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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

The Analysis of Arabidopsis Nicotianamine Synthase Mutants Reveals Functions for Nicotianamine in Seed Iron Loading and Iron Deficiency Responses^{1,[C],[W],[OA]}

Department of Biosciences–Botany, Saarland University, D–66123 Saarbrücken, Germany (M.K., M.S., P.B.); Department of Molecular Biology of Plants, Heidelberg Institute of Plant Sciences, D–69120 Heidelberg, Germany (M.W., R.H.); and Leibniz Institute for New Materials GmbH, D–66123 Saarbrücken, Germany (C.F.-S.)

Nicotianamine chelates and transports micronutrient metal ions in plants. It has been speculated that nicotianamine is involved in seed loading with micronutrients. A tomato (Solanum lycopersicum) mutant (chloronerva) and a tobacco (Nicotiana tabacum) transgenic line have been utilized to analyze the effects of nicotianamine loss. These mutants showed early leaf chlorosis and had sterile flowers. Arabidopsis (Arabidopsis thaliana) has four NICOTIANAMINE SYNTHASE (NAS) genes. We constructed two quadruple nas mutants: one had full loss of NAS function, was sterile, and showed a chloronerva-like phenotype (nas4x-2); another mutant, with intermediate phenotype (nas4x-1), developed chlorotic leaves, which became severe upon transition from the vegetative to the reproductive phase and upon iron (Fe) deficiency. Residual nicotianamine levels were sufficient to sustain the life cycle. Therefore, the nas4x-1 mutant enabled us to study late nicotianamine functions. This mutant had no detectable nicotianamine in rosette leaves of the reproductive stage but low nicotianamine levels in vegetative rosette leaves and seeds. Fe accumulated in the rosette leaves, while less Fe was present in flowers and seeds. Leaves, roots, and flowers showed symptoms of Fe deficiency, whereas leaves also showed signs of sufficient Fe supply, as revealed by molecular-physiological analysis. The mutant was not able to fully mobilize Fe to sustain Fe supply of flowers and seeds in the normal way. Thus, nicotianamine is needed for correct supply of seeds with Fe. These results are fundamental for plant manipulation approaches to modify Fe homeostasis regulation through alterations of NAS genes.

² These authors contributed equally to the article.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Petra Bauer (p.bauer{at}mx.uni-saarland.de).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.136374

^* Corresponding author; e-mail p.bauer{at}mx.uni-saarland.de.

Received January 30, 2009; accepted March 16, 2009; published March 20, 2009.