Recently, medicinal plant improvement for increase of secondary metabolites at cellular levels has gained an increasing attention. This study was conducted to optimize the mucilage production in Plantago ovata Forsk by employing different growth regulators, explants and genotypes. In the first experiment the callus induction and mucilage production by hypocotyl explants were assessed using different plant growth regulator treatments. Then the response of different explants (hypocotyl, seed and cotyledon) were examined to callus induction. In the third experiment the response of 14 different genotypes of Plantago ovata Forsk were assessed for callus induction and mucilage production. The most beneficial plant growth regulator combination for callus induction was assessed. Superior genotype was identified by evaluating callus induction (%), callus growth rate (mm/day) and the content of mucilage production in the calli. The results of analysis of variance showed significant differences between plant growth regulators on callus induction, callus growth rate and mucilage production by the calli. The callus induction rate varied from 76% (0.5 mgL -1 2,4D + 1 mgL -1 Kin) to 53% (2 mgL -1 2,4D + 1 mgL -1 Kin) for the most and the least desirable hormone combination, respectively. They yielded 0.382 (mm/day) and 0.167 (mm/day), respectively. The highest mucilage content (0.49 (g/g dry weight) was also produced at in ESF-1 genotype at 0.5 mgL -1 2,4D +1 mgL -1 Kin hormone combination. Interestingly, this treatment produced nearly three-fold higher mucilage content than that of the seeds in this genotype. Results of analysis of variance showed significant differences between evaluated explants for callus induction (%), callus growth rate and mucilage content. The highest callus induction (73%) and callus growth rate (0.33 mm/day) were observed in hypocotyl explant. Results of analysis of variance showed significant differences among genotypes for callus induction, callus growth rate and mucilage content. The highest (73%) and the lowest (55%) percent of callus induction were observed in ESF-1 and KHB genotypes, respectively. The highest callus growth rate 0.45 (mm/day) and lowest callus growth rate 0.21 (mm/day) were observed in ESF-1 and CHB genotypes, respectively. The highest mucilage content of the calli was 0.45 and the lowest one was 0.13 (g/g dry weight) and belong to ESF-1, and CHB genotypes, respectively. Key Words: Plantago ovata , psyllium, mucilage, explant, tissue culture .
