Dianthus barbatus is an important ornamental bedding plant in temperate regions with traditional medicinal applications. Water shortage and drought stress are major limitations for landscape development and plant medicine production. Callogenesis is the key step for modern plant breeding techniques and in vitro drought stress study defines the mechanisms of plant response to stress. Therefore this research focused on a) callogenesis optimization by different explants (leaf, stem and root) and plant growth regulators (BAP, NAA and 2,4-D) and b) effect of osmotic stress (-1, -3, -6, -9 and -12 bar) induced by polyethylene glycol on D. barbatus calli. For callogenesis optimization, various criteria such as callogenesis percentage, calli colour, tissue type and growth besides chlorosis and necrosis were observed. In the second part, total protein and glycine-betaine content besides the activity of some free radical scavenger enzymes such as superoxide dismutase, catalase, peroxidase were also measured during stress at various levels. Results indicate leaf as the most suitable explant and both 2µM BAP + 4µM NAA and 2µM BAP + 6µM NAA as the most suitable media supplements for callogenesis. As calli were subjected to osmotic stress, growth and weight of stressed calli decreased by osmotic stress increment. As osmotic pressure decreased (osmotic stress increased), total protein content decreased while glycine-betaine osmolyte increased. The activity of some free radical scavenger enzymes such as superoxide dismutase, catalase, peroxidase also increased by osmotic stress increment.

Keywords: BAP, Catalase, Drought stress, Glycine- Betaine, NAA, Peroxidase, Poly Ethylene Glycol, Superoxide dismutase.

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