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1.
Stimulation of root Fe(III) reductase activity by iron additions to iron-deficient growth media may be the result of iron activation of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase required for ethylene biosynthesis. Two different ethylene inhibitors, aminooxyacetic acid (AOA) (20 m; ACC synthase inhibitor) and cobalt (3 m CoCl2; ACC oxidase inhibitor), were used to study the effects of iron supply and cobalt inhibition on ethylene action in controlling the activity of Fe(III)-chelate reductase in pea (Pisum sativum L.) roots. Supplying 20 gm m Fe(III)-N,N-ethylenebis[2-(2-hydroxypheyl)-glycine [Fe(III)-EDDHA] to either cobalt-treated, iron-deficient Sparkle (normal parent) or E107 (brz mutant genotype) pea seedlings reversed the negative effects of cobalt on root Fe(III)-reductase activity. Re-supplying 20 m Fe(III)-EDDHA to iron-deficient, AOA-treated seedlings did not enhance root Fe(III)-reductase. Apparently, cobalt competes with iron for the active site in ACC oxidase during ethylene synthesis. Inhibition of root reductase activity by cobalt treatment lowered manganese, zinc, magnesium and potassium content of mutant E107 pea seedlings. In contrast, iron enhancement of root reductase activity in iron-deficient, cobalt-treated E107 seedlings resulted in higher seedling accumulations of manganese, zinc, magnesium and potassium. These results support the hypothesis that root cell plasma membrane reductase activity plays a role in cation uptake by root cells.  相似文献   

2.
Welch  Ross M.  Norvell  Wendell A.  Gesuwan  Patee  Schaefer  Steven 《Plant and Soil》1997,196(2):229-232
All phytometallophores are derived from methionine through S-adenosylmethionine (SAM) via nicotianamine. Ethylene is synthesized from methionine via SAM and 1-aminocyclopropane-1-carboxylic acid (ACC). This close similarity in biochemical pathways suggests that root-ethylene may play a role in regulating Fe(III)-phytometallophore homeostasis in cereal (Strategy II species) roots as well as in the regulation of Fe(III)-chelate reductase activity in Strategy I species. Barley (Hordeum vulgare L.) seedlings were grown in chelate-buffered nutrient solutions with increasing levels of Fe (i.e., 5, 25 or 100 µM Fe) as Fe(III)-HEDTA. Seedlings at each level of Fe were treated with either an inhibitor or a promoter of ethylene action. Treatment with the promoter, ACC (1 µM), had no significant effect of phytometallophore root efflux or Fe uptake by 19-d-old barley seedlings at all Fe levels. However, treatment with the inhibitor, aminooxyacetic acid (AOA, 10 µM) repressed the ability of cereal roots to absorb sufficient Fe to meet metabolic needs, but surprisingly enhanced phytometallophore root efflux rates at all Fe(III)-HEDTA levels. These results support a possible role of root-ethylene in Fe(III) uptake in cereals, but the mechanism remains unclear.  相似文献   

3.
The aim of this work was to clarify the role of S supply in the development of the response to Fe depletion in Strategy I plants. In S-sufficient plants, Fe-deficiency caused an increase in the Fe(III)-chelate reductase activity, 59Fe uptake rate and ethylene production at root level. This response was associated with increased expression of LeFRO1 [Fe(III)-chelate reductase] and LeIRT1 (Fe2+ transporter) genes. Instead, when S-deficient plants were transferred to a Fe-free solution, no induction of Fe(III)-chelate reductase activity and ethylene production was observed. The same held true for LeFRO1 gene expression, while the increase in 59Fe2+ uptake rate and LeIRT1 gene over-expression were limited. Sulphur deficiency caused a decrease in total sulphur and thiol content; a concomitant increase in 35SO4 2− uptake rate was observed, this behaviour being particularly evident in Fe-deficient plants. Sulphur deficiency also virtually abolished expression of the nicotianamine synthase gene (LeNAS), independently of the Fe growth conditions. Sulphur deficiency alone also caused a decrease in Fe content in tomato leaves and an increase in root ethylene production; however, these events were not associated with either increased Fe(III)-chelate reductase activity, higher rates of 59Fe uptake or over-expression of either LeFRO1 or LeIRT1 genes. Results show that S deficiency could limit the capacity of tomato plants to cope with Fe-shortage by preventing the induction of the Fe(III)-chelate reductase and limiting the activity and expression of the Fe2+ transporter. Furthermore, the results support the idea that ethylene alone cannot trigger specific Fe-deficiency physiological responses in a Strategy I plant, such as tomato.  相似文献   

