Methyl jasmonate improves salinity resistance in German chamomile (Matricaria chamomilla L.) by increasing activity of antioxidant enzymes

German chamomile is an important essential oil plant that has adaptability to a wide range of climates and soils. Methyl jasmonate (MJ) is a plant growth regulator that involves in many morphological and physiological processes and has a role in defense systems of plants under stress conditions. Here, a pot-culture study was undertaken to investigate the possible role of MJ treatment on the growth and different chemical constituents of German chamomile plants subjected to salinity stress. The aim was to determine whether MJ could protect chamomile production against salinity and whether this protection was associated with regulation of antioxidant enzymes. Our results show that treatment of chamomile plants with 75 µM MJ leads to increases in plant growth in terms of flower, straw and root dry weights. The photosynthetic rate concomitantly with membrane stability index, potassium content, as well as free proline content was markedly increased. In addition, the quercetin content was increased significantly in flowers. Moreover, the application of the investigated 75 μM MJ significantly improved enzyme activities in terms of catalase, peroxidase and ascorbate peroxidase activities. Sodium and proline contents were also measured and finally, effects of MJ and salinity interactions on all characteristics as well as relationship of antioxidant enzymes activity with proline content were investigated. As a conclusion, treating chamomile plants with 75 μM MJ could alleviate the harmful effects of salinity stress.