Preparation of plant extracts
For both tissue culture and acclimatized experiments, the plantlets were separated into aerial and underground parts, freezedried materials and lypholized. In a 2 mL Eppendorf, the ground materials (100 mg mL−1) were homogenized with 80% methanol using an oscillation ball mill (MM 301, Retsch, Haan, Germany) at a frequency of 27 1/s for 3 min. The resultant extracts were centrifuged for 10 min at 20,000 rpm and the supernatant was retained for subsequent analysis.