Growth and phytochemicals of ice plant (Mesembryanthemum crystallinum L.) as affected by various combined ratios of red and blue LEDs in a closed-type plant production system

Abstract

As a high value added crop, the ice plant (Mesembryanthemum crystallinum L.) as known to be effective in diabetes and is becoming widely used by consumers. This study aimed to improve the growth and phytochemical contents of the ice plant using combinations of red and blue light-emitting diodes (LEDs) in a closed-type plant production system. Seedlings of the ice plant were transplanted into a deep floating technique system with a recycling nutrient solution (EC 4.0 dS m-1, pH 6.5). The plants were cultured under a temperature 25 ± 1 ℃ and a relative humidity 60 ± 5%. The combinations of red and blue LEDs (R9B1, red:blue = 9:1; R7B3, red:blue = 7:3; R5B5, red:blue = 5:5; R3R7, red:blue = 3:7; and R1B9, red:blue = 1:9) were used at 150 ± 5 μmol·m-2·s-1 PPFD with a photoperiod of 14 h/10 h (light/dark) for 28 days. Growth of the ice plant presented significantly higher values under the R9B1 and R7B3 for high ratio of red LED treatments. The fresh and dry weights per plant of shoot were the lowest in the R1B9 at 4.49 g and 0.14 g, respectively. Total phenolic concentration, total flavonoid concentration, and antioxidant activity of the ice plant increased proportionally to the treated blue LED ratio. In addition, the concentration per dry weight of myo-inositol was the highest in the R1B9 at 310.83 mg g-1. While pinitol concentration of the ice plant showed no increasing tendency with blue LEDs, significantly higher values were obtained under the high blue ratios, such as R3B7 and R1B9 treatments. In conclusions, when considering the phytochemical contents per biomass of the ice plant consumed by actual consumers, it was the most effective applying red and blue LEDs in a closed-type plant production system at the 70-90% or 10-30%, respectively.