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  • 1
    Digitale Medien
    Digitale Medien
    Synthesis and proof-of-function of a [14C]-labelled form of the plant iron chelator nicotianamine using recombinant nicotianamine synthase from barley (2003)
    Oxford, UK : Munksgaard International Publishers
    Physiologia plantarum 118 (2003), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The amino acid nicotianamine (NA) is essential for micronutrient metabolism in plants. Lack of NA results in a chlorotic phenotype and oxidative stress, since NA is a chelator of iron and other metal nutrients. To investigate the precise cellular function of NA in micronutrient transport and homeostasis, a protocol for the production of [14C]-labelled NA was developed. Recombinant NA synthase was used to generate [14C]-NA from [14C]-S-adenosylmethionine. After purification by solid-phase ion exchange about 66% yield was achieved. The identity of the [14C]-NA with chemically synthesized NA was demonstrated by several independent methods, including two TLC systems, two HPLC systems and immuno-detection. Moreover, biological function was shown by complementation of the Lycopersicon esculentum mutant chloronerva that is free of NA due to a defect in NA synthase. Proof-of-function for the produced [14C]-NA as a suitable tool for transport studies was provided monitoring the distribution of [14C]-NA after feeding to tomato and Ricinus communis seedlings.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1034/j.1399-3054.2003.00128.x
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  • 2
    Digitale Medien
    Digitale Medien
    Phloem loading and transport characteristics of iron in interaction with plant-endogenous ligands in castor bean seedlings (1999)
    Copenhagen : Munksgaard
    Physiologia plantarum 106 (1999), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The concentration of iron within cells has to be precisely regulated because shortage as well as surplus may be precarious for the survival of the cell. The maintenance of iron homeostasis in shoot organs requires an efficient signalling of the leaf cells’ iron status to the uptake sites of the roots. This ‘iron signal’ may be transferred by the phloem. The handling of iron in the symplast and during phloem transport calls for mechanisms taking into account the specific physicochemical properties of this element.Seedlings of Ricinus communis were used as model plants to investigate characteristic features of phloem loading, and of speciation and valence of iron during transport in the sieve tubes. When the storage endosperm is removed from the cotyledons, phloem is loaded from the reserve pool of the mesophyll cells. In this situation, iron and the other micronutrients copper, manganese and zinc are loaded in a constant stoichiometric ratio of 1:1 to the endogenous complexor nicotianamine (NA). Application of the chelators 1,4-di(4-phenylsulphonate)-1,10-phenanthroline (BPDS) and ethylenediaminetetraacetic acid to the cotyledon apoplast did not decrease the loading rate of iron, indicating symplastic loading. Supply of ferrous ions in various concentrations to the apoplast revealed the existence of two loading systems. One of them is linearly dependent upon the concentration, and remained unsaturated up to an apoplastic concentration of 200 μM. The other one, whose activity steeply inclines already with a slight increase of the apoplastic concentration, is saturable at a supply of 100 μM. The loading of iron is slowed down with time depending on whether iron is supplied to the apoplast as a complex with NA or citrate instead of as free ferrous ions. This effect may be caused by competition of these chelators with an iron uptake receptor in the plasmalemma of the mesophyll cells. In spite of the close relationship between iron and NA during phloem loading, the Fe-NA complex seems not to be the predominant transport species in the sieve tubes. A molecule of much larger mass than NA probably serves as a transport vehicle, as concluded from microdialysis experiments. Only 4% of the total iron in the sieve tube exudate was found to exist as Fe(II) and about 45% as Fe(III). The residue of more than 50% was tightly bound and not accessible even in the presence of the reductant sodium dithionite and the chelator BPDS. The conclusions regarding the nature of the transport species and the results on the valence of iron in the sieve tubes were confirmed by calculations with the software programs GEOCHEM [Sposito G, Mattigod SV (1979) A computer program for calculating chemical equilibria in soil solutions and other natural water systems. Kearney Foundation of Soil Sci, Univ. of California, Riverside, CA] and PHREEQC [Parkhurst (1995) PHREEQC-A computer program for speciation, reaction-path, adjective-transport, and inverse geochemical calculations. US Geological Survey]. A model is outlined on the basis of the experimental findings on the fate of iron from mobilisation in the endosperm to trans-chelation in the sieve tubes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1034/j.1399-3054.1999.106112.x
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  • 3
    Digitale Medien
    Digitale Medien
