Alkali grass resists salt stress through high [K+] and an endodermis barrier to Na+

Abstract

In order to understand the salt‐tolerance mechanism of alkali grass (Puccinellia tenuiflora) compared with wheat (Triticum aestivum L.), [K⁺] and [Na⁺] in roots and shoots in response to salt treatments were examined with ion element analysis and X‐ray microanalysis. Both the rapid K⁺ and Na⁺ influx in response to different NaCl and KCl treatments, and the accumulation of K⁺ and Na⁺ as the plants acclimated to long‐term stress were studied in culture‐ solution experiments. A higher K⁺ uptake under normal and saline conditions was evident in alkali grass compared with that in wheat, and electrophysiological analyses indicated that the different uptake probably resulted from the higher K⁺/Na⁺ selectivity of the plasma membrane. When external [K⁺] was high, K⁺ uptake and transport from roots to shoots were inhibited by exogenous Cs⁺, while TEA (tetraethylammonium) only inhibited K⁺ transport from the root to the shoot. K⁺ uptake was not influenced by Cs⁺ when plants were K⁺ starved. It was shown by X‐ray microanalysis that high [K⁺] and low [Na⁺] existed in the endodermal cells of alkali grass roots, suggesting this to be the tissue where Cs⁺ inhibition occurs. These results suggest that the K⁺/Na⁺ selectivity of potassium channels and the existence of an apoplastic barrier, the Casparian bands of the endodermis, lead to the lateral gradient of K⁺ and Na⁺ across root tissue, resulting not only in high levels of [K⁺] in the shoot but also a large [Na⁺] gradient between the root and the shoot.