Effects of R/B Ratio and Light Intensity of the LED Lamp on the Growth and Iridoid Glycoside Content of Hedyotis diffusa

Abstract

　This study aimed to clarify the effect of the photosynthetic photon flux density (PPFD) ratio of red light (R) on that of blue light (B) radiated from an light emitting diode (LED) source on the growth and asperuloside biosynthesis of Hedyotis diffusa. Five experimental treatments with different ratios were established in a growth chamber as follows: R0B100, R25B75, R50B50, R75B25 and R100B0. For each ratio, two levels of PPFD were used: 100 and 150 μmol m^-2 s^-1. The results revealed that, under the same PPFD, the epigeous dry weight increased with the red-light percentage under simultaneous red and blue irradiation and decreased under red or blue monochromatic light. Under a chosen ratio, the epigeous dry weight increased with the light intensity. Asperuloside biosynthesis was suppressed under monochromatic light conditions and enhanced under simultaneous ones due to the enhanced supply of glucose, the main substrate of asperuloside biosynthesis, regardless of the ratio. Therefore, we concluded that the epigeous dry weight determined the asperuloside concentration.