Seed germination, antioxidant enzymes activity and proline content in medicinal plant Tagetes minuta under salinity stress

In the present study, the effect of salinity on seed germination, free proline, soluble proteins, and sugar contents, as well as antioxidant enzymes activity of Tagetes minuta seedlings were determined. The seeds were treated with five concentrations of NaCl and KNO3 (0, 50, 100, 200, 300 and 500 mM) at 25/15 degrees C temperature under 12-h light/12-h dark photoperiods. According to the results, the germination percentage decreased with increasing salinity rate. The lowest percentage of germination was obtained at 200 mM of NaCl and KNO3. The germination of T. minuta seeds at concentrations above 200 mM of both salts stopped. In all concentrations of NaCl, seed germination percentage was higher in comparison with KNO3. The proline, soluble protein and sugar contents as well as superoxide dismutase, peroxidase, and catalase activities increased with increasing of salinity levels. However, the changes in studied characteristics in NaCl treated seedling was higher than KNO3 treatments. The results suggested that the T. minuta seedlings were able to tolerate salinity up to 200 mM of NaCl or KNO3. This ability was attributed to an increase of antioxidant enzyme activities, proline and soluble sugar contents in crossing with salinity conditions. It has concluded that the accumulation of compatible organic solute might be a method employed by T. minuta to adapt to salinity stress.