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Pulsed Electric Field (PEF) Treatment Results in Growth Promotion, Main Flavonoids Extraction, and Phytochemical Profile Modulation of Scutellaria baicalensis Georgi Roots
This study aims to explore the effect of pulsed electric field (PEF) treatment as a method very likely to result in reversible electroporation of Scutellaria baicalensis Georgi underground organs, resulting in increased mass transfer and secondary metabolites leakage. PEF treatment with previously established empirically tailored parameters [E = 0.3 kV/cm (U = 3 kV, d = 10 cm), t = 50 µs, N = 33 f = 1 Hz] was applied 1–3 times to S. baicalensis roots submerged in four different Natural Deep Eutectic Solvents (NADES) media (1—choline chloride/xylose (1:2) + 30% water, 2—choline chloride/glucose (1:2) + 30% water, 3—choline chloride/ethylene glycol (1:2), and 4—tap water (EC = 0.7 mS/cm). Confocal microscopy was utilized to visualize the impact of PEF treatment on the root cells in situ. As a result of plant cell membrane permeabilization, an extract containing major active metabolites was successfully acquired in most media, achieving the best results using medium 1 and repeating the PEF treatment twice (baicalein <LOQ, baicalin 12.85 µg/mL, wogonin 2.15 µg/mL, and wogonoside 3.01 µg/mL). Wogonin concentration in NADES media was on par with the control (plants harvested on the day of the experiment, ultrasound-mediated methanolic extraction, Cwogonin = 2.15 µg/mL). After successful extraction, PEF treatment allowed the plants to continue growing, with the lowest survival rate across treated groups being 60%. Additionally, an enhancement in plant growth parameters (length and fresh mass of the roots) and significant changes in the S. baicalensis root phytochemical profile were also observed.
Changes in Growth and Metabolic Profile of Scutellaria baicalensis Georgi in Response to Sodium Chloride
Scutellaria baicalensis Georgi is a valuable medicinal plant of the Lamiaceae family. Its roots have been used in Traditional Chinese Medicine (under the name Huang-qin) since antiquity and are nowadays included in Chinese and European Pharmacopoeias. It is abundant in bioactive compounds which constitute up to 20% of dried root mass. These substances are lipophilic flavones with unsubstituted B-ring, baicalein, and wogonin and their respective glucuronides–baicalin and wogonoside being the most abundant. The content of these compounds is variable and the environmental factors causing this remain partially unknown. The role of these compounds in stress response is still being investigated and in our efforts to measure the effect of NaCl treatment on S. baicalensis growth and metabolic profile, we hope to contribute to this research. Short-term exposure to salt stress (50, 100, and 150 mM NaCl) resulted in a marked increase of baicalein from 1.55 mg to 2.55 mg/g DM (1.6-fold), baicalin from 8.2 mg to 14.7 mg (1.8-fold), wogonin from 4.9 to 6.8 (1.4-fold), and wogonoside from 3.3 to 6.8 mg/g DM (2-fold) in the roots. Conversely, in the aerial parts, the content of individual major flavonoids: carthamidine-7-O-glucuronide and scutellarein-7-O-glucuronide decreased the most by 10–50% from 18.6 mg to 11.3 mg/g (1.6-fold less) and from 6.5 mg to 3.4 mg/g DM (0.52-fold less), respectively. The amino acid profile was also altered with an increase in root concentrations of the following amino acids: arginine from 0.19 to 0.33 mg/g (1.7-fold), glutamate from 0.09 to 0.16 mg/g DM (1.6-fold), alanine from 0.009 to 0.06 mg/g (6.8-fold), proline from 0.011 to 0.029 (2.4-fold) and lysine from 0.016 to 0.063 mg/g (3.9-fold). Aspartate concentration decreased from 0.01 to 0.002 mg/g (4.8-fold less) at 150 mM NaCl. In the aerial parts, the concentration and variation in levels of specific amino acids differed among groups. For instance, the glutamate content exhibited a significant increase exclusively in the treatment group, rising from 0.031 to 0.034 mg/g, representing a 1.2-fold increase. Proline concentration showed a marked increase across all treated groups with the highest from 0.011 to 0.11 mg/g (10-fold). In conclusion, moderate salt stress was shown to increase S. baicalensis root biomass and flavonoid content which is rarely observed in a glycophyte species and provides a foundation for further studies on the mechanisms of osmotic stress adaptation on the specialized metabolism level.