Seed germination, growth, and osmotic adjustment in response to NaCl in a rare succulent halophyte from southeastern Spain

Abstract

In this paper, some issues of the autoecology of Halocnemum strobilaceum (a rare succulent halophyte that occurs in southeastern Spain) are examined, particularly the germination process and the first stages of plant development. In regards to germination, this species shows the general pattern of halophytes under increased salt stress (reduced germination and germination rate). What stands out is the extreme salt tolerance of H. strobilaceum seeds. The stimulation of root length by the presence of salt probably plays an important role in avoiding salt stress at surface-level soils, within salt concentrations where germination still occurs. Halocnemum strobilaceum typically accumulates Na⁺ ions, which, combined with Cl⁻, contributes to the internal osmotic potential. The accumulation of both ions clearly increases with an increase in salinity stress. In contrast, accumulation of K⁺, Mg²⁺, and Ca²⁺ decreases with an increase in salinity stress. Glycinebetaine contents are approximately 100 times greater than proline contents, although their contribution was significant only if cell compartmentalization was considered. The accumulation of ions along with the osmoprotective compounds glycinebetaine and proline allows seedlings to mantain a lower internal osmotic potential than that of the growth medium, which is necessary for water uptake in saline soils.