Rapid Growth Responses of <i>Avena</i> Coleoptile Segments to Lanthanum and Other Cations

Abstract

The rapid growth responses of oat (var. Victory) coleoptile segments treated with millimolar concentrations of the chlorides of La(3+), Ca(2+), K(+), and NH(4) (+), respectively, have been measured. La(3+) and Ca(2+) initially depressed the endogenous elongation rate. In the case of La(3+) a prolonged stimulatory effect on the rate of elongation was produced by concentrations of 50 millimolar down to 20 micromolar after an initial depression of elongation rate. The effect of K(+) was slightly stimulatory and showed a synergistic effect in combination with La(3+). NH(4) (+) produced an immediate rapid increase in elongation rate. La(3+) did not behave as a "super calcium" in its action upon the spontaneous growth response. The prolonged elongation of the La(3+)-treated segments exhibiting the spontaneous growth response is apparently a newly observed effect. These rapid growth responses are interpreted as an interaction between anionic lipid-protein complexes in the plasmalemma and the respective ions.