Optimizing the Electrical Conductivity of a Nutrient Solution for Plant Growth and Bioactive Compounds of Agastache rugosa in a Plant Factory

Abstract

The objective of this study was to determine the proper electrical conductivity (EC) of a nutrient solution (NS) for accumulating bioactive compounds of Agastache rugosa without decreasing plant growth. Six-week-old seedlings were transplanted in a deep flow technique system with Hoagland NS with a 2.0 dS·m−1 EC for the initial week. From eight days after transplanting, the plants were treated with six EC treatments of 0.5, 1.0, 2.0, 4.0, 6.0, and 8.0 dS·m−1 for three weeks. Plant growth parameters, leaf gas exchange parameters, the relative chlorophyll value, and the ratio of variable to maximum fluorescence (Fv/Fm) were measured, and the rosmarinic acid (RA), tilianin, and acacetin concentrations were analyzed at 28 days after transplanting. The results showed that almost all plant growth parameters were maximized at 2.0 and 4.0 dS·m−1 and minimized at 8.0 dS·m−1 compared with the other EC treatments. The relative chlorophyll and Fv/Fm values were maximized at 2.0 and 4.0 dS·m−1. Similarly, leaf gas exchange parameters were increased at 2.0 and 4.0 dS·m−1. The RA content exhibited significantly higher values at 0.5, 1.0, 2.0, and 4.0 dS·m−1 compared with other treatments. The tilianin and acacetin contents exhibited the significantly highest values at 4.0 and 0.5 dS·m−1, respectively. These results suggest optimal EC treatment at 4.0 dS·m−1 for increasing bioactive compounds in A. rugosa plants without decreasing plant growth. Excessively high or low EC induced salinity stress or nutrient deficiency, respectively. Furthermore, among the plant organs, the roots of A. rugosa contained the highest RA concentration and the flowers contained the highest tilianin and acacetin concentrations, which revealed a higher utilization potential of the roots and flowers for bioactive compounds.

The Effects of Root Temperature on Growth, Physiology, and Accumulation of Bioactive Compounds of Agastache rugosa

“…Hoagland nutrient solution was used to irrigate for seedlings. Electrical conductivity (EC) and pH values were adjusted to 1.2 dS•m −1 and 6.0 [18].…”

“…The dried powder (0.1 g) of each plant organ was blended with 80% (v/v) MeOH (1.5 mL) and then sonicated for 60 min. The solution was centrifuged at 12,000× g for 10 min using a microcentrifuge (R17 Plus, Hanil Scientific Co., Ltd., Gimpo, Korea) at 4 • C. The rosmarinic acid (RA), tilianin, and acacetin concentrations were determined by a HPLC system (1260 Infinity, Agilent Technologies, Santa Clara, CA, USA) [3,18]. The supernatant was filtered through a filter (0.45 µm), and then a high-performance liquid chromatography (HPLC) analysis was conducted with a C18 column (250 mm × 4.6 mm, 5 µm; RS tech, Daejeon, Korea) at 30 • C. Standard compounds of pure RA, tilianin, acacetin, HPLC grade acetic acid, methanol, the pure compounds, analytical grade solvents, and reagents from Sigma-Aldrich, Co., Ltd., (Seoul, Korea) were used in this experiment.…”

Optimization of Indole-3-Acetic Acid Concentration in a Nutrient Solution for Increasing Bioactive Compound Accumulation and Production of Agastache rugosa in a Plant Factory

“…Food production with high quality and productivity can be achieved by growing in a plant factory, which is one way to satisfy very specific requirements for plant growth and secondary metabolite accumulation [14]. Various external factors such as the light, temperature, electrical conductivity, root temperature, and hormones affect the accumulation of bioactive compounds in A. rugosa [15][16][17][18]. Furthermore, plant hormones such as indole-3-butyric acid (IBA), 1-naphtha-leneacetic acid (NAA), indole-3-acetic acid (IAA), and phenylacetic acid (PAA) play an essential role not only in the growth but also in the accumulation of antioxidant enzymes and bioactive compounds in plants [19,20].…”

Phenotyping of Different Italian Durum Wheat Varieties in Early Growth Stage With the Addition of Pure or Digestate-Activated Biochars

“…The much higher EC, indicating a higher concentration of dissolved ions and salts, exhibited by the digestate-treated biochar samples (B1D and B2D), both at T 0 and T f , is also an indication of a greater amount of available mineral elements with respect to the treatments with pure biochar (B1 and B2). It is not uncommon to find that high EC has detrimental effects on plants, affecting their equilibrate growth particularly in the early growth stage ( Lam et al, 2020 ; Celletti et al, 2021 ).…”