2.1 Plant materials and growth conditions
In vitro shoot cultures of Malus domestica ‘GL-3’ (‘Royal Gala’) wild type (WT) and MdASMT9 -OE apple lines (OE-3 and OE-4) were cultivated as described previously (Zhou, Li, et al. , 2022). After the tissue-cultured seedlings developed roots, the WT andMdASMT9 -OE lines were transplanted into pots filled with a loam-perlite mixture in a 1:1 ratio (by volume). The plants were grown in a greenhouse with a light/dark cycle of 16 h/8 h at 24 °C temperature for a duration of eight weeks.