Site of Monoterpene Biosynthesis in Majorana hortensis Leaves

Excised epidermis of Majorana hortensis Moench (sweet marjoram) leaves incorporates label from U-¹⁴C]sucrose into monoterpenes as efficiently as do leaf discs, while mesophyll tissue has only a very limited capacity to synthesize monoterpenes from exogenous sucrose. These results strongly suggest that epidermal cells, presumably the epidermal oil glands, are the primary site of monoterpene biosynthesis in marjoram. Using a leaf disc assay, it was demonstrated that label from U-¹⁴C]sucrose is incorporated into monoterpenes most efficiently in very young leaves.