In Vitro Photomorphogenesis, Plant Growth Regulators, Melatonin Content, and DNA Methylation under Various Wavelengths of Light in Phalaenopsis Amabilis

We tested the feasibility to promote growth and shoot proliferation of Phalaenopsis through different wavelengths of LED and fluorescent. Therefore, shoot proliferation and photomorphogenesis responses to light quality were measured at the level of endogenous plant growth regulators including indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), trans-Zeatin (ZEA), and Kinetin (KIN), abscisic acid (ABA), gibberellic acid (GA3), melatonin (MEL), and DNA methylation patterns. It was found that shoot proliferation occurred better under the irradiation of blue + green. Besides, biomass (fresh and dry weight) was higher under white LEDs, which was not significantly different from fluorescent and blue + red. The ZEA content was higher in fluorescent, white, and red and the KIN content was higher in fluorescent and blue + green treatments. The sum of both cytokinins under fluorescent and red was higher without significant differences with white and blue + green. The content of IAA and IBA was higher under red + blue and red light without significant differences with green, blue + green, and fluorescent. The lowest content of cytokines was detected under blue, green, and red + green and the lowest content of auxins was red + green and blue wavelengths. The ratio of auxins to cytokines was the highest under green and red + blue and the lowest under fluorescent, white and red-green. ABA was not significantly affected. Red + blue and green + blue light increased the GA3, while fluorescent, white, red + green, and blue decreased. MEL content was higher in blue and red and was lower in red + green. The highest percentage of unmethylated sites was found under fluorescent (25.76%) and red + blue (25.76%) followed by white LEDs (24.24%). The lowest percentage of unmethylated sites was observed under red + green (18.18%) and blue + green (18.18%). The best branching performance was associated with higher kinetin content, total cytokinins, and GA3 under blue + green. However, after branching, the transfer of samples to the full spectrum is recommended to improve the biomass and normal growth. Red + blue and blue + green increased shoot induction. Normal growth were observed under the full-spectrum lighting. Mono- and dichromatic (except Red + blue) LEDs enhanced DNA methylation compared to full-spectrum lighting.