Figure 8.

Competition between Fusicoccin (FC) and tenuazonic acid (TeA). (a) Activation of Spinacia oleracea plasma membrane (PM) H⁺‐ATPase preincubated with either FC, 14‐3‐3 or FC/14‐3‐3 before assay start. (b) Dose‐dependent TeA inhibition of S. oleracea PM H⁺‐ATPase preincubated with FC and 14‐3‐3 protein before assay start. (c) Dose‐dependent FC/14‐3‐3 activation of S. oleracea PM H⁺‐ATPase preincubated with 20 μM TeA before assay start. (b, c) Data were analyzed using nonlinear regression and fitted to log[agonist] (μM) vs the normalized response (variable slope) to determine the half maximal effective concentration (EC₅₀) value. FC (10 µM) and 14‐3‐3 (1 µg) were used in all treatments. Treatments with 14‐3‐3 alone or FC/14‐3‐3 were significantly different from nontreated (**, P < 0.01; ***, P < 0.001). Experiments were performed in triplicates of two independent PM fractions, and values represent means ± SEM (n = 6).