2.1 Plant materials and high-temperature treatment
In vitro shoot cultures of Malus domestica ‘GL-3’ (‘Royal Gala’) and two MdASMT9 -OE lines were cultivated as described previously (Zhou et al. , 2022). After culturing on rooting medium, WT andMdASMT9 -OE plants were transplanted to pots containing a 1:1 (by volume) loam-perlite mixture and grown in a growth chamber with a 16h-light/8h-dark cycle at 24°C. For the heat treatment, 2-month-old apple plants were exposed to a 48°C for 8 h.