Impacts of Different Light Spectra on CBD, CBDA and Terpene Concentrations in Relation to the Flower Positions of Different _Cannabis Sativa_ [PERSON]. [PERSON]  
[PERSON]  
1 Agnonomy, Institute of Crop Science, University of Hohenheim, 70599 Stuttgart, Germany 1  
[PERSON]  
1 Agnonomy, Institute of Crop Science, University of Hohenheim, 70599 Stuttgart, Germany 1  
[PERSON]  
2 Biostatistics, Institute of Crop Science, University of Hohenheim, 70599 Stuttgart, Germany 2  
[PERSON]  
3 Department of Agricultural Sciences, Viikki Plant Science Centre, University of Helsinki, P.O. Box 27, FI-00014 Helsinki, Finland 3  
[PERSON]  
1 Agnonomy, Institute of Crop Science, University of Hohenheim, 70599 Stuttgart, Germany 1  
Footnote 1: email: p.bobo.bo. pathway (MEP). PKS produces olivetolic acid (OLA) [10], which is the starting compound for cannabinoid synthesis. Two synthesis pathways are responsible for terpen: the MVA [11] or MEV [12] pathway and the MEP pathway [13], each of which has dimethylallyl diphosphate (DMAPP) as the end product [14]. In the MEV/MVA pathway, DMAPP is further condensed to farnesyl pyrophosphate (FPP), which forms the precursor for sesquiterpenes [15]. On the other hand, MEP synthesizes geranyl diphosphate (GPP) from DMAPP and is responsible for the formation of monoterpenes. Additionally, GPP together with OLA forms the precursor of all cannabinoids, cannabigerolic acid (CBGA) [16]. Hence, GPP is the connection between monoterpene and cannabinoid biosynthesis. Each pathway is determined by key enzyme steps. During cannabinoid synthesis, tetraketide synthase (TKS) plays an important role, followed by olivetolic acid cyclase (OAC) [17]. Of central importance is geranyl pyrophosphate:olivetolate geranyltransferase (PT4) for the formation of CBGA. Terpene biosynthesis involves distinct enzyme sequences for the formation of mono- and sesquiterpenes. For monoterpenes, 1-deoxy-D-xylulose 5-phosphate synthase (DXS) and 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) are crucial, initial enzymes. Hydroxyethylglutaryl-CoA synthase (HMGS) followed by hydroxymethylglutaryl-CoA reductase (HMGR), in contrast, are involved in the formation of sesquiterpenes [18] (Figure 1). Every setting in the cultivation system of _Cannabis sativa_ L. is accompanied by the up- and down-regulation of enzyme expressions, which leads to increase or decrease in the respective end products. Research on the influence of the enzyme steps in cannabinoid biosynthesis is still in its infancy. For terpen biosynthesis, however, knowledge can be derived from other plant species. Major influences are light, temperature and abiotic and biotic stresses, which affect the flow direction of isopenoid precursors between the MEP and MEV/MVA pathways [18], through modulating enzyme expression. Increasing light intensity leads to a decrease in the MEV/MVA pathway, whereas abiotic and biotic stresses can enhance it [19; 20; 21]. By contrast, the MEP pathway is promoted by light intensity and temperature [22; 23] (Figure 1). Figure 1: Simplified Cannabis and Terpene Biosynthesis based on [1; 3; 11; 24; 25]. Pathways are outlined in red, and important enzymes are highlighted in red. CBCA: Cannabichromenic acid; CBC: Cannabichromene; \(\Delta^{9}\)-THCA: \(\Delta^{9}\)-Tetrahydrocannabinolic acid; \(\Delta^{9}\)-THC: \(\Delta^{9}\)-Tetrahydrocannabinol; CBN: Cannabinol; CBDA: Cannabidiolic acid; CBD: Cannabidiol. For the final conversion into the respective mono- and sesquiterpenes, terpene syntheses (TPSs) [25; 26; 27] are responsible, which can be classified into different clustering gene groups [3; 4] and may be light-mediated [28]. According to [4], TPS-a (caryophyllene and humulene), TPS-g (linalool and nerolidol) and TPS-b (\(\beta\)-Myrcene, limonene, \(\alpha\)-pinene and monoterenes in general) are responsible for the respective terpene syntheses. Despite the progress in deciphering the genetic principles of TPSs, actual terpene profiles are still difficult to predict [3].