    Nicotianamine: mediator of transport of iron and heavy metals in the phloem? (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 88 (1993), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Recent work has demonstrated that minerals in plants are circulated between root and shoot. This occurs during the whole life time and renders possible response to changing environmental conditions. This mineral circulation occurs through intensive solute exchange between xylem and phloem in roots, stems, and leaves. The transport form of heavy metals such as iron, manganes, zinc and copper in the phloem, whether ionic or chelated, is unclear in most cases.The unusual amino acid nicotianamine (NA) is ubiquitous throughout the plant kingdom. It is a chelator of several divalent transition metals. Its physiological role was investigated with the tomato mutant chloronerva, the only known NA-free multicellular plant. The mutant also exhibits disturbances of its iron metabolism and that of other heavy metals. This leads, among others, to a typical intercostal chlorosis and progressive iron accumulation in the leaves. From the heavy metal chelating properties of NA and from the phenotype of the mutant chloronerva it is concluded that NA is needed for normal distribution of heavy metals in young growing tissues fed via the phloem. This function could be fulfilled by mediating phloem loading or unloading of heavy metals as well as by preventing their precipitation in the alkaline phloem sap. An attempt is made to explain the chloronerva phenotype in the light of the phloem transport hypothesis of chelated iron.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb01367.x
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  • 4
    Digitale Medien
    Digitale Medien
    Transport of metal micronutrients in the phloem of castor bean (Ricinus communis) seedlings (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 95 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The metal micronutrients (MN) copper, iron, manganese, and zinc are transported via the phloem in the course of remobilization and circulation. The extent of these processes and transport species are still largely unknown. The Ricinus seedling was used to study the transport of these metal micronutrients as well as their interactions with the plant-endogenous chelator nicotianamine (NA) by daily measurements of the concentrations in the seedling parts and in the sieve tube sap obtained from a cut at the hypocotyl hook.The concentrations of these micronutrients in the phloem exudate decreased slightly from day 4 to day 8 of seedling development. Maximum values at day 4 were 65 μM for Zn, 63 μM for Fe, 27 μM for Cu, and 12 μM for Mn. The phloem transport rates reached maxima of 0.12 nmol cm−2h−1 for Zn and Fe at days 6 and 7, corresponding to the maximum exudation rates. The magnitude of these transport rates were in agreement with the net translocation rates estimated by analyses of the concentrations in the individual seedling parts.The NA content of the seedlings increased from day 0 (seed before sowing) until day 8, from 16 nmol to 474 nmol, which corresponds to an average net synthesis rate of about 100 nmol day−1 between the days 4 and 8. The NA:MN ratio was constant at 0.5 in the seedlings within this period. The NA concentrations and the sum of the concentrations of all four micronutrients in the sieve tube sap showed a constant ratio of 1.25 over the entire experimental period. Thus, both complex partners were subject to a cotransport in the phloem.Removal of the supplying endosperm led to a decrease in MN and NA concentrations in the sieve tube sap to about 80% while an average excess of NA of 1.1 was maintained. Since the concentrations of other amino acids, also possible chelators of metal micronutrients, fall to about 10% after removal of the endosperm, their role seems to be negligible as vehicles of MN transport in the phloem. Thus it is suggested that the divalent micronutrients considered in this study are loaded and maybe transported as NA complexes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00821.x
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  • 5
    Digitale Medien
    Digitale Medien
    The nicotianamine molecule is made-to-measure for complexation of metal micronutrients in plants (1996)
    Springer
    BioMetals 9 (1996), S. 84-90 
    Details
    ISSN: 1572-8773
    Schlagwort(e): chelation ; metal complex stability ; metal micronutrients ; nicotianamine ; phloem transport
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract The non-proteinogenic amino acid nicotianamine (NA) is ubiquitous among plants. In meristematic tissues it reaches concentrations of about 400μmol (g fresh weight)−1. NA forms complexes, among others, with the metal micronutrients (MN) copper, zinc, iron and manganese (logK MeNA 18.6-8.8). Calculations of the dissociation curves of the metal-NA complexes based on the complex formation constants and on the acid dissociation constants of NA revealed their stability at the neutral or weak alkaline pH of cytoplasm and sieve tube sap. For the Mn-NA complex, dissociation begins at about pH 6.5, for all others dissociation occurs at more acid pHs. Thus, metal-NA complexes could theoretically persist also in the apoplasm and in xylem sap. The octanol water partition coefficient of NA is about 1 and those of its metal complexes are in the range of 0.3–0.4. The reason for this shift is perhaps the negative charge of the complexes. The higher lipophilicity of the free NA indicates that the NA supply to sites of requirement is faster than the removal of the complexes as long as membranes are an integral part of the transport paths. Changing phloem transport rates of MN-NA complexes by manipulation of the cotyledon apoplasm of Ricinus commuais L. suggest a competition of MN for NA at the site(s) of phloem loading. Thus, NA could control MN transport via phloem including recirculation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00188095
