Nutrient media and culture conditions
SH medium (Schenk and Hildebrandt 1972) supplemented with 1.0 mg l-1 TDZ, 0.3 mg l-1 NAA, 30 g l-1 sucrose (Luan et al. 2012) and agar (9.0 g l-1) as the solidified agent or other substrates (gelrite, filter paper, or cotton) was used as nutrient medium in this study. Medium for stem node elongation was SH supplemented with 0.5 mg l-1 NAA, 0.5 mg l-1 BA, 30 g l-1 sucrose, 9.0 g l-1 agar, and 1.0 g l-1 activated charcoal (AC). The pH was adjusted to 5.8 prior to the addition of AC and agar. After that, media were autoclaved at 121 C, 1 atm for 30 min. Explants were incubated in the darkness, or under a 16-h photoperiod with light intensity of 15–20 lmol m-2 s-1 of cool white fluorescent tubes, or 24-h photoperiod with light intensity of 5 lmol m-2 s-1 of LEDs depended on experiments.