Phosphorus Levels Influence Plasma Membrane H+-ATPase Activity and K+, Ca2+, and Mg2+ Assimilation in Green Bean

Few studies have evaluated the changes in nutrient uptake in response to the availability of other nutrients, particularly cations [potassium (K), magnesium (Mg), and calcium (Ca)]. Therefore, the objective of the present work was to determine the effects of deficient, adequate, or excessive levels of phosphorus (P) on plasma membrane H+-ATPase activity and K+, Ca2+, and Mg2+ assimilation in green bean plants (Phaseolus vulgaris L. cv. Strike). A growth chamber study was conducted with different P levels applied to the nutrient solution: P-1, 0.5 mM; P-2, 1 mM; P-3, 2 mM; P-4, 4 mM; P-5, 6 mM; and P-6, 8 mM. Forms of cations analyzed were total and soluble K+, Ca2+, and Mg2+ and plasma membrane H+-ATPase (EC 3.6.1.35) activity, basal or induced with K+ (K+-ATPase), Ca2+ (Ca2+-ATPase), and Mg2+ (Mg2+-ATPase). Phosphorus treatments caused a significant and progressive increase in total and soluble K+, Ca2+, and Mg2+, with P-6 registering the greatest concentration and P-1 the lowest. Also, P doses significantly affected plasma membrane H+-ATPase activity, both basal ATPase and that induced with K+, Ca2+, and Mg2+. Therefore, P was the key factor enhancing plasma membrane H+-ATPase activity and improving K+, Ca2+, and Mg2+ uptake. Cations always were present in the nutritive solution; however, only increasing P concentration increased the cation uptake. The knowledge about the change in nutrient input in response to the availability of other nutrients could lead to the development of better management practices to minimize fertilizer input. Our results show that P is an important element for plasma membrane H+-ATPase activity and K+, Ca2+, and Mg2+ uptake.