3.2 Overexpression of MdASMT9 stimulated ROS scavenging
under heat stress
High levels of ROS, such as H2O2 and
O2−, can damage macromolecules and
membrane lipid structures, leading to oxidative damage with deleterious
effects on plants (Mittler et al. , 2011). Therefore, we stained
the leaves with 3,3’-diaminobenzidine (DAB) and nitro blue tetrazolium
(NBT) separately to detect H2O2 and
O2–, accumulation, respectively. Results showed that
heat stress caused ROS accumulation in all genotypes; however,MdASMT9 -OE lines exhibited fewer brown areas and blue spots on
their leaves compared to the WT plants (Figure 2A). Quantitative
measurements of H2O2 and
O2– were consistent with these observations, showing
that after 8h of heat treatment, the MdASMT9 -OE lines had lower
ROS levels than the WT plants (Figure 2B and 2C). Moreover, activities
of antioxidant enzymes (SOD, CAT, and POD) were quantified. Exposure to
48°C for 8h increased SOD, POD, and CAT activities, with OE-3 and OE-4
exhibiting a greater increase than WT plants (Figure 2D-F). These
findings indicate that MdASMT9 -OE apple plants showed less
oxidative damage than WT plants when exposed to high-temperature stress.