Effect of drought stress on the activity of some antioxidant enzymes and total soluble proteins of thyme (Thymus vulgaris L.)

Thyme is one of the most important medicinal plants which grows naturally in wide areas of range lands in Iran and simultaneously is cultured widely in Iran and other parts of the world. As Iran has placed in arid and semi-arid regions of the world, with actually low precipitation, doing projects in order to reveal the mechanisms or increase the drought tolerance of crop and medicinal plants has great value. Drought stress decreases the yield and quality of medicinal plants as well as crops. To investigate the mechanisms of drought tolerance of thyme plants and to evaluate the possibility of increasing of drought tolerance in these valuable medicinal plants, activity of some antioxidant enzymes and total soluble proteins were been analyzed in Thymus vulgaris L.in a complete randomized design experiment. After reaching to the adequate stage of growth, seedlings were grown in pots containing suitable soil, were subjected to different levels of drought stress (80% as control, 60% and 40% irrigation of field capacity(FC) as treatments). Results show that, drought stress had significant effect on total protein content as well as the activity of antioxidant enzymes. At 60% FC treatment and especially at 40% FC the amount of total soluble proteins drastically decreased. However; the activity of catalase increased at 60% FC treatment. The activity of peroxidase did not change significantly at 60% treatment but its activity decreased at 40% treatment. As a conclusion; it can be suggested that, one of the drought tolerance mechanisms of thyme is increasing of the activity of antioxidant enzymes especially the activity of catalase.