Adaptive strategy of Nitraria sibirica to transient salt, alkali and osmotic stresses via the alteration of Na⁺/K⁺ fluxes around root tips

Abstract

Nitraria sibirica Pall. is an important shrub with a strong salt-alkali tolerance, but the mechanism underlying this tolerance remains obscure. In this study, N. sibirica, with salt-sensitive Vigna radiata (Linn.) Wilczek as the control, was subjected to transient salt stress (100 mM NaCl), alkali stress (50 mM Na₂CO₃), and osmotic stress (175 mM mannitol). The ionic fluxes of Na⁺ and K⁺ in the root apical region were measured. Results show that, under salt and alkali stress, N. sibirica roots exhibited higher capacities to limit Na⁺ influx and reduce K⁺ efflux, thereby resulting in lower Na⁺/K⁺ ratios compared with V. radiata roots. Alkali stress induced stronger Na⁺ influx and K⁺ efflux in the root salt stress treatment; Na⁺ influx was mainly observed in the root cap, while K⁺ efflux was mainly observed in the elongation zone. While under osmotic stress, N. sibirica roots showed stronger Na⁺ efflux and weaker K⁺ efflux than V. radiata roots. Na⁺ efflux was mainly observed in the root elongation zone, while K⁺ efflux was in the root cap. These results reveal the ionic strategy of N. sibirica in response to transient salt, alkali, and osmotic stresses through the regulation of Na⁺/K⁺ flux homeostasis.

Keywords

Nirtaria sibirica / Na⁺/K⁺ fluxes / Na⁺/K⁺ ratios / Salt stress / Alkali stress / Osmotic stress