## 4 Discussion
### Enzyme Activity  
The key enzyme of phenyl alanine-lyase is included in the biosynthesis of phenolics such as flavonoids and phenols [66]. Previous studies showed that the high amounts of phenols and anthocyanins in apple and grape fruits resulted in an increased the level of PAL [67; 68]. In this study, MeJA-treated fruits showed higher TAC and PAL activity compared to the water-treated fruits (Figures 1 and 2). These results indicate that antioxidant capacity increased by MeJA may also induce PAL activity, thus promoting phenolic metabolism. This result agrees with the studies of [PERSON] and [PERSON] [26]. [PERSON] et al. [27] and [PERSON] et al. [58] also demonstrated that MeJA increased the activity of PAL in fruits of sweet cherry, peach and pomegranate. In the case of SA, two studies [26; 69] reported that SA had an essential role in systematic acquired resistance (SAR) induction by promoting defense and antioxidant enzymes such as PAL, which was also supported by our results in apricot fruit. increasing the activities of PAL and POD and the lignin content in fruit resulting in a higher firmness and a lower weight loss. In addition, induction of systemic resistance to biotic or abiotic stresses can lead to direct activation of defense-related proteins. POD has an essential role in the structure components of cell walls and lignin formation. An increase in POD activity was reported for SA-treated (4 mM) mandarin fruit which was related to low FD [70]. Previous studies, e.g., [26; 71; 72], and this study also confirmed that either MeJA or SA treatment increased POD activity and decreased fruit decay (Figure 2; Table 1). The SOD enzyme has several roles in plant cells, such as detoxifying ROS and lowering chilling injury [73; 74]. SOD activity was high in chilling tolerant mandarin fruit during CS at 2.5 \({}^{\circ}\)C for 8 weeks [73]. Previous studies e.g., [23; 24; 75] showed that MeJA significantly increased the activity of SOD in loquat, peach and strawberry fruit in the storehouse compared to the control treatments, while [PERSON] et al. [64] showed a similar effect of SA treatment for orange fruit. Our apricot study was in agreement with the above previous studies on SA or MeJA results on SOD activity. However, here we provided for the first time a comparison between MeJA and SA treatments on SOD activity which showed that SOD activity was generally higher in the MeJA treatments than in the SA treatments. CAT is a key enzyme in the catalyzation of H\({}_{2}\)O\({}_{2}\) into H\({}_{2}\)O and O\({}_{2}\), and therefore it has a function to remove active oxygen species (AOS) from the cell during stress [64]. In agreement with our results, MeJA was reported to maintain high CAT activity in strawberry plants [75] and in loquat fruit during the CS period [23] compared to non-treated fruit. However, SA treatment's effects on CAT activity were not uniform in previous studies. [PERSON] et al. [64] showed that SA pretreatment reduced CAT activities compared to the non-treated fruit. However, similarly to our apricot study, [PERSON] et al. [76] demonstrated that SA treatments increased CAT activity in apple fruit compared to the non-treated control. This might be associated with the result of the study of [PERSON] et al. [77] that SA can increase the CAT gene activity, i.e., the transcription and translation. In addition, not only CAT, but also ascorbate peroxidase is a key enzyme of fruits in the removal of H\({}_{2}\)O\({}_{2}\). Although this peroxidase was not investigated in this study, future data on ascorbate peroxidase activity also contribute to the better understanding of the mechanism of the antioxidant capacity and of the defense systems involved. No previous fruit studies investigated correlations among enzyme activity parameters for MeJA and SA jointly under postharvest treatments.