4.
Summary Dicotyledonous plants respond to Fe deficiency by enhancing the capacity of their roots to reduce Fe(III) to Fe(II). It has been suggested that there are two different ferric redox systems in the roots: the standard reductase, active with ferricyanide and not inducible by Fe deficiency, and the turbo reductase, active with both ferricyanide and ferric chelates and inducible by Fe deficiency. We have used different experimental approaches to test whether or not the Fe(III)-reducing capacity of cucumber (Cucumis sativus L. cv. Ashley) roots can be explained by considering the standard and the turbo reductase as the same enzyme. For this, we used both Fe-sufficient and Fe-deficient plants, which were treated with ethylene inhibitors (cobalt or silver thiosulfate; found to inhibit the turbo reductase in a previous work), a protein synthesis inhibitor (cycloheximide), or an mRNA polyadenylation inhibitor (cordycepin). At different times after application of these inhibitors, reduction of both ferricyanide and Fe(III)-EDTA were determined. In addition, we studied the effects of pH and temperature on the reduction of ferricyanide and Fe(III)-EDTA by both Fe-sufficient and Fe-deficient plants. Results suggest that there are, at least, two different ferric redox systems in the roots. Enhancement of Fe(III)-reducing capacity (turbo reductase) by Fe-deficient plants probably requires the de novo synthesis of a (or several) protein(s), which has a high turnover rate and whose expression is presumably regulated by ethylene.Abbreviations Ch-R ferric chelate reductase - CHM cycloheximide - CN-R ferricyanide reductase - EDDHA N,N-ethylene bis[2-(2-hydroxyphenyl)-glycine] - EDTA ethylenediamine-tetraacetic acid - Ferrozine 3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine - HEDTA N-hydroxyethylethylene-diaminetriacetic acid - STS silver thiosulfate  相似文献   

5.
There is increasing evidence that Cu deficiency can induce root reductase activity, but the ecological and physiological significance of this is unknown. This study compared the characteristics of root reductase activity induced by Cu deficiency with those induced by Fe deficiency in red clover (Trifolium pratenseL. cv. Kenland), a Fe-efficient plant. Effects of other nutritional stresses were also investigated for comparison. Compared with the effect of Fe deficiency, Cu deficiency induced only a moderate level of root reductase activity, while other nutrient stresses had no effect, or even inhibited the root reductases activity, especially in the case of Zn deficiency. Compared with Fe deficiency-induced Fe(III)-chelate reductase, Cu deficiency-induced reductase displayed a different pattern of induction. The activity of the Cu deficiency-induced reductase in intact plants increased with time; in decapitated plants it showed a distinct peak at a later stage of the treatment. The Fe concentration in the roots was significantly increased under Cu deficiency. Furthermore, the reductase activity was presented in the entire root system, contrary to what was observed for the Fe-deficiency-induced reductase activity, which was confined to the root apex. Cu deficiency did not increase proton extrusion from the roots, even when growth was significantly affected. The present results suggest that in red clover Cu deficiency induces a root reductase that is different from the reductase induced by Fe deficiency.  相似文献   

