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 Salicorniaherbacea L. grown either in light or dark. Its optimal concentrationwas around 0.1–0.2 M and its promoting effect was muchmore prominent in the dark. Gibberellic acid at 10^–5 Mstimulated hypocotyl elongation in light but not in the dark.Indole-3-acetic acid and kinetin were ineffective in promotinghypocotyl elongation. In light, gibberellic acid and NaCl synergisticallyenhanced 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 hypocotylincreased 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 extensibilityof the hypocotyl cell wall. Synergistic interaction in increasingthe extensibility was observed between gibberellic acid andNaCl. Stress-relaxation analysis of mechanical properties ofthe hypocotyl wall revealed that gibberellic acid and NaCl actedsynergistically in decreasing minimum relaxation time. Basedon these results, a possible mechanism by which gibberellicacid and NaCl regulate hypocotyl elongation of Salicornia herbaceaL., a typical halophilic plant, is discussed. ¹ Present address: Laboratory of Biology, Tezukayama College,Gakuen Minami, Nara 631, Japan. (Received June 13, 1978; )