The 14-3-3 proteins are a family of proteins present in a number of isoforms in all eukaryotes and involved in the control of many cellular functions. Regulation of different activities is achieved by binding to phosphorylated targets through a conserved mechanism. Although in many systems isoform specificity has been demonstrated, the underlying molecular basis is still unclear. The sequences of 14-3-3 isoforms are highly conserved, divergence occurring at the N- and C-terminal regions. Recently it has been suggested that the C-terminal domain of 14-3-3 may regulate protein binding to the targets. Here we study the role of the C-terminal region of maize isoform GF14-6 in the interaction with the plant plasma membrane H(+)-ATPase. Results obtained demonstrate that removal of the last 22 amino acids residues of GF14-6 increases binding to H(+)-ATPase and stimulation of its activity. C-terminal deletion, moreover, reduces 14-3-3 sensitivity to cations. We also show that a peptide reproducing the GF14-6 C-terminus is able to bind to the C-terminal domain of H(+)-ATPase and to stimulate the enzyme activity. The implications of these findings for a integrated model of 14-3-3 interaction with H(+)-ATPase are discussed.