Involvement of cation channels and NH<sub>4</sub><sup>+</sup>-sensitive K<sup>+</sup> transporters in Na<sup>+</sup> uptake by cowpea roots under salinity

Abstract

Na+ accumulation was investigated in the roots of 11-d-old cowpea [Vigna unguiculata (L.) Walp.] plants. The relative contribution of different membrane transporters on Na+ uptake was estimated by applying Ca2+, K+, NH4 +, and pharmacological inhibitors. Na+ accumulation into the root symplast was decreased by half in the presence of 1 mM Ca2+ and it was almost abolished by 100 mM K+. The inhibitory effect of external NH4+ on Na+ accumulation was more pronounced in the roots of NH4 +-free growing plants. Na+ accumulation was reduced about 73 % by 0.1 mM flufenamate and it was almost blocked by 2 mM quinine. In addition, 20 mM tetraethylammonium and 1.0 mM Cs+ decreased Na+ accumulation by 28 and 30 %, respectively. These results evidenced that low-affinity Na+ uptake by cowpea roots depends on Ca2+-sensitive and Ca2+-insensitive pathways. The Ca2+-sensitive pathway is probably mediated by nonselective cation channels and the Ca2+-insensitive one may involve K+ channels and to a lesser extent NH4 +-sensitive K+ transporters.