Abstract
We investigated the effects of red and blue light on the growth and content of bioactive compounds of Salvia plebeia R. Br in a closed-type plant production system (CPPS). The seedlings of Salvia plebeia R. Br. were transplanted into a deep floating technique system with nutrient recycling (pH 6.5 and electrical conductivity (EC) 1.5 dS∙m−1). The plants were cultured for a duration of 35 days at 25 ± 1 °C, with relative humidity 60 ± 5%, a 12/12 h (light/dark) photoperiod, and a light intensity of 180 µmol∙m−2∙s−1 photosynthetic flux photon density, providing standard fluorescent (FL) lighting and various light qualities of red:blue ratios (10:0, 7:3, 5:5, 3:7, and 0:10) in the CPPS. The growth characteristics of Salvia plebeia R. Br., such as leaf length, leaf area, and fresh and dry weights of shoots, were the greatest in Red only and R7B3. The leaf shape index was the highest in Blue only and specific leaf weight was lower in FL and Blue than in the other treatments. The photosynthetic rate was the highest in R7B3. The total phenolic and flavonoid concentrations per gram of fresh weight of Salvia plebeia R. Br. were higher in combined light, such as R7B3, R5B5, and B3B7, than in the monochromatic light treatments. However, the antioxidant activity per fresh weight was the highest in FL. In conclusion, the results suggest that 7:3 is the most effective red and blue light ratio for production of high quality Salvia plebeia R. Br. in a CPPS.
Highlights
The absorbance of the supernatant was measured with a spectrophotometer (Libra S22, Biochrom Ltd., Cambridge, UK) at 735 nm to determine the total phenolic concentration, which is expressed as μg gallic acid equivalent (GAE) per mg of fresh weight (FW)
The absorbance of the samples was measured with a spectrophotometer at 415 nm to determine the total flavonoid concentration, which is expressed as μg quercetin equivalent (QE) per mg of FW
Several studies have reported that red light increased the fresh and dry weights of shoots in various crops, such as Solanum lycopersicum L. seedlings, fresh and dry weights of shoots in various crops, such as seedlings, Perilla frutescens L., lettuce, and Mesembryanthemum crystallinum L. [25,47,48,49]
Summary
Plant responses to red light generally include seed germination, cell development and elongation, fresh and dry weight increases, and increase in leaf area [23,24,25]. The plant response to blue light includes stomatal opening, compact growth, and flavonoid accumulation [26,27]. Reported that lettuce had a smaller leaf area and lower fresh weight when grown under monochromatic light compared with combined red and blue light. The objective of this study was to investigate the influence of red and blue light irradiation on the growth, photosynthetic rate, and bioactive compound accumulation for the cultivation of the medicinal plant, Salvia plebeia R.
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