*2.2. Culture Media and Growth Condition*

The sterile shoot segments were grown in nutritional medium that included various concentrations and combinations of growth regulators. Murashige and Skoog [56] plant cell culture basal medium (MS; M5519, Sigma-Aldrich, Inc., St. Louis, MO, USA) was used in all assays; it was composed of macro and micro-salts, vitamins, 3 percent (*w*/*v*) sucrose (AppliChem GmbH, Darmstadt, Germany), and 0.8 percent (*w*/*v*) agar-agar (Avonchem Ltd., Wellington House, Cheshire, UK) and had a pH of 5.7. The pH of the MS basal was adjusted with 1 N aqueous solution of NaOH or HCl before steam sterilization in an ALP-autoclave (CLG-32L, ALP Co., Tokyo, Japan) for 20 min at 121 ◦C (15 psi). In a growth chamber (Conviron Adaptis-CMP6010, USA), all the cultured vials were incubated under 50 μmol m−<sup>2</sup> s−<sup>1</sup> l light illuminance provided by Philips 39-Watt T5 linear fluorescent tubes (F39T5/841/HO/ALTO, Philips, Amsterdam, The Netherlands) with a day–night photoperiod of 16/8 h and a temperature of 24 ± 2 ◦C.

## *2.3. Growth Regulators, Shoot Induction, and Proliferation*

For shoot induction and proliferation, the sterilized nodal sections of *P. amboinicus* were cultivated on MS medium supplemented with 0, 0.5, 2.5, 5.0, 7.5, and 10.0 μM of 6-benzyladenine (BA; Duchefa Biochemie B.V., Haarlem, The Netherlands) or kinetin (Kin; Sigma-Aldrich Chemicals Co., MO, USA) at different concentrations, either individually or in combination with 0, 0.1, 0.5, 2.5., and 5.0 μM of auxins such as indole-3-acetic acid (IAA; Duchefa Biochemie B.V., Haarlem, The Netherlands) or α-naphthalene acetic acid (NAA; Duchefa Biochemie B.V., Haarlem, The Netherlands). The effects of the strength of the MS basal medium (one-quarter; one-third; half; and full strength) and various pH levels (4.7, 5.2, 5.7, and 6.2) on the in vitro morphogenic response of *P. amboinicus* nodal sections were also evaluated using optimum phytohormonal combinations and concentrations of BA (5.0 μM) and NAA (2.5 μM). In order to achieve a higher number of shoots from each nodal section, the responding plant materials were sub-cultured onto the fresh media every three weeks. After 8 weeks of in vitro growth and proliferation, data on the percentage of the explants' regeneration as well as the number of axillary shoots per explant were recorded.
