II), both scavengers of O ?2, may depend on the ability of Mn(II) to permeate the cells more easily than SOD. These results show that A. pseudoplatanus protoplasts and cells reduce extracellular Fe(III)-ADP. Exogenously supplied NADH induces an additional reduction of Fe(III) by the activity of NADH peroxidases of the plasmalemma or cell wall. However, the latter can also trigger the formation of H 2O 2 that, reacting with Fe(II) (not chelated by BPDS), generates hydroxyl radicals and converts Fe(II) to Fe(III) (Fenton's reaction). 相似文献
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