Article

Identification of Zn-nicotianamine and Fe-2'-Deoxymugineic acid in the phloem sap from rice plants (Oryza sativa L.).

Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, the University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657 Japan.
Plant and Cell Physiology (Impact Factor: 4.98). 01/2012; 53(2):381-90. DOI: 10.1093/pcp/pcr188
Source: PubMed

ABSTRACT In higher plants, the supply of metals such as Zn and Fe via phloem is important for the growth and physiology of young organs. However, little information is available on the speciation (chemical forms) of these metals in the phloem fluids. Because the pH of phloem fluids is slightly alkaline and the concentration of phosphate, which may bind to metals, is high, Zn and Fe in phloem fluids could be precipitated if these metals do not form complexes with some ligand compounds. In the present experiment, we examined the chemical forms of Zn and Fe in phloem sap collected from rice (Oryza sativa L.) by separating the phloem sap using size-exclusion and anion-exchange chromatography, and identifying the contents using electrospray ionization time-of-flight mass spectrometry. The low molecular weight chemical forms of Zn and Fe were identified as Zn-nicotianamine and Fe(III)-2'-deoxymugineic acid complexes, respectively. This report is the first to identify metal-chelate complexes in rice phloem sap.

0 Bookmarks
 · 
129 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mechanisms plants use to transport metals from roots to shoots are not completely understood. It has long been proposed that organic molecules participate in metal translocation within the plant. However, until recently the identity of the complexes involved in the long-distance transport of metals could only be inferred by using indirect methods, such as analyzing separately the concentrations of metals and putative ligands and then using in silico chemical speciation software to predict metal species. Molecular biology approaches also have provided a breadth of information about putative metal ligands and metal complexes occurring in plant fluids. The new advances in analytical techniques based on mass spectrometry and the increased use of synchrotron X-ray spectroscopy have allowed for the identification of some metal-ligand species in plant fluids such as the xylem and phloem saps. Also, some proteins present in plant fluids can bind metals and a few studies have explored this possibility. This study reviews the analytical challenges researchers have to face to understand long-distance metal transport in plants as well as the recent advances in the identification of the ligand and metal-ligand complexes in plant fluids.
    Frontiers in Plant Science 01/2014; 5:105. · 3.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An important goal of micronutrient biofortification is to enhance the amount of bioavailable zinc in the edible seed of cereals and more specifically in the endosperm. The picture is starting to emerge for how zinc is translocated from the soil through the mother plant to the developing seed. On this journey, zinc is transported from symplast to symplast via multiple apoplastic spaces. During each step, zinc is imported into a symplast before it is exported again. Cellular import and export of zinc requires passage through biological membranes, which makes membrane-bound transporters of zinc especially interesting as potential transport bottlenecks. Inside the cell, zinc can be imported into or exported out of organelles by other transporters. The function of several membrane proteins involved in the transport of zinc across the tonoplast, chloroplast or plasma membranes are currently known. These include members of the ZIP (ZRT-IRT-like Protein), and MTP (Metal Tolerance Protein) and heavy metal ATPase (HMA) families. An important player in the transport process is the ligand nicotianamine that binds zinc to increase its solubility in living cells and in this way buffers the intracellular zinc concentration.
    Frontiers in Plant Science 01/2014; 5:30. · 3.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Iron (Fe) is one of the most abundant elements on earth, but its limited bioavailability poses a major constraint for agriculture and constitutes a serious problem in human health. Due to an improved understanding of the mechanisms that control Fe homeostasis in plants, major advances toward engineering biofortified crops have been made during the past decade. Examples of successful biofortification strategies are, however, still scarce and the process of Fe loading into seeds is far from being well understood in most crop species. In particular in grains where the embryo represents the main storage compartment such as legumes, increasing the seed Fe content remains a challenging task. This review aims at placing the recently identified actors in Fe transport into the unsolved puzzle of grain filling, taking the differences of Fe distribution between various species into consideration. We summarize the current knowledge on Fe transport between symplasmic and apoplasmic compartments, and provide models for Fe trafficking and localization in different seed types that may help to develop high seed Fe germplasms.
    Frontiers in Plant Science 01/2014; 4:535. · 3.60 Impact Factor