Senescence-induced iron mobilization in source leaves of barley (Hordeum vulgare) plants

• Published in: The New phytologist Vol. 195; no. 2; pp. 372 - 383
• Main Authors: Shi, Rongli, Weber, Günther, Köster, Jessica, Reza‐Hajirezaei, Mohammad, Zou, Chunqin, Zhang, Fusuo, von Wirén, Nicolaus
• Format: Journal Article
• Language: English
• Published: Oxford, UK New Phytologist Trust 01-07-2012; Blackwell Publishing Ltd; Wiley Subscription Services, Inc
• Subjects: Azetidinecarboxylic Acid - analogs & derivatives; Azetidinecarboxylic Acid - metabolism; Barley; Biological Transport - drug effects; Biosynthesis; Chelating agents; Chlorosis; Citrates; Citric acid; Citric Acid - metabolism; Crop harvesting; Darkness; deoxymugineic acid (DMA); Gene expression; Gene Expression Regulation, Plant - drug effects; Hordeum - drug effects; Hordeum - genetics; Hordeum - growth & development; Hordeum - metabolism; Hordeum vulgare; Hydroponics; Iron; Iron - metabolism; iron biofortification; iron chelates; Iron deficiency; iron efficiency; iron retranslocation; Leaves; Nicotianamine; nicotianamine synthase; Nitrogen; Nitrogen - deficiency; Nitrogen - metabolism; Nitrogen - pharmacology; nitrogen nutrition; Nutrient solutions; Phenotype; phloem transport; Plant Leaves - drug effects; Plant Leaves - genetics; Plant Leaves - metabolism; Plant nutrition; Plant Proteins - genetics; Plant Proteins - metabolism; Plant roots; Plant shading; Plants; RNA, Messenger - genetics; RNA, Messenger - metabolism; Senescence; Shading; Solubility - drug effects
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2012.04165.x

Retranslocation of iron (Fe) from source leaves to sinks requires soluble Fe binding forms. As much of the Fe is protein-bound and associated with the leaf nitrogen (N) status, we investigated the role of N in Fe mobilization and retranslocation under N deficiency-vs dark-induced leaf senescence.
By excluding Fe retranslocation from the apoplastic root pool, Fe concentrations in source and sink leaves from hydroponically grown barley (Hordeum vulgare) plants were determined in parallel with the concentrations of potential Fe chelators and the expression of genes involved in phytosiderophore biosynthesis.
N supply showed opposing effects on Fe pools in source leaves, inhibiting Fe export out of source leaves under N sufficiency but stimulating Fe export from source leaves under N deficiency, which partially alleviated Fe deficiency-induced chlorosis. Both triggers of leaf senescence, shading and N deficiency, enhanced NICOTIANAMINE SYNTHASE2 gene expression, soluble Fe pools in source leaves, and phytosiderophore and citrate rather than nicotianamine concentrations.
These results indicate that Fe mobilization within senescing leaves is independent of a concomitant N sink in young leaves and that phytosiderophores enhance Fe solubility in senescing source leaves, favoring subsequent Fe retranslocation.