6.
We investigated the effects of Fe and Cu status of pea (Pisum sativum L.) seedlings on the regulation of the putative root plasma-membrane Fe(III)-chelate reductase that is involved in Fe(III)-chelate reduction and Fe2+ absorption in dicotyledons and nongraminaceous monocotyledons. Additionally, we investigated the ability of this reductase system to reduce Cu(II)-chelates as well as Fe(III)-chelates. Pea seedlings were grown in full nutrient solutions under control, -Fe, and -Cu conditions for up to 18 d. Iron(III) and Cu(II) reductase activity was visualized by placing roots in an agarose gel containing either Fe(III)-EDTA and the Fe(II) chelate, Na2bathophenanthrolinedisulfonic acid (BPDS), for Fe(III) reduction, or CuSO4, Na3citrate, and Na2-2,9-dimethyl-4,7-diphenyl-1, 10-phenanthrolinedisulfonic acid (BCDS) for Cu(II) reduction. Rates of root Fe(III) and Cu(II) reduction were determined via spectrophotometric assay of the Fe(II)-BPDS or the Cu(I)-BCDS chromophore. Reductase activity was induced or stimulated by either Fe deficiency or Cu depletion of the seedlings. Roots from both Fe-deficient and Cu-depleted plants were able to reduce exogenous Cu(II)-chelate as well as Fe(III)-chelate. When this reductase was induced by Fe deficiency, the accumulation of a number of mineral cations (i.e., Cu, Mn, Fe, Mg, and K) in leaves of pea seedlings was significantly increased. We suggest that, in addition to playing a critical role in Fe absorption, this plasma-membrane reductase system also plays a more general role in the regulation of cation absorption by root cells, possibly via the reduction of critical sulfhydryl groups in transport proteins involved in divalent-cation transport (divalent-cation channels?) across the root-cell plasmalemma.  相似文献   

7.
The pea (Pisum sativum L.) mutant, E107 (brz, brz) accumulated extremely high concentrations of Fe in its older leaves when grown in light rooms in either defined nutrient media or potting mix, or outdoors in soil. Leaf symptoms (bronze color and necrosis) were correlated with very high Fe concentrations. When E107 plants were grown in nutrient solutions supplied 10 μm Fe, as the Fe(III)-N,N′-ethylenebis[2-(2-hydroxyphenyl)glycine] chelate, their roots released higher concentrations of Fe(III) reducing substances to the nutrient media than did roots of the normal parent cv, `Sparkle.' Reciprocal grafting experiments demonstrated that the high concentrations of Fe in the shoot was controlled by the genotype of the root. In short-term 59Fe uptake studies, 15-day-old E107 seedlings exhibited higher rates of Fe absorption than did `Sparkle' seedlings under Fe-adequate growth conditions. Iron deficiency induced accelerated short-term Fe absorption rates in both mutant and normal genotypes. Iron-treated E107 roots also released larger amounts of both protons and Fe(III) reductants into their nutrient media than did iron-treated `Sparkle' roots. Furthermore, the mutant translocated proportionately more Fe to its shoot than did the parent regardless of Fe status.  相似文献   

8.
Excised tomato roots infected with Meloidogyne javanica produced ethylene at 3-6 times the rate of noninfected roots. This increase in ethylene production started 5 days after inoculation. Gall growth and ethylene production in infected roots were accelerated by 1-aminocyclopropane-1-carboxylic acid (ACC), indole acetic acid (IAA), and ethrel known as ethylene production stimulators. When inhibitors of ethylene production, like aminoethoxyvinylglycine (AVG) or aminoxyacetic acid (AOA), or inhibitors of ethylene action like silver thiosulfate (STS), were applied, gall growth and ethylene production were inhibited. Enhanced expansion of parenchymatous cells was observed in sections from nematode-induced galls and ethylene-treated roots. Lignification of xylem elements and fibers in the vascular cylinder was markedly inhibited in the gall, compared with noninfected root tissue. Because ethylene is known to induce cell expansion and to inhibit lignification, it is suggested that this plant hormone plays a major role in the development of M. javanica-induced galls. Ethylene affects gall size by enhancing parenchymatous tissue development and allows expansion of giant cells and the nematode body by reducing tissue lignification.  相似文献   

