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Different steps of monoterpene metabolism—disappearance of limonene, accumulation of 1,8-cineole, reduction of menthone to menthol and acetylation of menthol—have been studied in different parts of Mentha × piperita leaves of different ages. The analyses of different samples (leaf strips, disks and individual peltate trichomes, translucent or containing crystals from either epidermis) show that all these dynamic changes start at the distal extremity of the leaf and shift progressively towards the base. Except for the peltate trichomes localized within the leaf area, in which a metabolic step is being realized, the trichomes of other parts present a homogeneous monoterpene composition. The measurements of amounts of chlorophyll in two parts, distal and basal, of youngest leaves of terminal buds show that chlorophyll biosynthesis starts also at the distal extremity of the leaf. The regulation of the menthone reduction is discussed. |
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