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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Physiological Characterization of Two Genes for Na⁺ Exclusion in Durum Wheat, Nax1 and Nax2¹

CSIRO Plant Industry, Canberra, Australian Capital Territory 2601, Australia (R.A.J., R.M.); and Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, United Kingdom (R.J.D.)

Durum wheat (Triticum turgidum L. subsp. durum Desf.) Line 149 contains two novel major genes for excluding Na⁺ from leaf blades, named Nax1 and Nax2. The genes were separated into families containing a single gene and near-isogenic homozygous lines were selected. Lines containing either Nax1 or Nax2 had lower rates of Na⁺ transport from roots to shoots than their near-isogenic pairs due to lower rates of net loading of the xylem, not to lower rates of net uptake from the soil or higher rates of retranslocation in the phloem. Nax1 and Nax2 lines also had higher rates of K⁺ transport from root to shoot, resulting in an enhanced discrimination of K⁺ over Na⁺. Lines containing Nax1 differed from those containing Nax2 by unloading Na⁺ from the xylem as it entered the shoot so that Na⁺ was retained in the base of the leaf, leading to a high sheath to blade ratio of Na⁺ concentration. Gradients in tissue concentrations of Na⁺ along the leaf suggested that Na⁺ was continually removed from the xylem. The Nax2 line did not retain Na⁺ in the base of the leaf, suggesting that it functioned only in the root. The Nax2 gene therefore has a similar function to Kna1 in bread wheat (Triticum aestivum).

² Present address: Oxford Institute of Ageing, Manor Rd. Building, Manor Rd., Oxford OX1 3UQ, UK.

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: Richard A. James (richard.james{at}csiro.au).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.086538

^* Corresponding author; e-mail richard.james{at}csiro.au; fax 61–2–6246–5399.

Received July 12, 2006; accepted August 23, 2006; published October 6, 2006.

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