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

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RESUMO

The rapid growth responses of oat (var. Victory) coleoptile segments treated with millimolar concentrations of the chlorides of La3+, Ca2+, K+, and NH4+, respectively, have been measured. La3+ and Ca2+ initially depressed the endogenous elongation rate. In the case of La3+ 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 La3+. NH4+ produced an immediate rapid increase in elongation rate. La3+ did not behave as a “super calcium” in its action upon the spontaneous growth response. The prolonged elongation of the La3+-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.

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