Effect of Light Intensity and Light/Dark Period on Iridoids in Hedyotis diffusa

Abstract

The purpose of this study was to clarify the effects of light intensity and light/dark period on the concentration of iridoids in the plant Hedyotis diffusa, which finds use in herbal medicine. To investigate the effect of light conditions, plants were grown in a chamber with factorial treatments comprising three light/dark periods (14/10 h, 19/5 h and 24/0 h) and two light intensities (photosynthetic photon flux density of 142 and 40 μmol m⁻² s⁻¹). The epigeous dry weight was greatest with the treatments using high light intensity regardless of light period. The concentration of asperuloside (an iridoid) at 24/0 h was noticeably greater than that at 14/10 h or 19/5 h irrespective of light intensity. It was expected that the critical light period for the production of asperuloside would occur between 19 h and 24 h. The content of asperuloside was greatest at 24/0 h under high light intensity. Therefore, high light intensity and a 24/0-h light/dark period can produce high-quality H. diffusa.