Plasma membrane H+-ATPase in sorghum roots as affected by potassium deficiency and nitrogen sources

Abstract

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.

Keywords

• ammonium
• immunodetection
• k+ uptake
• nitrate
• sorghum bicolor
• vanadate