Increasing bioactive compound levels in Agastache rugosa by hydrogen peroxide soaking in a hydroponic culture system

Abstract

Hydrogen peroxide (H2O2) is a reactive oxygen species that can damage a variety of cellular structures. Recent studies have shown that H2O2 can mediate multiple physiological and biochemical processes by acting as a signaling molecule. This study was performed to explore the optimum H2O2 treatments for increasing the bioactive compounds in Agastache rugosa Fisch. & C.A. May plants with roots temporarily immersed in H2O2 concentrations of 0 (control), 4, 8, 16, 32, 64, and 128 mmol L−1 in a hydroponic culture system. All cultivated plants were subjected to root soaking with diniconazole (120 μmol L−1) at 7 days after transplanting to restrict plant height. H2O2 concentrations of 4, 16, and 64 mmol L−1 significantly reduced root length compared with no H2O2 treatment. Root fresh weight was significantly lower in response to exposure to 128 mmol L−1 H2O2 compared with control plants. Although shoot and root dry weights were lower in plants exposed to 128 mmol L−1 H2O2 compared with control plants, no significant differences were detected among treatments. Soaking roots in 16 mmol L−1 H2O2 induced the highest rosmarinic acid (RA) content, and 16, 32, and 64 mmol L−1 H2O2 significantly increased tilianin content in the whole plant compared with the control. The highest acacetin content was detected under 32 mmol L−1 H2O2. In addition, root extract of A. rugosa had the highest RA concentration, and the tilianin concentration was the highest in flowers. Collec-tively, these results show that soaking roots in 16 and 32 mmol L−1 H2O2 at 3.5 weeks after transplanting promotes secondary metabolites of hydroponically grown A. rugosa.