Increasing bioactive compound levels in <i>Agastache rugosa</i> by hydrogen peroxide soaking in a hydroponic culture system

Hydrogen peroxide (H 2 O 2 ) is a reactive oxygen species that can damage a variety of cellular structures. Recent studies have shown that H 2 O 2 can mediate multiple physiological and biochemical processes by acting as a signaling molecule. This study was performed to explore the optimum H 2 O 2 treatments for increasing the bioactive compounds in Agastache rugosa Fisch. &amp; C.A. May plants with roots temporarily immersed in H 2 O 2 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. H 2 O 2 concentrations of 4, 16, and 64 mmol L −1 significantly reduced root length compared with no H 2 O 2 treatment. Root fresh weight was significantly lower in response to exposure to 128 mmol L −1 H 2 O 2 compared with control plants. Although shoot and root dry weights were lower in plants exposed to 128 mmol L −1 H 2 O 2 compared with control plants, no significant differences were detected among treatments. Soaking roots in 16 mmol L −1 H 2 O 2 induced the highest rosmarinic acid (RA) content, and 16, 32, and 64 mmol L −1 H 2 O 2 significantly increased tilianin content in the whole plant compared with the control. The highest acacetin content was detected under 32 mmol L −1 H 2 O 2 . In addition, root extract of A. rugosa had the highest RA concentration, and the tilianin concentration was the highest in flowers. Collectively, these results show that soaking roots in 16 and 32 mmol L −1 H 2 O 2 at 3.5 weeks after transplanting promotes secondary metabolites of hydroponically grown A. rugosa.