Requirement of sodium chloride for the action of gibberellic acid in stimulating hypocotyl elongation of a halophyte, Salicornia herbacea L.

NaCl stimulated hypocotyl elongation of the halophyte Salicornia herbacea L. grown either in light or dark. Its optimal concentration was around 0.1–0.2 M and its promoting effect was much more prominent in the dark. Gibberellic acid at 10−5 M stimulated hypocotyl elongation in light but not in the dark. Indole-3-acetic acid and kinetin were ineffective in promoting hypocotyl elongation. In light, gibberellic acid and NaCl synergistically enhanced hypocotyl elongation when both were given simultaneously. The action of NaCl could be replaced by KCl, but not by mannitol. Osmotic pressure of the epidermis of the Salicornia hypocotyl increased in response to gibberellic acid and/or NaCl treatment. Na+ content in the hypocotyl increased with NaCl application. Gibberellic acid and NaCl when given alone increased the extensibility of the hypocotyl cell wall. Synergistic interaction in increasing the extensibility was observed between gibberellic acid and NaCl. Stress-relaxation analysis of mechanical properties of the hypocotyl wall revealed that gibberellic acid and NaCl acted synergistically in decreasing minimum relaxation time. Based on these results, a possible mechanism by which gibberellic acid and NaCl regulate hypocotyl elongation of Salicornia herbacea L., a typical halophilic plant, is discussed.