Red:Blue LED light proportion affects biomass accumulation and polyamine metabolism in Anoectochilus roxburghii studied by nano-electrospray ionization mass spectrometry

Light quality affects the plant growth, physiology, and polyamine (PA) metabolism. Anoectochilus roxburghii is an ornamental, medicinal, and culinary perennial herb in many countries. In this study, we identified the optimal light environment for enhancing the growth of A. roxburghii in vitro, and analyzed PA metabolism under blue (B), three red:blue combinations at different proportions of the total incident photon flux density (R1B2: the ratio of 1: 2, R1B1: the ratio of 1: 1, and R2B1: the ratio of 2: 1, respectively), red (R), and white light (W) environment for 120 days. The biomass accumulation and stomata characteristics were evaluated, as well as total phenolic, total flavonoids, soluble sugars, and soluble proteins. Besides, nine PA compounds were quantitatively analyzed by nano-electrospray ionization mass spectrometry (nano-ESI-MS) without complex sample pretreatment. The results showed that the biomass, total phenolic, total flavonoids, soluble sugars, and soluble proteins were significantly higher in the R1B1 group, which was more conducive to stomata opening. The accumulation of the nine PA compounds increased significantly in the B and R groups, compared with W group, but decreased in the combinations of red and blue lights, especially in the R1B1 group, which A. roxburghii showed better growth. We conclude that the R1B1 could be used as the optimal growth light environment of A. roxburghii tissue culture. Nano-ESI-MS could be used as a rapid and sensitive method to quantify PAs, providing new data for enhancing our understanding about the functions of PAs in plant-light environment interactions.