Effect of photoperiod on growth of the plants, and sesamin content and CYP81Q1 gene expression in the leaves of sesame (Sesamum indicum L.)

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.