10The sesquiterpene phytolactone derived from Artemisia annua, artemisinin is 11 associated with a variety of novel biological properties, such as immunoregulatory and 12 anticancer effects, and therapeutic applications, apart from its main function as an 13 4 57 Naturally, artemisinin biosynthesis occurs in glandular secretory trichomes that are 58 present on foliage, stems and inflorescences of the A. annua plant [15, 16]. Due to its 59 compartmentalized synthesis and influence by physiological, seasonal and environmental 60 factors, artemisinin concentration is highly variable with reported values of 0.1 -10 mg g -1 61 dry weight (DW) [11, 17]. With the biosynthetic pathway of artemisinin formation fully 62 elucidated over the past decade, it was learnt that within the species A. annua two contrasting 63 chemotypes can be distinguished, which are characterized by the differing contents of 64 artemisinin and its precursor (Fig 1). While both possess artemisinin, the high-artemisinin 65 producing (HAP) chemotype contains relatively higher levels of dihydroartemisinic acid 66 (DHAA) and artemisinin, and the low-artemisinin producing (LAP) chemotype has higher 67 contents of artemisinic acid and arteannuin B (a non-antimalarial product) [18, 19]. Despite 68 the difference in biochemical phenotype which is attributed to the differential expression of 69 one artemisinin biosynthesis specific gene artemisinic aldehyde Δ11(13) reductase (DBR2), 70 both chemotypes undergo similar spontaneous photooxidation reactions to produce 71 artemisinin or arteannuin B from its direct precursors [20-23]. 72 Fig 1. Schematic representation of artemisinin biosynthesis. 73 Synthesis occurs in the glandular trichome secretory cells of A. annua and sequestration of 74 artemisinin takes place in the subcuticular space. The two branching pathways leading to 75 artemisinin and arteannuin B of the artemisinin biosynthetic pathway (dashed line box) are 76 depicted and the final non-enzymatic photo-oxidation reaction is shown in red. MEP, 77 methylerythritol 4-phosphate; MVA, mevalonate; GST, glandular secretory trichome; ADS, 78 amorpha-4,11-diene synthase; CYP71AV1, cytochrome P450 monooxygenase; DBR2, 79 artemisinic aldehyde Δ11(13) reductase; ALDH1, aldehyde dehydrogenase 1. 80 As a secondary metabolite used mainly in defence mechanisms, production of 81 artemisinin would naturally be induced and enhanced under environmental stresses. Under 5 82 such adverse conditions the elevation of secondary oxidative stress, which is a consequence 83 of primary biotic/abiotic stress, is in a direct synergistic relationship with artemisinin 84 production [24-27]. On such basis, the biotechnological method elicitation which mimics the 85 natural induction of plant stress is the method of choice to enhance the production of 86 artemisinin. The positive effects of UV-B and DMSO on the production of artemisinin had 87 been verified by previous studies on A. annua seedlings [28, 29], in vitro propagated plantlets 88 [30] and shoot cultures [31]. Former st...

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Artemisinin is a sesquiterpene lactone derived from Artemisia annua L., and has a variety of biological properties, such as immunoregulatory and anticancer effects, and therapeutic applications. As a result of its naturally low production and compartmentalised synthesis, the irregular agricultural supply often leads to price fluctuations and reduction of the artemisinin inventory. In this study, elicitation efficiencies of ultraviolet B (UV-B) and dimethyl sulfoxide (DMSO) on a low-artemisinin producing (LAP) chemotype of the species A. annua were investigated. Exposure of cell suspension cultures to short-term UV-B radiation and DMSO treatment did not result in significant changes in artemisinin yield. The lack of stimulation could be associated with the growth condition such as the incubation duration after treatment, the physiological state of suspension-cultured cells, and the regulation of cellular metabolic homeostasis. Further molecular analysis with RT-PCR revealed the absence of mRNA transcripts of key genes ADS, DBR2, and ALDH1 which might affect artemisinin synthesis. This study demonstrated the complexity of stress-induced responses of   cell suspension cultures in relation to metabolic processes which are important for artemisinin formation.