# Lemongrass Essential Oil Components with Antimicrobial and Anticancer Activities
## 2 LEO: Biosynthesis and Chemical Composition  
Lemongrass (_Cymbopogon_ spp.) oil is a cocktail of various terpen and terpenoids, out of which the major components belong to cyclic and acyclic monoterenes. The monoterenes are derived from geranyl diphosphate (GPP). The GPP is a fusion component of isopentenyl diphosphate (IPP) and its allylic isomer dimethylallyl diphosphate (DMAPP) (Figure 2). The IPP is a precursor of all the terpen and terpenoids. Earlier it was widely accepted that plants produce IPP through a cytoplasmic mevalonate (MVA) pathway. How  
Figure 1: Morphological and anatomical profile of lemongrass (_Cymbopogon flexusus_ (Steud.) [PERSON]) plants. The morphological representation of 150-days-old healthy lemongrass plants. Scanning electron microscopy (SEM) analysis of lemongrass leaf visualizing trichomes at \(\times\)500 magnification, stomatal characteristics at \(\times\)1500 magnification and Images provided by [PERSON]’s laboratory. ever, empirical studies reveal that a newly discovered methylerythnitol phosphate (MEP) pathway for monoterenes biosynthesis is more dominant in lemongrass species [11]. The plasidic MEP pathway begins with the reaction of pyruvate with thiamine diphosphate (TPP), which yields hydroxyethyl-TPP. Hydroxyethyl-TPP, upon reacting with glyceraldehyde 3-phosphate (GAP), releases 1-deoxy-D-xylulose 5-phosphate (DXP). Subsequently, DXP rearranges and reduces to MEP, which is further phosphorylated and ultimately generates IPP. On the other hand, the MVA pathway involves the condensation of three acetyl-CoA molecules into 3-hydroxymethylglutaryl-CoA (HMG-CoA). The HMG-CoA is reduced to MVA and the subsequent steps of MVA phosphorylation produce IPP. The IPP produced from the MEP/MVA pathway reacts with DMAPP to yield GPP, which subsequently forms geraniol in lemongrass. Geraniol, through different reversible reactions, produces all the major components of lemongrass oil [12] (Figure 2). Figure 2: A mechanistic model for the biosynthesis of lemongrass essential oil and its crosstalk with other metabolic processes. Different cellular organelles work in tandem for oil production in lemongrass leaves. The lemongrass chloroplast, like most of the other plants, produces glucose through photosynthesis. The glucose undergoes glycolysis in the cytoplasm and yields pyruvate, a two-carbon compound. Lemongrass uses pyruvate as a substrate for the biosynthesis of isopentenyl diphosphate (IPP) units, either through the cytoplasmic mevalonate (MVA) pathway or plasidic methylerythnitol phosphate (MEP) pathway in their young and rapidly growing leaves. Alternatively, mitochondria can import pyruvate and yield citrate through the tricarboxylic acid (TCA) cycle. The citrate can transform into Acetyl-CoA and join the MVA pathway to yield IPP units. The IPP produced through both pathways is converted into geraniol mediated by geranyl diphosphate (GPP) in lemongrass plastids. The geraniol is considered as a precursor for essential oil biosynthesis in lemongrass and yields all the major components through multiple reversible and irreversible reactions. The plasidic bubble highlights these reactions along with their substrates. DMAPP, dimethylallyl diphosphate; DXP, 1-deoxy-D-xylulose-5-phosphate; MEP, 2-C methylerythnitol 4-phosphate; CDP-ME, 4-diphosphocytidyl-2-C-methyl-D-erythnitol; CDP-MEP, 4-diphosphocytidyl-2-C-methyl-D-erythnitol-2-phosphate; MECPP, 2-C-methyl-D-erythnitol 2,4-cyclodiphosphate. The image is drawn by the authors on the basis of teaching texts for plant biochemical pathways for secondary metabolites. LEO is produced only in young and rapidly growing lemongrass leaves and floral tops and is stored in specialized parenchymal oil cells between vascular bundles proximal to non-photosynthetic tissue [13]. The amount of lemongrass oil is about 1-2% of the plant's total dry weight [14]. However, various drying methods can produce different content and quality of LEO [15].