Monovalent Cations and Growth Regulation. I. Growth Responses in Cucumber Hypocotyl Segments

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Abstract
The elongation of etiolated cucumber hypocotyl segments was stimulated by KC1 and a number of other K salts at a concentration of 0.02 N K+ The effect of KC1 was not evident until 14 hours after the beginning of treatment. NaCl, LiCl, and RbCl enhanced elongation of the segments, and their dosage-response curves were similar to that for KC1. At supraoptimal concentrations, LiCl inhibited segment growth. CsCl was inhibitory at all concentrations tested. NH4CI also promoted elongation, but not as effectively as did the alkali cations. CaC2, C0CI2, MgCl2 and NiCl2 did not enhance growth when tested at the same concentrations as the monovalent cations. C0CI2 promoted strongly at 10-3 [image], and NiCl2 was slightly active at 10-4 [image]M. It is suggested that the nutritional requirement for K results from a specific involvement in certain enzyme systems and from a relatively nonspecific role related to the elongation response described here.