Plasma membrane H⁺-ATPase in sorghum roots as affected by potassium deficiency and nitrogen sources
Alvarez-Pizarro, J. C. | Gomes-Filho, E. | Prisco, J. T. | Grossi-De-Sá, M. F. | De Oliveira-Neto, O. B. | Da Rocha Fragoso, R.
We studied the influence of inorganic nitrogen sources (NO₃ ⁻ or NH₄ ⁺) and potassium deficiency on expression and activity of plasma membrane (PM) H⁺-ATPase in sorghum roots. After 15 d of cultivation at 0.2 mM K⁺, the plants were transferred to solutions lacking K⁺ for 2 d. Then, K⁺ depletion assays were performed in the presence or absence of vanadate. Further, PMs from K⁺-starved roots were extracted and used for the kinetic characterization of ATP hydrolytic activity and the immunodetection of PM H⁺-ATPase. Two major genes coding PM H⁺-ATPase (SBA1 and SBA2) were analyzed by real-time PCR. PM H⁺-ATPase exhibited a higher Vₘₐₓ and Kₘ in NH₄ ⁺-fed roots compared with NO₃ ⁻ -fed roots. The optimum pH of the enzyme was slightly lower in NO₃ ⁻ -fed roots than in NH₄ ⁺-fed roots. The vanadate sensitivity was similar. The expressions of SBA1 and SBA2 increased in roots grown under NH₄ ⁺. Concomitantly, an increased content of the enzyme in PM was observed. The initial rate of K⁺ uptake did not differ between plants grown with NO₃ ⁻ or NH₄ ⁺, but it was significantly reduced by vanadate in NH₄ ⁺-grown plants.
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