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  • 6
    Digitale Medien
    Digitale Medien
    Structure, expression and chromosomal localisation of the metallothionein-like gene family of tomato (1998)
    Springer
    Plant molecular biology 37 (1998), S. 701-714 
    Details
    ISSN: 1573-5028
    Schlagwort(e): gene family ; gene regulation ; heavy metals ; metallothionein ; oxidative stress
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Metallothioneins are small cysteine-rich proteins with strong binding capacity for heavy metals. In animals and fungi they are involved in cellular detoxification processes. Although genes for similar proteins exist in plants, less is known about the putative functions of their protein products. Here, we describe the characterisation of cDNAs specific for four genes (LEMT1, LEMT2, LEMT3 and LEMT4) encoding metallothionein-like proteins from tomato. Based on the characteristic cysteine pattern, the LEMT1, LEMT3 and LEMT4 gene products represent type 2 proteins. In contrast, the LEMT2 protein might establish a new structural pattern of metallothionein-like proteins not described before. Mapping experiments demonstrate that all four genes are localised at different genetic loci within the tomato genome. The members of the small gene family show a differential organ specific expression pattern. Expression of these genes is also influenced by heavy metals and by treatment with the thiol-oxidising drug diamide. We further describe the expression of the LEMT genes under different iron supply conditions both in tomato wild type as well as in the mutant chloronerva, which is defective in metal uptake regulation and exhibits a characteristic ‘apparent iron deficiency syndrome’.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006001701919
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  • 7
    Digitale Medien
    Digitale Medien
    Phloem translocation of Fe, Cu, Mn, and Zn in Ricinus seedlings in relation to the concentrations of nicotianamine, an endogenous chelator of divalent metal ions, in different seedling parts (1994)
    Springer
    Plant and soil 165 (1994), S. 181-188 
    Details
    ISSN: 1573-5036
    Schlagwort(e): micronutrients ; nicotianamine ; phloem transport ; Ricinus seedling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract During the first 8 days of germination the Ricinus seedling is supplied with all nutrients by the endosperm via phloem transport. In 4- to 8-days-old seedlings the concentrations and contents of Fe, Cu, Mn and Zn, and nicotianamine (NA) in the endosperm, cotyledons, hypocotyl and roots were estimated. From the data obtained translocation rates and flow profiles for the metals were established. The main sink for Fe, Mn and Zn were the cotyledons whereas Cu was mainly imported into the hypocotyl. Maximum flow rates occurred between days 5 and 7, for Zn between days 6 and 8. The time kinetics of NA and divalent metal ion concentrations and contents are interpreted as co-transport. The role of NA as transport vehicle of micronutrients in the sieve tubes is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00008060
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  • 8
    Digitale Medien
    Digitale Medien
    Iron-dependent changes of heavy metals, nicotianamine, and citrate in different plant organs and in the xylem exudate of two tomato genotypes. Nicotianamine as possible copper translocator (1994)
    Springer
    Plant and soil 165 (1994), S. 189-196 
    Details
    ISSN: 1573-5036
    Schlagwort(e): citrate ; copper transport ; heavy metals ; nicotianamine ; tomoto ; xylem exudate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The influence of Fe nutrition on the distribution of the heavy metals Fe, Mn, Zn, and Cu and of the heavy metal chelators nicotianamine (NA) and citrate in 6 different shoot and 3 different root parts and in xylem exudate of a NA-containing tomato wild type and its NA-less mutant was investigated. Under the same Fe supply the mutant showed higher Fe, Mn, and Zn concentrations in all organs investigated, with exception of the shoot apex. The Cu concentration in the mutant was only in root parts higher than in the wild type but much lower in leaves. Analyses of xylem exudate showed that Fe, Mn, and Zn were readily translocated by both genotypes from the roots to the shoot at all levels of Fe supply, whereas in the absence of NA, Cu was only poorly transported. Citrate as main Fe chelator in the xylem was present in high concentrations in xylem exudate of the wild type under low Fe supply but in the mutant also at 10 μM FeEDTA. NA occurred in xylem exudate of the wild type in concentrations high enough to chelate heavy metal ions. Generally, high Fe supply induced a decrease of Mn, Cu, and Zn concentrations in all organs of the wild type whereas high concentrations were observed in most cases under Fe deficiency. A positive correlation between Fe supply and NA concentration existed only in the shoot apex and in the xylem exudate of wild type plants. From the correlation between Cu and NA translocation and from the high stability constant of the NA-Cu-complex (log K=18.6) it is concluded that NA is a chelator for Cu in the xylem, whereas the translocation of Fe, Mn, and Zn is independent of NA.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00008061
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