9.
Fe deficiency was imposed in Citrus sinensis L. cultivars Valencia and New Hall grafted on C. aurantium and Swingle citrumelo rootstocks by the absence of Fe (-Fe) or by the presence of bicarbonate in the Hoagland nutrient solution. In Fe-deprived leaves total and active Fe concentration, and peroxidase and catalase activities were decreased while the ratios carotenoids/chlorophylls, P/Fe, and K/Ca were increased. Fe(III) chelate reductase activity was induced in (-Fe)-treated roots whereas it was depressed in bicarbonate-treated roots.  相似文献   

10.
11.
Waters  Brian M.  Blevins  Dale G. 《Plant and Soil》2000,225(1-2):21-31
Dicots and non-graminaceous monocots have the ability to increase root iron(III) reducing capacity in response to iron (Fe) deficiency stress. In squash (Cucurbita pepo L.) seedlings, Fe(III) reducing capacity was quantified during early vegetative growth. When plants were grown in Fe-free solution, the Fe(III) reducing capacity was greatly elevated, reached peak activity on day 4, then declined through day 6. Root ethylene production exhibited a temporal pattern that closely matched that of Fe(III) reducing capacity through day 6. On the 7th day of Fe deficiency, cluster root morphology developed, which coincided with a sharp increase in the root Fe(III) reducing capacity, although ethylene production decreased. Localization of Fe(III) reducing capacity activity was observed during the onset of Fe deficiency and through the development of the root clusters. It was noted that localization shifted from an initial pattern which occurred along the main and primary lateral root axes, excluding the apex, to a final localization pattern in which the reductase appeared only on secondary laterals and cluster rootlets. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

12.
Nicotianamine chelates and transports micronutrient metal ions in plants. It has been speculated that nicotianamine is involved in seed loading with micronutrients. A tomato (Solanum lycopersicum) mutant (chloronerva) and a tobacco (Nicotiana tabacum) transgenic line have been utilized to analyze the effects of nicotianamine loss. These mutants showed early leaf chlorosis and had sterile flowers. Arabidopsis (Arabidopsis thaliana) has four NICOTIANAMINE SYNTHASE (NAS) genes. We constructed two quadruple nas mutants: one had full loss of NAS function, was sterile, and showed a chloronerva-like phenotype (nas4x-2); another mutant, with intermediate phenotype (nas4x-1), developed chlorotic leaves, which became severe upon transition from the vegetative to the reproductive phase and upon iron (Fe) deficiency. Residual nicotianamine levels were sufficient to sustain the life cycle. Therefore, the nas4x-1 mutant enabled us to study late nicotianamine functions. This mutant had no detectable nicotianamine in rosette leaves of the reproductive stage but low nicotianamine levels in vegetative rosette leaves and seeds. Fe accumulated in the rosette leaves, while less Fe was present in flowers and seeds. Leaves, roots, and flowers showed symptoms of Fe deficiency, whereas leaves also showed signs of sufficient Fe supply, as revealed by molecular-physiological analysis. The mutant was not able to fully mobilize Fe to sustain Fe supply of flowers and seeds in the normal way. Thus, nicotianamine is needed for correct supply of seeds with Fe. These results are fundamental for plant manipulation approaches to modify Fe homeostasis regulation through alterations of NAS genes.  相似文献   

