Effects of daylength on the monoterpene composition of leaves of Mentha x piperita

The monoterpene composition of leaves of Mentha x piperita has been studied by direct analyses of samples (Desorption-Concentration-Introduction Technique). Kinetic studies on individual pairs of leaves from plants subjected to different photoperiodic treatments (long or short photoperiod followed or not by an inversion of the initial photoperiod) show that the photoperiod received by the young leaves directly influenced the oil composition. Therefore the photoperiod as such is responsible for the variations of the monoterpene metabolic pathway. This conclusion is based on the likelihood that the reducing pathway (menthone-menthol) was developed in young leaves on condition that they are subjected to a long photoperiodic treatment and that the metabolic pathway originally induced by the daylength in the oldest leaves was not changed by the inversion of the initial photoperiodic treatment.