Influence of nitrogen fertilization on K+, Mg2+ and Ca2+ concentrations and on its bioindicators in roots and leaves of green bean plants

Abstract

The pyruvate kinase (PK) and ATPase activities taking part in nitrogen (N) assimilation is essential for the growth and development of plants. Studies on the kinetics of these enzymes reveal that its activities are dependent of the cofactors K⁺, Ca²⁺, and Mg²⁺. Therefore, the objective of the present work was to determine the effect of different doses of N on enzymatic activities of ATPase and PK as potentials biochemical indicators of the levels of K⁺, Mg²⁺, and Ca²⁺ in the roots and leaves of green bean plants. The N was applied to the nutrient solution as NH₄NO₃ at the following rates: 1.5, 3.0, 6.0, 12.0, 18.0, and 24.0 mM of N. These results indicate that deficient conditions of N (N1 and N2) were characterized by the lowest accumulation of K⁺, Mg²⁺ and Ca²⁺ in both total and soluble forms, and also minimum activities of PK and ATPase induced by K⁺, Mg²⁺ and Ca²⁺, with respect to the activity of basal PK and ATPase; this could mean near optimum conditions for these cations. On the contrary, high-N treatments (N4, N5 and N6) were characterized by presenting decreasing concentrations of total and soluble K⁺, Mg²⁺ and Ca²⁺ in roots and leaves of green bean plants; however, the activities of PK and ATPase induced with K⁺, Mg²⁺ and Ca²⁺ were increased reaching their maximum activity with respect to basal PK and ATPase, both enzymes reflecting the level of cations in roots and leaves, hence being considered as good physiological bioindicators of these cations.