Physiological response of medicinal plant, marjoram (Origanum majorana) to methyl jasmonate in drought stress conditions

Marjoram (Origanum majorana L.) is one of the plants of Labiatae family. Drought stress limits the growth of medicinal plants, including marjoram. In this study, response of marjoram to foliar methyl jasmonate application (with concentrations 0, 100 μM) under drought stress (soil moisture equivalent to 50 (moderate stress), 75 (mild stress) and 100% of field capacity (without stress)) was evaluated. Based on the results obtained in this study the effect of different levels of drought stress on plant fresh and dry weight, plant height, chlorophyll b, total chlorophyll and carotenoids content, catalase activity and soluble sugar content was significant. When compared to control, moderate stress reduced chlorophyll and increased carotenoids, catalase activity and soluble sugar content 15.52, 38.25, 79.63 and 42.86% respectively. Essential oil percentage, which obtained from plant leaves under drought stress, did not change significantly. Application of methyl jasmonate increased chlorophyll a, b and total, catalase activity and soluble sugar, particularly in non- stress and severe stress conditions. These results showed that methyl jasmonate could increase catalase activity and soluble sugar content while under drought stress condition inhibit the activity of free radicals and thus ensures survival of the marjoram plants. In general, the results of this experiment showed that the use of mthyl jasmonate could appropriate way to cope with drought in marjoram.