Chemical and morphological studies of the effects of ageing on monoterpene composition in Mentha ×piperita leaves

Abstract

The effects of ageing on monoterpene composition in Mentha ×piperita have been studied by analyses of microsamples obtained by coupling a desorption–concentration–introduction technique with a gas chromatograph. The appearance and the development of the two types of glands of shoot meristem studied by scanning electron microscopy show that the capitate glands appear before the peltate glands. The chromatographic analyses of meristem and different primordial leaf pairs show that the monoterpenes are only detected if the leaf bears peltate glands and that the first cyclic compound accumulated is limonene. The biochemical variations of the reduction of menthone to menthol in the midstem leaves and of acetylation of menthol in the basal leaves start at the distal extremity of the leaf and progressively move towards the base. The maturation of the plant followed by the shift of the level of leaf in which menthone and menthol are present with the same percentage as a function of time is a linear phenomenon. Key words: peppermint, trichomes, monoterpenes, biochemical variations, ageing.