Control of sodium transport in durum wheat

In many species, salt sensitivity is associated with the accumulation of sodium (Na(+)) in photosynthetic tissues. Na(+) uptake to leaves involves a series of transport steps and so far very few candidate genes have been implicated in the control of these processes. In this study, Na(+) transport was compared in two varieties of durum wheat (Triticum turgidum) L. subsp. durum known to differ in salt tolerance and Na(+) accumulation; the relatively salt tolerant landrace line 149 and the salt sensitive cultivar Tamaroi. Genetic studies indicated that these genotypes differed at two major loci controlling leaf blade Na(+) accumulation (R. Munns, G.J. Rebetzke, S. Husain, R.A. James, R.A. Hare [2003] Aust J Agric Res 54: 627-635). The physiological traits determined by these genetic differences were investigated using measurements of unidirectional (22)Na(+) transport and net Na(+) accumulation. The major differences in Na(+) transport between the genotypes were (1) the rate of transfer from the root to the shoot (xylem loading), which was much lower in the salt tolerant genotype, and (2) the capacity of the leaf sheath to extract and sequester Na(+) as it entered the leaf. The genotypes did not differ significantly in unidirectional root uptake of Na(+) and there was no evidence for recirculation of Na(+) from shoots to roots. It is likely that xylem loading and leaf sheath sequestration are separate genetic traits that interact to control leaf blade Na(+).