James Richard A, Davenport Romola J, Munns Rana
CSIRO Plant Industry, Canberra, Australian Capital Territory 2601, Australia.
Plant Physiol. 2006 Dec;142(4):1537-47. doi: 10.1104/pp.106.086538. Epub 2006 Oct 6.
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).
硬粒小麦（Triticum turgidum L. subsp. durum Desf.）品系149含有两个新的主要基因，可将Na(+)排除在叶片之外，分别命名为Nax1和Nax2。这些基因被分离成单基因家族，并选择了近等基因纯合系。含有Nax1或Nax2的品系从根到地上部的Na(+)转运速率低于其近等基因配对品系，这是由于木质部的净装载速率较低，而不是由于从土壤中的净吸收速率较低或韧皮部中再转运速率较高。Nax1和Nax2品系从根到地上部的K(+)转运速率也较高，从而增强了对K(+)相对于Na(+)的选择性。含有Nax1的品系与含有Nax2的品系不同，当Na(+)进入地上部时，它会从木质部卸载Na(+)，从而使Na(+)保留在叶基部，导致叶鞘与叶片的Na(+)浓度比很高。沿叶片的Na(+)组织浓度梯度表明，Na(+)不断从木质部中被去除。Nax2品系不会在叶基部保留Na(+)，这表明它仅在根中起作用。因此，Nax2基因与面包小麦（Triticum aestivum）中的Kna1具有相似的功能。
