Licorice (Glycyrrhiza glabra L.), is one of the herbal medicines and glycyrrhizin is the most important chemical content through compounds exiting in licorice, which is 50 times sweeter than sucrose. Drought stress is one of the limiting factors of growth and development of the plants having negative impacts on morphological and physiological processes in plants. In order to investigate the effects of different levels of drought stress on some growth, physiological and biochemical characteristics of two genotypes of licorice, an experiment was conducted in field as a factorial experiment based on randomized complete block design with three replications. Experimental treatments included different levels of drought stress (control, 10, 20 and 30 days) and different genotypes of licorice (Chaharmahal_Bakhtiari and Ilam). The studied parameters such as: dry weights roots and fresh weights of shoot, relative water content (RWC), chlorophyll a (Chlα), chlorophyll b (Chlb), total chlorophyll, carotenoid, antioxidant activity, total phenol content, ascorbate peroxidase (ASP) and glycyrrhizin content were investigated in this study. The results showed that, the root dry weight, shoot fresh weights, RWC, Chlα, Chlb, total chlorophyll and carotenoids were decreased significantly under drought stress. The highest antioxidant and ASP activity 88.85% and 4/4 absorbance changes in mg of protein, respectively, were recorded in Ilam genotype in intense stress. Also, the highest amount of total phenol was observed in Ilam genotype in moderate stress (59 mg Gallic acid per 100 g) and the maximum content of glycyrrhizin was observed in genotype of Chaharmahal and Bakhtiari genotype under mild stress (2.97%). In general, the morphological traits and antioxidant properties of Ilam genotype were higher than Chaharmahal_Bakhtiari. However, in terms of photosynthetic pigments and glycyrrhizin content, genotype of Chaharmahal_Bakhtiari was higher than Ilam. It seems totally, regarding to the antioxidant content the Ilam genotype is superior to Chaharmahal_Bakhtiari in drought tolerant.

Keywords: Antioxidant, drought stress, photosynthetic pigments, licorice, glycyrrhizin, filed

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