Effects of calmodulin inhibitors in plants. I. Synergism with fusicoccin in the stimulation of growth and H + secretion and in the hyperpolarization of the transmembrane electric potential

Abstract

The effects of some calmodulin-Ca 2+ complex inhibitors (trifluoperazine (TFP), chlorpromazine (CP) and the cis and trans isomers of flupenthixol) on both basal and fusicoccin(FC)-stimulated growth, proton extrusion and transmembrane electrical potential (PD) in different plant materials have been investigated. TFP and CP significantly promoted growth and acid secretion in the materials investigated. The stimulation of acid secretion under basal conditions was small (pea stems and maize coleoptiles) or not significant (maize roots), while it became important when the inhibitors were fed together with FC at suboptimal concentration (namely, concentrations inducing 20–30% of the maximum activation of electrogenic proton extrusion). A similar behaviour was induced by either of the two cis and trans flupenthixol isomers, which resulted equally active. The effect of the calmodulin inhibitors and that of FC at suboptimal concentrations appeared synergistic. The promoting effect of TFP on H + secretion in maize roots was associated with a marked hyperpolarization of the PD. These results provide a first indication that calmodulin might be in some way involved in the regulation of proton secretion and electrogenesis in higher plants.