Sei-ichi Takagi

Physiological aspect of mugineic acid, a possible phytosiderophore of graminaceous plants

Abstract A natural chelator designated mugineic acid (MA) was isolated from the root washings of barley cultivar “Minorimugi”;. The secretion of MA by barley roots occurred in the morning, and was much enhanced under Fe stress. MA enhanced the solubility of Fe(III) between pH 4 and 9. When added to nutrient solutions, MA strongly stimulated the uptake of Fe by “Fe‐inefficient”; rice seedlings. Commonly used chelating agents such as EDTA, EDDHA, citrate, etc. had no stimulative effects. The MA‐mediated Fe uptake proved to be dependent on metabolic energy. These results suggest the possibility of MA functioning as a phytosiderophore for graminaceous plants.

Naturally occurring iron-chelating compounds in oat- and rice-root washings: I. Activity Measurement and Preliminary Characterization

Abstract The root washings of water-cultured oat and rice (non-sterile) contained some sort of amphoteric, iron-solubilizing chelating (or complexing) compound(s), which could be separated into a “cationic fraction” by elution in a cation exchanger column with in NH4OH. In oats, the release of the chelator into the washings greatly increased under iron-stress conditions. Under the same condition “iron-inefficient” rice plants also increased the release of the chelator, though to a much less extent than did the oats. Further examination of the “cationic fraction” revealed that this chelator may be a heat-stable, acid-hydrolyzable non-marromolecule of extraordinarily high polarity. In the absence of interfering ions, the chelator was able to solubilize hydra ted Fe (III) oxide effectively within a range of pH 4 to 9. Its Fe-solubilizing action was inhibited by the presence of divalent metals, the extent being in the order, Cu>Cos≥Zn>Mn> Ca (no inhibition).

Dynamic state of mugineic acid and analogous phytosiderophores in Fe‐deficient barley

Abstract An HPLC method for MAs (mugineic acid and its analogues) analysis was established. By this method, time course change of MAs secreted from the roots of Fe‐deficient barley were traced. After about one week of ‐Fe treatment, MAs secreted from the roots gradually increased and after 40 days it became plateau. The several MAs were synchronously secreted from the roots throughout a day; their amounts were maximum at noon. The pattern of MAs secretion was different from that of amino acids. MAI was found to be trace in roots, xylem sap and shoots of the control (+Fe) plant. However, MAs concentrations remarkably increased in those tissues when Fe‐deficiency chlorosis progressed due to ‐Fe treatment. From experiments of 14CO2‐fixation by photosynthesis, 14C‐MA1 secreted from the roots was found to be biosynthesized with a half‐life of 24 h.

Studies on phytosiderophores: Biosynthesis of mugineic acid and 2′-deoxymugineic acid in Hordeum vulgare L. var. Minorimugi

Abstract The feeding study using L-[1- 13 C]methionine revealed that labelled carbons were incorporated into C-1, 4′, and 4″ of purified mugineic acid and 2′-deoxymugineic acid from their 13 C-NMR spectra.

Avenic acid, a new amino acid possessing an iron chelating activity

Abstract A new amino acid derivative possessing an iron chelating activity was isolated from root washings of water cultured Avena sativa under iron deficient conditions. The structure of this compound, avenic acid A has been determined as 2(S),3′(S),3″(S)-N-[3-(3-hydroxy-3-carboxypropylamino)-3-carboxypropyl]-homoserine (1) on the basis of chemical and spectroscopic evidence.

Incorporation of 15N and 14C of methionine into the mugineic acid family of phytosiderophores in iron-deficient barley roots

The role of methionine as a precursor in mugineic acid (MA) biosynthesis was studied by feeding 15 N-ammonium sulfate, 14 C-amino acids, and [1-14 C, 15 N]-methionine to iron-deficient barley roots (Hordeum vulgare L. cv. Minorimugi), grown hydroponically. The incorporation of isotopes into amino acids was also examined. Methionine appears to be the most efficient precursor of the mugineic acid family (MAs) of phytosiderophores; homoserine was also incorporated into the MAs, but other amino acids such as glutamate, alanine, and γ-amino butyric acid did not act as precursors of MAs. Carbon-14 and 15 N of methionine were incorporated into MAs. This specific incorporation of 14 C and 15 N indicated that the nitrogen atoms of MAs were derived from two molecules of methionine. It is suggested that deoxymugineic acid (DMA) is probably the first phytosiderophore to be synthesized on the biosynthetic pathway of MAs.

Co-occurrence of nicotianamine and avenic acids in Avena sativa and Oryza sativa

Abstract An amino acid derivative isolated from seedlings of Avena sativa and Oryza sativa , along with avenic acid A and its derivatives which possess a chelating ability with iron ions, has been shown to be nicotianamine. The co-occurrence of nicotianamine and avenic acids in the same plant, as well as their structural similarity, reveals their close biosynthetic relationship.

X-Ray crystal structure of the copper (II) complex of mugineic acid, a naturally occurring metal chelator of graminaceous plants

The X-ray crystal structure of the copper complex of mugineic acid shows that the ligant molecule co-ordinates with the copper ion in a hexadentate fashion, forming a distorted octahedral geometry.

Biosynthesis of avenic acid A in oat cv. Onward: studies with 14C or 15N labeled compounds

The precursory role of avenic acid A (AVA) in the biosynthesis of the mugineic acid family (MAs) of phytosiderophores was studied by feeding 14C or 15N labeled compounds into iron-deficient oat roots (Avena sativa L. cv. Onward). Carbon-14 of methionine was incorporated into AVA and 2′-deoxymugineic acid (DMA) in the oat roots, while 14C of homoserine was not incorporated into either AVA or DMA. The molar radioactivity of DMA was higher than that of AVA. Incorporation of 15N into MAs was examined by feeding 15N-ammonium sulfate into oat roots. The value of 15N atom-% excess of DMA was higher than that of AVA.These results indicate that methionine, rather than homoserine, is the direct precursor of MAs in oat, which is similar to that in barley, and that AVA is not the precursor of the other MAs.

Iron extraction efficacy of plant borne mugineic acid family phytosiderophores in indian calcareous soils

Abstract An experiment with different chelators involving plant made mugineic acid (MA), deferrioxamine B (FOB) and DTPA along with deionized water as a control was performed to evaluate the Fe extraction ability of the chelators from Indian calcareous soils having high pH, low Fe content, and rich in calcium carbonate. MA manifested the highest Fe extraction efficiency in all the calcareous soils. On the contrary, other chelators displayed rather poor activity of Fe extraction. MA also mobilized Cu, Zn, Mn, Ca, and Mg. However, DTPA solubilized Ca more efficiently than MA. Different calcareous soils also varied with respect to Fe extraction ability. In a green house experiment, Indian barley cultivar (cv) NDB‐209 under calcareous soils, however, exhibited very low Fe solubility in the soil rhizosphere indicating the possibility of simultaneous and periodical release and high Fe(III)‐MAs uptake rate by the plants in quick succession to optimize Fe acquisition efficiency and minimize the microbial decompos...