These secondary metabolite levels g

These secondary metabolite levels generally tend to increase with increasing photoperiod, unless the plant growth is inhibited. Interestingly,
Hirai et al. (1993, 1995) reported that accumulation of
phenylpropanoids including a lignan, pinoresinol-O-ˇ-d-glucoside
in the cotyledons of Japanese morning glory (Pharbitis nil), as a
result of increased activity of phenylalanine ammonia-lyase (PAL),
did not occur under an 8-h photoperiod, but occurred under a 24-
h photoperiod.