Sodium hyperaccumulators in the Caryophyllales are characterized by both abnormally large shoot sodium concentrations and [Na]shoot/[Na]root quotients greater than unity

Background and Aims Some Caryophyllales species accumulate abnormally large shoot sodium (Na) concentrations in non-saline environments. It is not known whether this is a consequence of altered Na partitioning between roots and shoots. This paper tests the hypotheses (1) that Na concentrations in shoots ([Na](shoot)) and in roots ([Na](root)) are positively correlated among Caryophyllales, and (2) that shoot Na hyperaccumulation is correlated with [Na](shoot)/[Na](root) quotients. Methods Fifty two genotypes, representing 45 Caryophyllales species and 4 species from other angiosperm orders, were grown hydroponically in a non-saline, complete nutrient solution. Concentrations of Na in shoots and in roots were determined using inductively coupled plasma mass spectrometry (ICP-MS). Key Results Sodium concentrations in shoots and roots were not correlated among Caryophyllales species with normal [Na](shoot), but were positively correlated among Caryophyllales species with abnormally large [Na](shoot). In addition, Caryophyllales species with abnormally large [Na]shoot had greater [Na](shoot)/[Na](root) than Caryophyllales species with normal [Na](shoot). Conclusions Sodium hyperaccumulators in the Caryophyllales are characterized by abnormally large [Na](shoot), a positive correlation between [Na](shoot) and [Na](root), and [Na](shoot)/[Na](root) quotients greater than unity.

Automated summary

In Caryophyllales species, there is no correlation between shoot and root sodium concentrations in species with normal shoot sodium levels, but a positive correlation in species with abnormally high shoot sodium levels. Additionally, species with abnormally high shoot sodium levels have higher shoot/root sodium concentration ratios than species with normal shoot sodium levels.