Interaction of nutrients, pH and osmotic potential of culture medium on calli induction ‎‎and embryogenesis of Paulownia tree in vitro

Paulownia is a fast-growing, industrial and ornamental tree with medicinal properties. The present study was performed to investigate the osmotic potential of MS basal culture medium under the effect of macronutrients and micronutrients. Also, the effect of osmotic potential on callus induction, somatic embryo, regeneration, antioxidant activity and somaclonal variation were investigated. The present experiment was carried out factorial in a completely randomized design with two factors, explants (leaves and petioles) and eight types of culture media containing different combinations of culture medium elements with different combinations of plant growth regulators (PGR). The results showed that the highest level of callus induction, somatic embryogenesis and regeneration were observed in media with one-half and one-quarter times the macronutrients of MS culture medium. Anthocyanin activity, chlorophyll content, embryo number and osmotic potential increased with decreasing macronutrients, especially nitrate sources in culture medium. However, callus growth rate and somaclonal variation decreased. In culture medium, calluses and embryogenic calluses without burns, transparent, regenerated seedlings were more vibrant and the most pigments were observed in the leaves of seedlings. In complete MS media, callus induction, somatic embryo, osmotic potential, anthocyanin, chlorophyll decreased. While callus growth rate and somaclonal variation increased.