Investigation of MEP 2CMethy1DErythritol4Phosphate Pathway of Essential Oil Biosynthesis in Lemongrass Cymbopogon flexuosus Steud

Abstract

Cymbopogon flexuosus (Steud) cv. Suvarna provides lemon scented essential oil of wide industrial applications in flavor, fragrance, perfumery, pharmaceuticals and food industries. The present thesis has centered on the investigation of the developmentally regulated accumulation and biosynthesis of essential oil in C. flexuosus cv. Suvarna using 13C-glucose stable isotope labeling techniques combined with quantitative NMR spectroscopy. The thesis also deals with isolation, purification and characterization of the DXS and DXR key enzymes of the MEP pathway. For the first time in present thesis fosmidomycin and mevinolin the specific metabolic inhibitors were used to investigate the roles of the acetate-MVA and MEP pathway in essential oil biosynthesis. One of the aims of this thesis was to isolates and identify GES activity and its role in the biosynthesis of citral. A scheme for biosynthesis of citral has been proposed as MEP IPP GPP Geraniol Citral. Essential oil of C. flexuosus cv. Suvarna consists of at least 20 different monoterpenes with citral as the major monoterpene which accounted for 70-80% of total monoterpenes. The young and rapidly expanding (10-20 d) leaves were found biogenetically most active in accumulation and biogenesis of essential oil. Essential oil content and compositions markedly fluctuates accompanying leaf development, with leaf positions and leaf age. The levels of geranyl acetate and geraniol together declined with a corresponding increase in citral (geranial + neral) percentage. Results of experiment using [1-13C]-glucose in combination of quantitative NMR spectroscopy suggested that biosynthesis of citral proceeds via the MEP pathway. Incorporation of 13C glucose in citral in the presence of mevinolin and fosmidomycin has also favored the MEP pathway origin of the citral. The activities of DXS and DXR enzymes were highest during very early stage of leaf growth which can be attributed to the maximum synthesis and accumulation of essential oil.