In order to study the effects of five levels of water stress (0, -2, -4, -6 and -8bar) on germination characteristics and seedling growth of two medicinal plants (Hyssopus officinalis L. and Chrysanthemum x superbum Bergmans ex J.Ingram), two experiments were conducted at physiology laboratory of Faculty of Agriculture Ferdowsi University of Mashhad as a Completely Randomized Design with four replications. The results showed that the effects of different levels of water stress were significant in all of the studied characteristics of two plants. Germination percentage was decreased and mean germination time were increased by increasing in water stress levels and, germination percentage was zero in levels of -6bar in two types of plants. It is suggested that decrease in seed germination and depression in seedling growth under drought conditions related to limited hydrolysis of food reserves from storage tissues as well as due to impaired translocation of food reserves from storage tissue to developing embryo axis [3]. Root length of Hyssop and Marguerite respectively, were increased and decreased by increasing in water stress levels. Plumule length had a decreasing trend in two studied plants, but amounts of this trend was less in hyssop and the root length/plumule length were increased in each of plants. Many researchs were shown that an increased root/shoot ratio resulting in more efficient water and nutrient uptake [1,2]. Also, dry weight root had increased trend and dry weight plumule had decreasing trend but root dry weight/plumule dry weight was increased in two types of plants.

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