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Sodium/potassium selectivity and pleiotropy in stl2, a highly salt-tolerant mutation of Ceratopteris richardii

Warne, T.R., Hickok, L.G., Sams, C.E., Vogelien, D.L.
Plant, cell and environment 1999 v.22 no.8 pp. 1027-1034
rubidium, salt tolerance, Ceratopteris, magnesium chloride, ion transport, cations, magnesium, cytosol, potassium, sodium, mutants, sodium chloride, genetic variation, genotype
The roles of Na+ and K+ (Rb+) uptake were further studied in a NaCl-tolerant strain of Ceratopteris richardii containing the stl2 mutation by direct comparison with the wild-type strain. In addition to Na+ tolerance, stl2 also confers tolerance to Mg2+ and sensitivity to K+. In addition to higher K+ (Rb+) uptake at concentrations commonly associated with low-affinity K+ transport, stl2 maintained higher uptake down to 0.1 mol m(-3) Rb+. Up to a 25-fold excess of Na+ had little effect in either genotype on K+ (Rb+) uptake at low concentrations, i.e. 0.2 and 0.5 mol m(-3) RbCl. Pretreatment with K+ (20 mol m(-3)) inhibited uptake of K+ (Rb+) in the wild type, whereas concurrent inclusion of K+ inhibited uptake of Rb+ more in stl2. In the absence of K+, Na+ uptake (0.01-60 mol m(-3)) was nearly identical in the wild type and stl2. K+ inhibited Na+ uptake more effectively in stl2 than the wild type, especially at 60 mol m(-3) Na+. Greater inhibition of K+ uptake in stl2 occurred with MgCl2 or TEA (tetraethylammonium chloride) preincubation or with simultaneous inclusion of Al(3+) (Al2SO4). The higher effective velocity of K+ uptake at a wide range of concentrations and the enhanced selectivity for K+ and against Na+ contribute to the preservation of higher cytosolic K+ and lower Na+ under salinity stress.