## 4 Discussion  
Salt stress exerts significant effects on plant growth and development [24; 28]. Excessive salinity in the soil typically results in the accumulation of NaCl, which, in turn, impairs plant water uptake and nutrient absorption, ultimately leading to growth retardation and even plant death [29]. Under salt stress, the plant cell membrane structure becomes disrupted, leading to a dysregulation of ionic balance that triggers an excessive accumulation of reactive oxygen species (ROS) [30]. POD, SOD, and CAT play an essential role in maintaining cellular ROS homeostasis when ROS content increases significantly in plants, causing oxidative damage to cells [31]. Regarding enzyme resistance systems, POD, SOD, and CAT showed significant increases after salt stress was applied to the two _A.__mongholicus_ germplasms in this study. Notably, antioxidant enzyme activity levels in 'LQ' were higher than those in 'DT' after salt stress, indicating that the salt-tolerant germplasm exhibited strong ROS scavenging ability and mitigated ROS-induced cellular damage under  
Figure 15: Isoquinoline alkaloid synthesis pathway. salt stress conditions. Furthermore, the MDA content in 'LQ' was significantly lower than that in 'DT' under salt stress treatment. Similar results have been previously observed in spring wheat [32]. In this study, the trends of proline, soluble sugars, and soluble protein contents were consistent with those of antioxidant enzyme activities, suggesting that the plants effectively maintained cellular osmotic pressure and enhanced salt tolerance by accumulating osmoregulatory substances. Both osmoregulatory substances and antioxidant enzymes alleviated salt stress toxicity in _A.__mongholicus_ seedlings to some extent, which is consistent with results from studies on marigold [33], magnolia [34], and sorghum [35] under salt stress. However, in addition to the role of enzymatic antioxidants, non-enzymatic antioxidant systems also play equally crucial roles in the plant's response to salt stress in _A.__mongholicus_ species. For instance, flavonoids are key secondary metabolites that are widely implicated in the plant's response to abiotic stress. Certain plants improve their salt tolerance by accumulating elevated levels of flavonoids [36]. In this study, the levels of apigenin and neohesperidin were significantly increased in 'LQ' following salt treatment, while several key genes involved in the flavonoid biosynthetic pathway (_CHS_, _F3H_, and _CYP5A_) showed significant up-regulation in expression, consistent with previous findings in Lonicera [37]. The trend was further validated by qRT-PCR analysis, which revealed significant up-regulation of the _CHS_, _F3H_, and _CYP5A_ genes under salt stress, along with a consistent up-regulation trend for the Cluster-33548.11 gene in the _CHS_ family. The 'DT' germplasm exhibited down-regulation of apigenin and neohesperidin, further suggesting that the spatial and temporal expression patterns of the associated genes in the flavonoid biosynthetic pathway are closely linked to the plant's salt stress response. In recent years, several studies have confirmed the anti-salt effect of apigenin. [PERSON] et al. showed that apigenin pretreatment induced an antioxidant defense system in rice seedlings, evidenced by increased activities of catalase (CAT) and ascorbate peroxidase (APX) in the root system, as well as enhanced accumulation of carotenoids and flavonoids in the shoots. Additionally, apigenin modulated the selective uptake and transport of ions by the roots, maintaining the antioxidant defense system in the root, as well as enhancing the selective uptake and translocation of ions in the roots to maintain a high K+/Na+ ratio, a crucial property for plant growth under salt stress [38]. This enhanced antioxidant capacity not only mitigates oxidative damage by scavenging ROS but may also enhance salt tolerance by increasing the activities of antioxidant enzymes (e.g., SOD, POD, and CAT), consistent with the results of our physiological studies.