# Functions of Representative Terpenoids and Their Biosynthesis Mechanisms in Medicinal Plants
## 5 Accumulation Characteristics of Trepenoids and Their Transport  
The specific sites of terpenoid synthesis, storage, and utilization vary among medicinal plants. Multicellular glandular trichomes, which are outgrowths on the epidermal, possess the ability to secrete or store significant amounts of terpenoids. Glandular secretory trichomes, located on the surface of the leaves, are where artemisinin is synthesized and stored. Thus, the density of glandular trichomes affects artemisinin accumulation [71]. Cannabinoids are present in all _C. sativa_ aerial plants and the resin is the most highly concentrated. Cannabinoids were originally synthesized in the trichoid in the form of cannabic acid. Since acidic substances are highly toxic to plant cells, the final stage of their synthesis takes place outside the cells of the trichosomes [72]. The roots of _C. sativa_ also contain triterpenoids' active compounds [73].The high concentrations of monoterpenoids occur in capitate glandular trichomes in bracts; cannabinoids are also stored in the glandular trichome secretory cavity, but they are found predominantly in female flowers [24]. In _T. media_, taxol exhibits special mechanisms for synthesis and storage to prevent toxic effects on its source plant. Taxol can be isolated from nearly all its plant tissues, but its content is higher in the stems, primarily accumulating in the outer bark, compared to the roots and needles [74]. The present studies also reveal that taxol is stored in hydrophobic bodies within the wood parenchyma rays and phloem. This storage can help protect living cells from the cytotoxic effects of taxol [75]. By contrast, in _G. biloba_, the terpenoids are primarily extracted from the leaves. However, experiments using \({}^{14}\)CO\({}_{2}\) and (U-\({}^{14}\)C) glucose-labeled revealed that their biosynthesis site is not in the leaves but in the roots [76]. The content of terpenoids found within the cortex (bark) was 1.75 to 2.07 times higher than that found in the leaves. _GbLPS_, _GbIDS2_, _GbDXR2_, _GbDXS2_, and _GbGGPPS_, the core genes in the ginkgolide biosynthetic pathway, exhibited a high level of expression in roots, confirming that the roots are the main site of terpenoid biosynthesis [77; 78]. Metabolic profiling and gene expression analysis indicate that ginkgolides are biosynthesized in the root fibrous and main root periderm tissues, and subsequently transported to the leaves [78]. Similarly, several major bioactive compounds have been extracted from the roots of _S. miltiorhiza_, including cryptotanshinone and tanshinone IIA. The genes relevant to transhinone synthesis, particularly _SmKSL1_, _SmCPS1_, and 19 candidate _SmCPYS_, are all highly expressed in root periderm tissue [79; 80], confirming that tanshinone accumulation mainly occurs in the _S. milliorrhiza_ root phloem. Since some terpenoids are produced and stored at different sites in plants, it is necessary to study their transport [81]. However, the transport mechanisms of terpenoids have not been extensively researched in medicinal plants. ATP-binding cassette (ABC) transporters are present in most eukaryotic organisms, and can be categorized into eight subfamilies (ABCA to ABCH). They can drive the influx or efflux of secondary metabolites into cells [82; 83]. A few transporters from the ABCG subfamily are implicated in terpenoid transport. The pleiotropic drug resistance (PDR) transporters, belonging to the ABCG subfamily, were found to be responsible for the membrane transport of terpenoids in medicinal plants [84; 85]. In _P. ginseng_, _PgPDR3_ has been implicated in corresponding ginseng accumulation [85]. Similarly, in _A. annua_, _AaPDR3_ is involved in both the formation and transport of \(\beta\)-caryophyllene [86]. Additionally, the genome of _S. milliorrhiza_ contains a total of 114 genes that encode ABC transporters [83].