OXIDATIVE PATHWAYS AND ESSENTIAL OIL BIOSYNTHESIS IN THE DEVELOPING CYMBOPOGON-FLEXUOSUS LEAF

The changes in essential oil content, in vivo capacity to incorporate [2-14C]acetate into essential oil and its constituents (citral and geraniol), geraniol dehydrogenase activity, and levels of some important reducing power generating enzymes were determined during Cymbopogon flexuosus (lemongrass) leaf development. Only young and rapidly expanding leaves were found to have the capacity to synthesize and accumulate essential oil and citral. The pattern of the ratio of the label incorporated in citral to that in geraniol, during leaf ontogeny, evinced parallelism with the geraniol dehydrogenase activity. The elevated levels of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NADP + -malic enzyme, and NADP + -isocitrate dehydrogenase coincided with the period of active essential oil biogenesis accompanying early leaf growth. The specific metabolic inhibitors (fluoride, borate, arsenate, and 2,4-dinitrophenol) of oxidative pathways considerably diminuted the incorporation of [2-14C]acetate into essential oil. The studies suggest active involvement of oxidative pathways in essential oil biosynthesis. Thus, there is tight integration of secondary metabolism with the primary metabolic pathways and with the developmental stage of the leaf