Puccinellia tenuiflora Exhibits Stronger Selectivity for K⁺ over Na⁺ than Wheat

Abstract

The characteristics of selectivity for K⁺ over Na⁺ by the roots of the halophyte Puccinellia tenuiflora were investigated in comparison with the glycophyte wheat (Triticum aestivum). Under various NaCl concentrations, the concentrations of K⁺ in the shoots of P. tenuiflora were 16–24% lower than those of wheat, whereas the concentrations of K⁺ in Puccinellia roots were 2.8–4.0 times higher than those of wheat. In 200 mM NaCl, the concentrations of Na⁺ in shoots of P. tenuiflora and wheat were similar under high K⁺ levels, but the concentrations of Na⁺ in wheat were 1.6 times higher than those in Puccinellia under low K⁺ levels. The concentrations of K⁺ in roots of P. tenuiflora were 1.5–2.0 times higher than those of wheat under low K⁺ levels. Formulas are given for calculating net selective absorption (SA) capacity and selective transport (ST) capacity by roots for K⁺ over Na⁺. We interpret SA as the net capacity of selectively absorbing K⁺ over Na⁺ by epidermal and cortical cells of whole plant roots into the root symplast. ST could reflect the net capacity of selection for K⁺ over Na⁺ transport from whole root stelar symplast to the xylem vessels. The lower ST value of P. tenuiflora might be the reason for accumulation of K⁺ in its roots. The SA values of P. tenuiflora and wheat were approximately equivalent in the low-affinity K⁺ uptake range. The SA values of the former were about two times higher than that of the latter in the high-affinity K⁺ uptake range, showing the root high-affinity K⁺ uptake system of the halophyte P. tenuiflora has a stronger capacity for K⁺ uptake.

Keywords:

• Halophyte
• Ion selectivity
• NaCl stress
• Potassium
• Puccinellia tenuiflora
• Sodium
• Triticum aestivum
• Uptake

Acknowledgments

We are very grateful and indebted to Professor T.J. Flowers from University of Sussex of UK and A. McNeill from Adelaide University of Australia for critically reviewing the manuscript and for the valuable suggestions. This work was supported by the National Natural Science Foundation of China (30270947), the National Key Basic Pre-research Special Funds and Key Basic Research Special Funds of MOST of China (2002CCC01600, G1999011705). S.M. Wang is grateful to the Royal Society of the U.K. for a Royal Society Sino-British Fellowship Trust Award.