## 3 Results  
### Effect of Exogenous ABA on Sophora vicifolia Seed Germination under Drought Stress Induced by PEG  
Exogenous ABA and PEG had significant effects on seed germination in _S. vicifolia_ (Tables 2 and 3). In the absence of ABA, the germination rate (GR), germination potential (GP), and germination index (GI) of _S. vicifolia_ seeds initially increased and subsequently decreased as the intensity of PEG-induced drought stress escalated. Specifically, at a 5% PEG-induced drought stress concentration, the GR, GP, and GI were all elevated in comparison to the control (CK). Conversely, at a 20% PEG-induced drought stress concentration, these metrics significantly diminished relative to CK (\(p<0.05\)). The introduction of ABA in varying concentrations distinctly influenced the seed germination under PEG-induced drought stress. At a 5% PEG-induced drought stress concentration, administering 50 mg\(\cdot\)L\({}^{-1}\) of ABA notably enhanced the GR, GP, and GI of _S. vicifolia_ seeds over the control (\(p<0.05\)), with increases of 1.632, 1.643, and 1.637 times, respectively, compared to CK. Furthermore, at a 20% PEG-induced drought stress concentration, treatment with 10 mg\(\cdot\)L\({}^{-1}\) and 50 mg\(\cdot\)L\({}^{-1}\) ABA significantly boosted the GR, GP, and GI relative to the control (\(p<0.05\)), marking enhancements of 15.333, 10.667, and 19.406 times, and 11.667, 3.667, and 14.016 times that of CK, respectively. This reveals that an optimal ABA concentration can mitigate the adverse effects of PEG-simulated drought stress on _S. vicifolia_ seed germination, thereby boosting their germination efficiency. Effect of Exogenous ABA on the Antioxidant Enzyme Activities in Sophora vicifolia under Drought Stress  
Exogenous ABA and PEG had significant effects on the activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) of _S. vicifolia_ (Figure 1 and Table 3). In the absence of ABA, POD and SOD in _S. vicifolia_ seedlings initially surged and then declined under the PEG-induced drought stress, while the activity of CAT progressively increased. Specifically, at 5% and 20% PEG-induced drought stress concentrations, the activities of POD and CAT significantly exceeded those of CK (\(p\) < 0.05), though SOD activity showed no significant variance from CK (\(p\) > 0.05). The introduction of ABA modulated the responses of SOD, POD, and CAT activities in the seedlings to the PEG-induced drought stress. As the ABA concentration increased across different PEG-induced drought stress, there was a corresponding enhancement in the activities of POD, CAT, and SOD (Figure 1). At a 5% PEG-induced drought stress concentration, the application of ABA at concentrations of 10 mg.L\({}^{-1}\), 50 mg.L\({}^{-1}\), 100 mg.L\({}^{-1}\), and 200 mg.L\({}^{-1}\) significantly fostered the activities of POD, CAT, and SOD (\(p\) < 0.05) compared to CK. The peak activities for SOD and CAT were observed at an ABA concentration of 100 mg.L\({}^{-1}\), whereas the apex of POD activity was noted at 200 mg.L\({}^{-1}\) ABA. In conditions of 20% PEG-induced drought stress concentration, varying concentrations of ABA markedly elevated the activities of POD, CAT, and SOD relative to the control (\(p\) < 0.05), with the maximal activities of POD and SOD recorded at an ABA concentration of 200 mg.L\({}^{-1}\) and the highest CAT activity observed at 100 mg.L\({}^{-1}\) ABA. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Index**} & **PEG-6000** & \multicolumn{4}{c}{**ABA Concentration (mg.L\({}^{-1}\))**} \\ \cline{3-6}  & **Concentration** & **0** & **10** & **50** & **100** & **200** \\ \hline \multirow{2}{*}{ \begin{tabular}{c} Germination rate \\ (GR) \\ \end{tabular}