13.
14.
Enhanced ethylene production and leaf epinasty are characteristic responses of tomato (Lycopersicon esculentum Mill.) to waterlogging. It has been proposed (Bradford, Yang 1980 Plant Physiol 65: 322-326) that this results from the synthesis of the immediate precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), in the waterlogged roots, its export in the transpiration stream to the shoot, and its rapid conversion to ethylene. Inhibitors of the ethylene biosynthetic pathway are available for further testing of this ACC transport hypothesis: aminooxyacetic acid (AOA) or aminoethoxyvinylglycine (AVG) block the synthesis of ACC, whereas CO2+ prevents its conversion to ethylene. AOA and AVG, supplied in the nutrient solution, were found to inhibit the synthesis and export of ACC from anaerobic roots, whereas Co2+ had no effect, as predicted from their respective sites of action. Transport of the inhibitors to the shoot was demonstrated by their ability to block wound ethylene synthesis in excised petioles. All three inhibitors reduced petiolar ethylene production and epinasty in anaerobically stressed tomato plants. With AOA and AVG, this was due to the prevention of ACC import from the roots as well as inhibition of ACC synthesis in the petioles. With Co2+, conversion of both root- and petiole-synthesized ACC to ethylene was blocked. Collectively, these data support the hypothesis that the export of ACC from low O2 roots to the shoot is an important factor in the ethylene physiology of waterlogged tomato plants.  相似文献   

15.
Norvell  W. A.  Welch  R. M.  Adams  M. L.  Kochian  L. V. 《Plant and Soil》1993,(1):123-126
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).  相似文献   

16.
Radermachera sinica L. is an ornamental plant with demonstrated sensitivity to ethylene-induced leaf abscission. In this study, we examine the relationship between abscisic acid (ABA) and ethylene in initiating the abscission response. Treatment with 1 l L\s-1 of ethylene, 1 mM 1-aminocyclopropane-1-carboxylic acid (ACC) or 1 mM ABA resulted in complete defoliation of leaf explants. Application of 0.125 mM silver thiosulfate (STS) inhibited ethylene- and ACC-induced abscission but had no effect on explants treated with ABA. The ABA-induced abscission was unaffected by treatment with aminoethoxyvinylglycine (AVG) or aminooxyacetic acid (AOA). Treatment of explants with 1 mM cobalt chloride (CoCl2) or 2000 l L\s-1 of norbornadiene (NBD) completely inhibited abscission in explants treated with 1 l L\s-1 ethylene or 1 mM ACC but they were only marginally effective in blocking ABA-induced abscission despite the lower level of endogenous ethylene. ABA appeared to increase the sensitivity of explants to ethylene. However, the evidence suggests that ABA may also function independent of ethylene to induce leaf abscission in R. sinica.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - AOA aminooxyacetic acid - AVG aminoethoxyvinylglycine - CoCl2 cobalt chloride - NBD norbornadiene - STS silver thiosulfate  相似文献   

17.
Reduction of Fe(III) to Fe(II) by Fe(III) chelate reductase is thought to be an obligatory step in iron uptake as well as the primary factor in making iron available for absorption by all plants except grasses. Fe(III) chelate reductase has also been suggested to play a more general role in the regulation of cation absorption. In order to experimentally address the importance of Fe(III) chelate reductase activity in the mineral nutrition of plants, three Arabidopsis thaliana mutants (frd1-1, frd1-2 and frd1-3), that do not show induction of Fe(III) chelate reductase activity under iron-deficient growth conditions, have been isolated and characterized. These mutants are still capable of acidifying the rhizosphere under iron-deficiency and accumulate more Zn and Mn in their shoots relative to wild-type plants regardless of iron status. frd1 mutants do not translocate radiolabeled iron to the shoots when roots are presented with a tightly chelated form of Fe(III). These results: (1) confirm that iron must be reduced before it can be transported, (2) show that Fe(III) reduction can be uncoupled from proton release, the other major iron-deficiency response, and (3) demonstrate that Fe(III) chelate reductase activity per se is not necessarily responsible for accumulation of cations previously observed in pea and tomato mutants with constitutively high levels of Fe(III) chelate reductase activity.  相似文献   

