Responses to salt stress in Juncus acutus and J. maritimus during seed germination and vegetative plant growth

Abstract

Responses to increasing salinity, during seed germination and vegetative plant growth, were studied in two related species of Juncus, J. maritimus and J. acutus. In both species, germination was optimal in the absence of salt, reduced by about 50% in the presence of 200 mM NaCl, and completely inhibited by NaCl concentrations above 300 mM. Previous exposure of the seeds to salt, up to 500 mM NaCl, did not affect the germination capacity in J. acutus, and clearly enhanced it in J. maritimus. A concentration-dependent inhibition of plant growth was observed in the presence of NaCl for both species, together with the parallel accumulation of sodium ions in the leaves, as determined by cation exchange HPLC. Regarding the levels of divalent cations, in J. acutus Ca²⁺ and Mg²⁺ increased up to about two-fold in plants treated with 500 mM NaCl, as compared to control plants, whereas in J. maritimus they were three- to four-fold higher than in J. acutus in the absence of salt, and did not change significantly with increasing NaCl concentrations. These results suggest that Ca²⁺ and Mg²⁺ participate in defence mechanisms against salt stress, which would be constitutive in J. maritimus and salt-inducible in J.acutus.

Keywords:

• Abiotic stress
• cation accumulation
• ion exchange HPLC
• Juncus
• salt tolerance
• seed germination

Acknowledgements

We thank Mr. Francisco Collado, from the “Oficina Técnica de La Albufera”, El Saler (Valencia), for his help with the fieldwork in the Natural Park of Albufera, and to Dr. Lynne Yenush, from the Instituto de Biología Molecular y Celular de Plantas, for her revision of the English grammar and style of the text.