Abstract
The aim of this study was to clarify how the air temperatures during the light and dark periods affect growth and biosynthesis of the iridoid glycoside asperuloside in Hedyotis diffusa. Ten experimental air temperature treatments were established in a growth chamber during the cultivation period: (light/dark period air temperature) 30/15°C, 20/20°C, 25/20°C, 30/20°C, 35/20°C, 25/25°C, 30/25°C, 35/25°C, 40/25°C and 30/30°C. It was found that the stem length and epigeous dry weight were greatest with the 35/25°C treatment, whereas the leaves near the apical buds of the branches became blackened with the 40/25°C treatment, indicating that 35°C represents the upper air temperature limit during the light period for growth without any physiological disorder. By contrast, the asperuloside concentration was high with an air temperature of 25°C or less during the light period and 20°C or less during the dark period, and was greatest with the 25/20°C and 30/20°C treatments. Thus, air temperatures of 25–30°C during the light period and 20°C during the dark period are effective for maximising the asperuloside content in H. diffusa.
