Fig. 3

Rhythmic changes in melatonin concentrations in H. perforatum L. leaves with time under 18-h light:6-h dark photoperiodic cycles (Zeitgeber time, ZT; solid diamonds) and constant light conditions (circadian time, CT; solid squares). The white bar at the top indicates the light period. The black-shaded bar at the top indicates the dark period and the subjective night. Data are the mean of three replicates