Enhanced callus induction and high-efficiency plant regeneration in Tribulus terrestris L., an important medicinal plant

We described culture conditions for direct and indirect regeneration of Iranian Tribulus terrestris L. through epicotyl, hypocotyl and leaf explants. The explants were cultured on MS medium supplemented with different concentrations and combinations of auxin and cytokinin. The results indicated that the mean of callus induction was influenced by explant type and various phytohormones levels. The highest percentage of callus production occurred on MS medium containing 0.1 mg/l naphthalene acetic acid (NAA) and 1 mg/l 6-benzylaminopurine (BAP) from epicotyl explants (91.6%), 0.4 mg/l (NAA) + 2 mg/l (BAP) from hypocotyl explants (94.3%), and 0.4 mg/l (NAA) + 0.5 mg/l (BAP) for leaf explants (100%). Efficient shoot regeneration (22%) was achieved when the epicotyl explants were incubated on MS media amended with 0.1 mg/l (NAA) + 2 mg/l (BAP) and 0.4 mg/l (NAA) + 0.5 mg/l (BAP) within 14 days of culture. Maximum indirect shoot regeneration (28.4%) was achieved from green-yellowish calli derived hypocotyl explants on MS medium with 0.4 mg/l (NAA) + 2 mg/l (BAP) within 21 days of culture. Also, an in vitro regeneration system from nodal segments was developed on MS medium supplemented with different levels of 6-benzyladenine. Maximum number of shoots per nodal explants was developed on a medium containing 3 mg/l (BA) at the rate of 2.5 micro-shoots per nodal explants after 4 weeks of culture. Proliferated shoots were elongated in hormone-free MS medium and also, shoots were rooted on MS medium and MS with 2 mg/l indol-3-butyric acid.   Key words: Tribulus terrestris, plant regeneration, callus induction, plant growth regulators, MS (Murashige and Skoog) medium.