Effect of K(+) and Cl (-) ion gradients upon apex regeneration in Acetabularia mediterranea.

Regeneration of a new apex and electrical activity by anucleate posterior stalk segments (PSS) of Acetabularia mediterranea under imposed transcellular concentration gradients of K(+) and Cl(-) has been studied. In a 3 vs. 30 mM K(+) and in a 26 vs. 545 mM Cl(-) gradient, respectively, the PSS preferably regenerate at that end exposed to the low K(+) (replaced by Na(+)) and low Cl(-) (replaced by SO 4 (2-) ), respectively. The effect of the K(+) gradient confirms previous work where voltage-clamped PSS regenerated at the electrically hyperpolarized end (Novák and Bentrup, Planta 108, 227, 1972). The stimulation of regeneration by low Cl(-), that is, at the depolarized end of the PSS, might be mediated by the electrical impulses arising at this end.