Phenotypic analysis of transgenic apple material under drought treatment. A) Representative images of calli. Bars = 1 cm. B) Fresh weight. C) SOD activity. D) CAT activity. WT, MdbHLH160-OE/RNAi transgenic calli were cultured on MS medium supplemented with 0 or 10% PEG6000 for 20 d. E) Growth phenotypes of transgenic apple plants after 20 d of drought treatment. Three replicates of 45 plants of each genotype were used for drought treatment. Scale bars represent 3 cm. F-G) RWC F) and REL G) in the leaves of apple plants. (H to M) Root vitality H), root hydraulic conductivity I), O₂⁻ content J), H₂O₂ content K), SOD activity L), and CAT activity M) in transgenic roots of apple plants. Samples were collected after 12 d of drought treatment to measure physiological parameters. Samples collected before drought treatment were used as controls. The data are presented as the means ± SD of 3 replicates. Different letters in B–D indicate significant differences based on 1-way ANOVA and Duncan's tests. Bars labeled with * in each panel are significantly different from the corresponding control plants (EV-OE/EV-RNAi) at P < 0.05 (Student's t-test).