Istological investigation on in vitro salinity response in Limonium cordatum (L.) Mill., a Mediterranean endemism

L. cordatum is an alophylous plant, it prefers rocky habitat and it needs a calcareous substrate; the species lives in Italy in a very restricted area (Liguria Region – CÔte d’Azur), close to the Mediterranean sea, where the human pressure due to tourism and industrial activities is really heavy and undermines its survival; for this reason it is included in the regional Red Lists of threatened plants in the Liguria Region (I) and in the Dept. des Alpes Maritimes (F) (I.U.C.N., 1998). For this plant a protocol of in vitro propagation was established by Savona et al. in 2008 with the aim to achieve a successful conservation strategy. Furthermore the species was taken into consideration as model plant to study the response mechanism to salinity stress. Test media were prepared with the agarized MS growth medium (1962) with or without BA 0.2 mg l-1 and adding several NaCl concentrations (0, 150, 300, 450, 600 mmol l-1); shoots were cultured at low light intensity (PPFD: 14 μE m-2 s-1), 16 h photoperiod and at 23°C ± 1. The hystological analysis was performed at different growth conditions, in order to study the anatomy of the plant and the morphological reorganisation of leaf tissues. Salt glands were described in vitro in this species for the first time in all the Plumbaginaceae family; root primordia were present but inhibited in their development at the highest salt concentration. An evident decrease of viability and, in consequence, of all the growth parameters occurred, in fact, over 450 mmol l-1 already after 30 days of culture.