Studies on the Mechanism of Salt Tolerance in Salicornia europaea L. : II. High osmosis of epidermal cells in stem

Abstract

To understand how cells sense and respond to salt stress, we investigate changes in plasmolitic concentration to NaCl of epidermal cells in Salicornia europaea during the growth period. The inorganic ion concentration in tissues and plasmolitic responses to NaCl of epidermal cells in wild Salicornia were compared with other halophytes. Cell responses to high salt concentration were compared with plants grown in MS medium as a low salinity. The incipient plasmolytic NaCl concentration in epidermal cells in Salicornia stems rose from 1.6% to 2.2% during the growth period. Main inorganic ions in Salicornia at the end of growth stage were 63 mM Na⁺ and 107 mM Cl^- per 100 g fresh weight. When plants were grown in MS medium, the size of epidermal cells was about 2 fold large, and osmotic pressure in plants was 35-50% low compared with wild plant cells. Incipient plasmolytic NaCl concentration in epidermal cells of plants grown in wild and MS medium was almost same. However, most of the epidermal cells grown in MS medium showed severe plasmolysis under hypertonic NaCl solutions. The results suggest that the cells of Salicornia can accumulate NaCl during the growth period and accumulated NaCl may make adjustment of osmotic pressure in the cells. By contrast with other halophytes, Salircornia showed high Na⁺ and Cl^- concentrations in tissues and high plasmolitic concentration to NaCl in epidermal cells.