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  • 1
    Electronic Resource
    Electronic Resource
    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
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb01367.x
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: micronutrients ; nicotianamine ; phloem transport ; Ricinus seedling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008060
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Keywords: citrate ; copper transport ; heavy metals ; nicotianamine ; tomoto ; xylem exudate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008061
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    Paper (German National Licenses)
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