Transcriptomic response of apple (Malus x domestica Bork. cv. Húsvéti rozmaring) shoot explants to in vitro cultivation on media containing thidiazuron or 6-benzylaminopurine riboside

The effects of two cytokinins (thidiazuron and 6-benzylaminopurine riboside), each applied at 4.5 μM, were studied on mRNA transcription of in vitro apple shoots. Transcriptomic response was investigated at two time points; at 48 h and 4 weeks (end of the subculture) after the cytokinin application 20-mm-long shoot explants from in vitro maintained shoot cultures of apple (Malus x domestica Borkh. cv. Húsvéti rozmaring) were used as the source for the experiments. In vitro shoots served as explant source were maintained on MS (Murashige and Skoog, 1962) medium supplemented with 2.22 μM 6-benzylaminopurine (BA), 0.49 μM indole butyric acid (IBA), 0.58 μM gibberellic acid (GA3), 3% (w/v) sucrose, and 0.7% (w/v) agar-agar. ). Before autoclaving for 20 min, at 121 °C and 105 Pa, the pH of the medium was adjusted to 5.8. Each culture vessel contained 70 ml of medium and five shoot explants. Shoot cultures were grown at 23±2 °C; under 16/8 photoperiod, at light intensity of 106 µmol s-1 m-2. However, in the last subculture before the experiments, shoots were grown in vitro on cytokinin-free medium to avoid the after-effects of cytokinin in the experiments. 4-week-old in vitro shoots grown on cytokinin-free medium were separated from in vitro mother shoots, cut into 20-mm-long segments and placed on experimental media. Except for the cytokinin content, the experimental media were the same as the medium used for maintenance described above. Three different cytokinin-containing media were used during the experiments; medium without cytokinin (control), media containing 4.5 μM thidiazuron (TDZ) and 4.5 μM 6-benzylaminopurine riboside (BAR), respectively.