Optimization of salicylic acid concentrations for increasing antioxidant enzymes and bioactive compounds of Agastache rugosa in a plant factory.

Salicylic acid (SA) plays a crucial role as a hormone in plants and belongs to the group of phenolic compounds. Our objective was to determine the optimal concentration of SA for enhancing the production of bioactive compounds in Agastache rugosa plants while maintaining optimal plant growth. The plants underwent SA soaking treatments at different concentrations (i.e., 0, 100, 200, 400, 800, and 1600 µmol mol-1) for 10 min at 7 days after they were transplanted. We observed that elevated levels of SA at 800 and 1600 µmol mol-1 induced oxidative stress, leading to a significant reduction across many plant growth variables, including leaf length, width, number, area, shoot fresh weight (FW), stem FW and length, and whole plant dry weights (DW) compared with that in the control plants. Additionally, the treatment with 1600 µmol mol-1 SA resulted in the lowest values of flower branch number, FW and DW of flowers, and DW of leaf, stem, and root. Conversely, applying 400 µmol mol-1 SA resulted in the greatest increase of chlorophyll (Chl) a and b, total Chl, total flavonoid, total carotenoid, and SPAD values. The photosynthetic rate and stomatal conductance decreased with increased SA concentrations (i.e., 800 and 1600 µmol mol-1). Furthermore, the higher SA treatments (i.e., 400, 800, and 1600 µmol mol-1) enhanced the phenolic contents, and almost all SA treatments increased the antioxidant capacity. The rosmarinic acid content peaked under 200 µmol mol-1 SA treatment. However, under 400 µmol mol-1 SA, tilianin and acacetin contents reached their highest levels. These findings demonstrate that immersing the roots in 200 and 400 µmol mol-1 SA enhances the production of bioactive compounds in hydroponically cultivated A. rugosa without compromising plant growth. Overall, these findings provide valuable insights into the impact of SA on A. rugosa and its potential implications for medicinal plant cultivation and phytochemical production.

Effectiveness of silver nitrate application on plant growth and bioactive compounds in Agastache rugosa (Fisch. & C.A.Mey.) kuntze.

The objective of this study was to determine the optimal dose of silver nitrate (AgNO3) for plant growth and to increase the main bioactive compounds in A. rugosa cultivated in a hydroponic system. The application of soaked diniconazole (120 µmol mol-1) to all plants at 7 days after transplanting (DAT) for dwarfing plant height, optimizing cultivation space in the plant factory. Subsequently, plants were soaked with 50, 100, 200, and 400 µmol mol-1 AgNO3 for 10 min at 25 DAT and harvested at 39 DAT. The results indicated that 200 and 400 µmol mol-1 treatments tended to severely decrease plant growth parameters compared to treatments with lower concentrations. The net photosynthetic rate was significantly reduced by the 200 and 400 µmol mol-1 treatments compared to treatments with other concentrations. The 400 µmol mol-1 treatment led to the lowest concentrations of chlorophyll a, chlorophyll a/b, total carotenoid, chlorophyll b, and the total chlorophyll. However, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was considerably increased in 50, 100, 200, and 400 µmol mol-1 compared to that of the control plants. A higher rosmarinic acid (RA) concentration in the whole plant was noticed with the 400 µmol mol-1 treatment compared with that of the untreated plants. The 100 µmol mol-1 treatment exhibited the highest concentration and content of tilianin in the whole plant. Concentration of acacetin 1 significantly increased in the whole plant with 100 and 200 µmol mol-1 treatments compared with that of the untreated plants. Concentrations of acacetin 2 and 3 in the whole plant were the highest with 100 and 200 µmol mol-1 treatments, respectively. The results demonstrated that 100 µmol mol-1 treatments can be used to increase bioactive compounds without severely limiting the plant growth and reducing chlorophyll concentrations of A. rugosa. Implementing this optimal dose can enable growers and researchers to cultivate A. rugosa more efficiently, enhancing bioactive compound content and overall plant performance, thus harnessing the potential health benefits of this valuable plant species.