ONTOGENIC VARIATION OF THE ESSENTIAL LEAF OIL OF MELISSA-OFFICINALIS-L

Leaf verticils of a single plant of Melissa officinalis L., Lamiaceae, have been analyzed separately with regard to essential oil compositio n and content, Drastic changes in quantitative composition were observ ed between the leaf oil of the basal region and that from the top leav es. Particularly this holds true for the monoterpene aldehydes citrone llal and citral, the monoterpene esters methylcitronellate and geranyl acetate and the amount of sesquiterpenes. By analyzing individually ma pped glands from leaf tips of a defined age it could be demonstrated t hat the oil composition of corresponding glands changes dramatically e .g. from 0% to 71% citronellal within two months. Related to leaf weig ht and area, the essential oil yield was maximal in the small leaves o f the terminal verticils. The highest absolute amount of essential oil , however, was found in the largest leaves from the middle region of t he stem. The results are discussed with respect to the physiology of e ssential oil formation and turnover. Considering quality criteria for the leaf drug growing conditions and harvest time are suggested.