Involvement of cation channels and NH₄+-sensitive K+ transporters in Na+ uptake by cowpea roots under salinity

摘要

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. Additional key words Ca2+-sensitive and Ca2+-insensitive pathways - K+ channels - Na+ accumulation - nonselective cation channels - salt stress - Vigna unguiculata Acknowledgements: We thank to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP) for financial support. J.A.G.S. is honoured researcher of CNPq and E.L.V, R.F.C., J.M.M. and S.L.F.S. were CNPq fellowship granted students.