title: NH(4)(+)-stimulated low-K(+) uptake is associated with the induction of H(+) extrusion by the plasma membrane H(+)-ATPase in sorghum roots under K(+) deficiency.
abstract: The effect of external inorganic nitrogen and K(+) content on K(+) uptake from low-K(+) solutions and plasma membrane (PM) H(+)-ATPase activity of sorghum roots was studied. Plants were grown for 15 days in full-nutrient solutions containing 0.2 or 1.4mM K(+) and inorganic nitrogen as NO(3)(-), NO(3)(-)/NH(4)(+) or NH(4)(+) and then starved of K(+) for 24, 48 and 72 h. NH(4)(+) in full nutrient solution significantly affected the uptake efficiency and accumulation of K(+), and this effect was less pronounced at the high K(+) concentration. In contrast, the translocation rate of K(+) to the shoot was not altered. Depletion assays showed that plants grown with NH(4)(+) more efficiently depleted the external K(+) and reached higher initial rates of low-K(+) uptake than plants grown with NO(3)(-). One possible influence of K(+) content of shoot, but not of roots, on K(+) uptake was evidenced. Enhanced K(+)-uptake capacity was correlated with the induction of H(+) extrusion by PM H(+)-ATPase. In plants grown in high K(+) solutions, the increase in the active H(+) gradient was associated with an increase of the PM H(+)-ATPase protein concentration. In contrast, in plants grown in solutions containing 0.2mM K(+), only the initial rate of H(+)-pumping and ATP hydrolysis were affected. Under these conditions, two specific isoforms of PM H(+)-ATPase were detected, independent of the nitrogen source and deficiency period. No change in enzyme activity was observed in NO(3)(-)-grown plants. The results suggest that K(+) homeostasis in NH(4)(+)-grown sorghum plants may be regulated by a high capacity for K(+) uptake, which is dependent upon the H(+)-pumping activity of PM H(+)-ATPase.
authors: Departamento de Bioquímica e Biologia Molecular and Instituto Nacional de Ciência e Tecnologia em Salinidade (INCTSal/CNPq), Universidade Federal do Ceará, Caixa Postal 6039, 60455-900 Fortaleza, Ceará, Brazil.
authors: Juan Carlos
authors: JC
authors: Alvarez-Pizarro
authors: Enéas
authors: E
authors: Gomes-Filho
authors: José Tarquínio
authors: JT
authors: Prisco
authors: Maria Fátima
authors: MF
authors: Grossi-de-Sá
authors: Osmundo Brilhante
authors: OB
authors: de Oliveira-Neto
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D009584:Nitrogen / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000378:metabolism; D011188:Potassium / Q000032:analysis / Q000378:metabolism*; D020033:Protein Isoforms; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D012996:Solutions; D045868:Sorghum / Q000201:enzymology / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D006180:Proton-Translocating ATPases; D009584:Nitrogen; D011188:Potassium