## 4 Discussion
Several pathways, including phenylpropane biosynthesis, isoquinoline alkaloid biosynthesis, and tyrosine metabolism, were found to be significantly enriched in differentially expressed genes (DEGs) of salt-tolerant quinoa (ST) under salt stress [51]. This study revealed significant differences in the regulation modes between 'LQ' and 'DT'. Dopamine and 3-(4-hydroxyphenyl) pyruvate were up-regulated in 'LQ' leaves under salt stress, while they were down-regulated in 'DT'. Exogenous dopamine treatment has been shown to effectively prevent cellular damage in tomato seedlings and increase plant salt tolerance, which aligns with our findings in 'LQ', suggesting that 'LQ' improved salt stress tolerance by enhancing the accumulation of these metabolites, thereby increasing its salt defense ability [52]. Gene expression analysis revealed that _AOC3_, _TAT_, and _GOT2_ were up-regulated in 'LQ', while these genes were down-regulated in 'DT', consistent with the metabolite changes, further suggesting that 'LQ' enhanced its defense capacity against salt stress by increasing the accumulation of these metabolites. 'LQ' may enhance its salt tolerance by intensifying isoquinoline alkaloid biosynthesis. Similarly, [PERSON] et al. reported that 191 genes were differentially expressed after KLBMP5084 treatment in tomato leaves under salt stress, with the highest enrichment of genes involved in the photosynthesis-antennal protein pathway and isoquinoline alkaloid biosynthesis, suggesting that these pathways may play important roles in responding to salt stress as well [53]. Although [PERSON] et al. [24] investigated the adaptation mechanisms of _A.__mongholicus_ under salt-alkali mixed stress, emphasizing the significant role of flavonoids in salt tolerance, the complexity of salt-alkali mixed stress complicates the attribution of physiological responses to individual stressors. The combined effects of NaCl and Na\({}_{2}\)CO\({}_{3}\), which induce both osmotic stress and pH alterations, often lead to ambiguous interpretations, complicating the identification of physiological responses attributed to each factor. In contrast, this study specifically focuses on NaCl single salt stress, providing a more refined and precise framework for examining plant response mechanisms. Recent studies have further underscored the importance of studying single salt stress in more detail. [PERSON] et al. [54] found that salt and alkali stress trigger distinct physiological responses in plants, suggesting that the independent investigation of each stressor may yield more accurate insights into their respective mechanisms. Similarly, [PERSON] et al. [55] demonstrated that alkali stress exerts a more significant inhibitory effect on oat growth compared to salt stress. Furthermore, [PERSON] et al. [56] pointed out the prevalent misinterpretation in the literature where salt-alkali stress is frequently simplistically referred to as salt stress, lacking scientific rigor due to the complex interaction between salinization and alkalization processes. Therefore, focusing on single salt stress offers a simplified but more accurate system, enabling a deeper understanding of critical pathways, such as phenylalanine metabolism and flavonoid biosynthesis. This approach is critical for elucidating mechanisms of salt tolerance, particularly in alleviating oxidative stress and regulating osmotic pressure. By concentrating on short-term salt stress, this study offers an innovative and focused exploration of salt tolerance mechanisms, bridging gaps left unaddressed by mixed salt-alkali stress studies. Overall, in this study, based on the salt stress phenotypic data of 20 _A.__mongholicus_ germplasms, salt tolerance was comprehensively evaluated using principal component analysis (PCA) and the affiliation function value, and the two germplasms with the strongest (LQ) and weakest (DT) salt tolerance were identified. The results showed that LQ significantly outperformed DT in terms of morphological development and biomass accumulation under 200 mmol/L NaCl stress.