Biosynthesis and secretion of mugineic acid family phytosiderophores in zinc-deficient barley

• Published in: The Plant journal : for cell and molecular biology 2006-10, Vol.48 (1), p.85-97
• Main Authors: Suzuki, Motofumi, Takahashi, Michiko, Tsukamoto, Takashi, Watanabe, Satoshi, Matsuhashi, Shinpei, Yazaki, Junshi, Kishimoto, Naoki, Kikuchi, Shoshi, Nakanishi, Hiromi, Mori, Satoshi, Nishizawa, Naoko K
• Format: Article
• Language: English
• Subjects: Azetidinecarboxylic Acid - analogs & derivatives; Azetidinecarboxylic Acid - chemistry; Azetidinecarboxylic Acid - metabolism; barley; Biological and medical sciences; Biological Transport; Botany; Chelating Agents - metabolism; Chromatography, High Pressure Liquid; Enzymes; Ferritins - genetics; Ferritins - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Profiling; Hordeum - genetics; Hordeum - growth & development; Hordeum - metabolism; Hordeum vulgare; Iron; Iron - analysis; Iron - metabolism; Metabolism; Metabolism. Physicochemical requirements; Methionine - chemistry; Methionine - metabolism; methionine salvage pathway; mugineic acid family phytosiderophores; Oligonucleotide Array Sequence Analysis; Plant physiology and development; Plant Roots - genetics; Plant Roots - growth & development; Plant Roots - metabolism; Plant Shoots - genetics; Plant Shoots - growth & development; Plant Shoots - metabolism; Positron-Emission Tomography; RNA, Messenger - metabolism; transport; Up-Regulation; Zinc; Zinc - analysis; Zinc - metabolism
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2006.02853.x

Mugineic acid family phytosiderophores (MAs) are metal chelators that are produced in graminaceous plants in response to iron (Fe) deficiency, but current evidence regarding secretion of MAs during zinc (Zn) deficiency is contradictory. Our studies using HPLC analysis showed that Zn deficiency induces the synthesis and secretion of MAs in barley plants. The levels of the HvNAS1, HvNAAT-A, HvNAAT-B, HvIDS2 and HvIDS3 transcripts, which encode the enzymes involved in the synthesis of MAs, were increased in Zn-deficient roots. Studies of the genes involved in the methionine cycle using microarray analysis showed that the transcripts of these genes were increased in both Zn-deficient and Fe-deficient barley roots, probably allowing the plant to meet its demand for methionine, a precursor in the synthesis of MAs. In addition, HvNAAT-B transcripts were detected in Zn-deficient shoots, but not in those that were deficient in Fe. Increased synthesis of MAs in Zn-deficient barley was not due to a deficiency of Fe, because Zn-deficient barley accumulated more Fe than did the control plants, ferritin transcripts were increased in Zn-deficient plants, and Zn deficiency promoted Fe transport from root to shoot. Moreover, analysis using the positron-emitting tracer imaging system (PETIS) confirmed that more ⁶²Zn(II)-MAs than ⁶²Zn²⁺ were absorbed by the roots of Zn-deficient barley plants. These data suggest that the increased biosynthesis and secretion of MAs arising from a shortage of Zn are not due to an induced Fe deficiency, and that secreted MAs are effective in absorbing Zn from the soil.