Sesamin is a major lignan constituent of sesame (Sesamum indicum) seed and considered responsible for
a number of beneficial human health effects. We previously reported that sesamin is present in sesame
leaves, and proposed use of sesame leaves as a sesamin-containing material. This study focused on the
possibility that both leaf yield and sesamin content would be increased with increasing photoperiod.
Additionally, it was hypothesized that sesamin content would be affected by photoperiod in relation to
CYP81Q1 gene expression. We thus investigated the effect of photoperiod on growth and leaf sesamin
content in relation to CYP81Q1 gene expression to confirm our hypothesis. Under short-day (SD) condition,
increase of leaf area was suppressed due to the phase transition from vegetative to reproductive
growth, which resulted in reduction of leaf yield. Under long-day (LD) conditions, vegetative growth
was continued, and both leaf area and yield increased as photoperiod increased up to 24 h (continuous
light). Sesamin accumulated particularly in the leaves of plants grown under a 24-h photoperiod for 4
weeks. High expression level of the CYP81Q1 gene in those plants indicates that photoperiod-dependent
differences in leaf sesamin content correlate with differences in CYP81Q1 gene expression levels. We conclude
that cultivation under continuous light enables high-yield production of sesame leaves containing
distinctively high levels of sesamin.