Rapid Growth Responses of Avena Coleoptile Segments to Lanthanum and Other Cations

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.