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

• Published in: Journal of plant physiology 2011-09, Vol.168 (14), p.1617-1626
• Main Authors: Alvarez-Pizarro, Juan Carlos, Gomes-Filho, Enéas, Prisco, José Tarquínio, Grossi-de-Sá, Maria Fátima, de Oliveira-Neto, Osmundo Brilhante
• Format: Article
• Language: English
• Subjects: Biological Transport; Cell Membrane - enzymology; Cell Membrane - metabolism; Hydrogen-Ion Concentration; Hydrolysis; Kinetics; Nitrogen - metabolism; Plant Roots - enzymology; Plant Roots - metabolism; Potassium - analysis; Potassium - metabolism; Protein Isoforms; Proton-Translocating ATPases - metabolism; Quaternary Ammonium Compounds - pharmacology; Solutions; Sorghum - enzymology; Sorghum - metabolism
• ISSN: 1618-1328
• DOI: 10.1016/j.jplph.2011.03.002

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.