DOI: 10.32615/bp.2019.020 BIOLOGIA PLANTARUM 63: 174-182, 2019 174 This is an open access article distributed under the terms of the Creative Commons BY-NC-ND Licence Meta-topolin improved micropropagation in Syzygium cumini and acclimatization to ex vitro conditions A. NAAZ 1,3 , S.A. HUSSAIN 1 , M. ANIS 1 *, and A.A. ALATAR 2 Plant Biotechnology Laboratory , Department of Botany, Aligarh Muslim University, Aligarh 202002, India 1 Department of Botany and Microbiology, Faculty of Science, King Saud University, Riyadh 11451, Saudi Arabia 2 Department of Physics, Indian Institute of Technology, Patna 801103, India 3 Abstract An efficient micropropagation system was developed for a recalcitrant woody tree Syzygium cumini (L.) Skeels using nodal explants excised from 15-d-old aseptic seedlings. The explants were employed on an Murashige and Skoog (MS) medium supplemented with different concentrations (1.0 - 10.0 μM) of cytokinins, such as benzyladenine (BA), kinetin (Kin), meta-topolin (mT), or 2-isopentyl adenine (2ip), either alone or in combination with different concentrations (1.0 - 3.0 μM) of auxins, such as indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), or α-naphthalene acetic acid (NAA). Of the cytokinins tested, mT proved to be best for shoot bud induction and proliferation. Among the tested combinations, a maximum regeneration (90 %) with a mean shoot number of 25.33 ± 0.33 and a shoot length of 5.20 ± 0.11 cm were recorded on the MS medium containing 5.0 μM mT + 2.0 μM NAA after 12 weeks of incubation. Further 4-week incubation on optimum 5.0 μM mT before transfer to a secondary medium consisting of MS + 5.0 μM BA + 2.0 μM NAA yielded up to 51 microshoots with an average length (6.53 cm). For in vitro rooting, healthy shoots (about 5 cm) were excised and incubated on the half or full strength MS medium enriched with different concentrations (1 - 7.5 µM) of NAA. A substantial increase in rhizogenic competency (15 %) was observed in shoots raised on a medium with mT with a mean root number of 6.33 ± 0.10 and a mean length of 5.13 ± 0.21 cm on the half MS supplemented with 5.0 µM NAA after 4 weeks. A maximum of 95 % plantlets regenerated on the medium with mT was successfully acclimatized and established in earthen pots under field conditions. The consistent increases in activities of superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase during acclimatization indicate that mT raised plantlets response well to the stress induced by ex vitro conditions. Additional key words: ascorbate peroxidase, benzyladenine, catalase, glutathione reductase, α-naphthalene acetic acid, superoxide dismutase. Introduction Syzygium cumini L. (Myrtaceae) is a valuable medicinal tree commonly known as jamun in the Indian subcontinent. It is a rich source of bioactive compounds like alkaloids, flavonoids, sterols, saponins, tannins, and volatile oils. The tree is naturally propagated through seeds, but poor seed viability, low germination rate and fast fungal contamination on germinating seeds restrict the production of healthy plant stocks. Micropropagation of this recalcitrant species has been reported earlier through juvenile (Yadav et al. 1990, Jain and Babbar 2000, Rathore et al. 2004) and mature tissues (Naaz et al. 2014). Continuous research in plant tissue culture  Submitted 10 April 2018, last revision 17 August 2018, accepted 1 October 2018. Abbreviations: APX - ascorbate peroxidase; BA - benzyladenine; CAT - catalase; GR - glutathione reductase; IAA - indole-3-acetic acid; IBA - indole-3-butyric acid; 2ip - isopentyl adenine; Kin - kinetin; MDA - malondialdehyde; mT - meta-topolin; MS - Murasige and Skoog; NAA - α-naphthalene acetic acid; PGR - plant growth regulator;SOD - superoxide dismutase. Acknowledgements: The authors extend their appreciation to the International Scientific Partnership Program (ISPP) at King Saud University for funding this project (ISSPP # 0082). The award of the UGC-BSR Faculty Fellowship (2017) to M.A. is duly acknowledged. A.N. gratefully acknowledges the financial assistance provided by the Science and Engineering Research Board (SERB)/Department of Science and Technology Govt. of India, New Delhi, India, for the award of National Post-doc Fellowship (NPDF) vide PDF/2016/003254. * Corresponding author; e-mail: anism1@rediffmail.com