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Growth and proline content in NaCl stressed plants of annual medic species

Wild populations of Medicago ciliaris and Medicago polymorpha were subjected to four salt treatments 0, 50, 100 and 150 mM NaCl, plant growth and proline concentration in leaves were assessed. The analyzed data revealed significant variability in salt response within and between the two species, depending on the salinity level. It was found that high NaCl concentrations affected all the growth parameters. However, the reduction was more important at higher NaCl concentrations and the highest reduction was obtained for the populations of Medicago polymorpha where it reached around 90% in root length at 150 mM NaCl for Pmar. The Tunisian population of Medicago ciliaris, prospected on soils affected by salinity, was the best tolerant in all ecotypes studied in this work. This population, exhibits a particular adaptability to salt environment at both germination and seedling stage. Furthermore, the correlation among the studied plants sensitivity and leaf proline concentration showed that high proline contents were related to their reactivity to salt. Consequently, it appeared that proline biosynthesis occurred presumably as a consequence of disturbance in cell homoeostasis and reflected poor performance and greater damage in response to salt stress. These findings indicated that this osmolytes content may be used as another useful criterion to differentiate salt-tolerant from salt sensitive plant in annual medics.