18.
Growth, lipid peroxidation, H2O2 produciton and the response of the antioxidant enzymes and metabolites of the ascorbate glutathione pathway to oxidative stress caused by two concentrations (50 and 100 µM) of Cr(III) and Cr(VI) was studied in 15 day old seedlings of sorghum (Sorghum bicolor (L.) Moench cv CO 27) after 10 days of treatment. Cr accumulation in sorghum plants was concentration and organ dependant. There was no significant growth retardation of plants under 50 µM Cr(III) stress. 100 µM Cr(VI) was most toxic of all the treatments in terms of root and leaf growth and oxidative stress. 50 µM Cr(VI) treated roots exhibited high significant increase in superoxide dismutase (SOD), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) (p < 0.01) and significant increases in catalse (CAT), ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) (p < 0.05). A high increase in ascorbic acid (AA) level was seen in roots of 50 µM Cr(VI) treated plants in comparison with control. Levels of reduced glutathione (GSH) showed a varied and complex response in all the treatments in both plant parts. GSH/GSSG ratio was not affected by Cr(III) treatment in leaves, in contrast, roots exhibited significant reduction in the ratio. Results indicate that GSH depletion increased sensitivity to oxidative stress (Cr(VI) roots and leaves and Cr(III) 100 µM roots) and AA in tandem with APX compensated for GSH depletion by acting directly on H2O2 and the mechanism of defensive response in roots as well as leaves varied in its degree and effectiveness due to the concentration dependant differences observed in translocation of the element itself, reactive oxygen species (ROS) generation and enzyme inhibition based on the oxidation state supplied to the plants.  相似文献   

19.
Xuexian Li  Chunjian Li 《Plant and Soil》2004,261(1-2):147-153
Most dicotyledonous species respond to Fe deficiency by developing some mechanisms known as Fe-deficiency responses. The role of ethylene in regulation of root ferric reductase activity of wild-type tomato (Lycopersicon esculentum L.) and its mutant Never ripe (Nr), bean (Phaseolus vulgaris L., cv. Bifeng 80-30), and cucumber (Cucumis sativus L., cv. Xintaimici) plants grown in nutrient solution without Fe supply was studied under controlled condition. The results show that: (i) the tomato mutant Nr, which is insensitive to ethylene, presented rapid increase in root ferric reductase activity after omitting Fe from the nutrient solution; (ii) the initial time for increase in root ferric reductase activity was earlier than that in ethylene production after onset of Fe deficiency in the three species; (iii) like cobalt (3 μM Co2+), an inhibitor for ethylene production, high concentration of zinc (50 μM Zn2+) and copper (5 μM Cu2+) also suppressed the increase in root ferric reductase activity of Fe-starved plants; (iv) under Fe-sufficient conditions, indol-3-butylric acid (IBA) stimulated root ferric reductase activity of cucumber and bean plants, and this stimulating effect could not be suppressed by aminoethoxyvinylglycine (AVG, an inhibitor for ethylene synthesis). These results suggested that ethylene might not be directly involved in the regulation of root ferric reductase activity of Fe-deficient dicotyledonous species.  相似文献   

20.
Low O2 conditions were obtained by flowing N2 through the solution in which the tomato plants (Lycopersicon esculentum Mill cv Heinz 1350) were growing. Time course experiments revealed that low O2 treatments stimulated 1-aminocyclopropane-1-carboxylate (ACC) synthase production in the roots and leaves. After the initiation of low O2 conditions, ACC synthase activity and ACC content in the roots increased and reached a peak after 12 and 20 hours, respectively. The conversion of ACC to ethylene in the roots was inhibited by low levels of O2, and ACC was apparently transported to the leaves where it was converted to ethylene. ACC synthase activity in the leaves was also stimulated by low O2 treatment to the roots, reaching a peak after 24 hours. ACC synthase levels were enhanced by cobalt chloride and aminooxyacetic acid (AOA), although they inhibited ethylene production. Cobalt chloride enhanced ACC synthase only in combination with low O2 conditions in the roots. Under aeration, AOA stimulated ACC synthase activity in both the roots and leaves. However, in combination with low O2 conditions, AOA caused a stimulation in ACC synthase activity in the leaves and no effect in the roots.  相似文献   

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