3.4 Overexpression of MdASMT9 increased soluble sugar and amino acid levels in apple leaves under heat stress
The tolerance of plants to heat stress is related to the accumulation of soluble carbohydrates and amino acids. Therefore, the soluble sugar and amino acid content in WT and MdASMT9 -OE lines were also measured. The transgenic lines showed a great increase in the galactose, sorbitol, and sucrose contents compared to the WT (Figure 4A-C). Meanwhile, the contents of the measured amino acids (histidine, arginine, aspartate, proline, glutamine, and glycine) significantly increased inMdASMT9 -OE lines, allowing them to better withstand heat stress (Figure 4D-I). For example, the OE-3 and OE-4 lines exhibited about 3.2 and 2.5 times greater histidine levels than the WT, respectively (Figure 4D). The arginine contents in MdASMT9 -OE plants were approximately 2.3 times greater than those in the WT after exposure to 48°C for 8 h (Figure 4E).