There was no significant difference in the ratio of ABA and GA (ABA/GA) between plants grown at normal and low temperature Phenolic acids are first produced by PAL in the pathway of secondary metabolism and play a role in the protection of mesophyll cells against oxidative damage (Kling et al., 2014). As PAL activity decreased, the plants grown at low temperature under the long-day condition accumulated more phenolic acids than those grown at low temperature under the short-day condition (Table 2).