Response Of Physiology And Artemisinin Biosynthesis In Artemisia Annua L.under Salt Stress

Artemisinin, an endoperoxide sesquiterpene lactone produced by the traditional Chinese medicinal Artemisia annua L., is an effective drug against chloroquine-resistant strains of Plasmodium falciparum and in the treatment of cerebral malaria, with little toxicity to humans. The intact plant remains the main source of artemisinin production, but generally at low artemisinin content, limiting the large-scale production of artemisinin. In recent years, a number of studies found that many physical and chemical factors could induce the synthesis of secondary metabolites of medicinal plants, and had used them in the induction of artemisinin biosynthesis. Salinity is one of the major environment factors and many scientists concerned about its impact on plant growth. In recent years, scientists treated salt stress as a stimulating factor to induce accumulation of plant secondary metabolites. In the present study, we studied the effect of salinity on growth, physiology and the accumulation of secondary metabolites. The mechanism of induction has also been investigated.Firstly we investigated the growth of A. annua after salinity treatment. Significant reduction in growth per culture was observed with increasing salt concentration. The dry weight of shoots decreased by 76.92% after 8 g/L Na Cl treatment. In comparison to control, the stomatal density and photosynthetic pigments decreased in the treated plants at 4 g/L Na Cl,. The reduction of net photosynthetic rate, internal CO2 concentration, stomatal conductance(27.9%, 10.5% and 39.5% less than the control, respectively) were all observed under salt stress.Salinity caused the reactive oxygen burst and lipid peroxidation damage in the early stage. Na Cl treatment increased the content of O2-, H2O2 and MDA by 41.7%, 72.7% and 25.2% higher, respectively. The activitis of antioxidant enzymes were also significantly increased in salt-treated plants. G6 PDH activity under salt stress was also increased by 32.11%. After using 1 m M glucosamine(specific inhibitors of G6PDH), we found that G6 PDH activity can affect the generation of reactive oxygen species under salt stress.Salt stress can also affect the composition of the volatile oil components. Salinity induced the increase of artemisinin content, and also induced the density of glandular trichomes on leaves simultaneously. Trichome density was 62.5% and 66.7% higher on adaxial and abaxial leaf surfaces of salt-treated plants than that of control plants. The expression levels of key genes CYP71AV1 and ADS in artemisinin biosynthesis were significantly increased under salt stress. In addition, the results showed that the change of G6 PDH activity can affect the artemisinin content and the expression level of the artemisinin biosynthesis genes under salt stress.In summary, this study explored the physiological mechanism of salt stress inhibited the growth of A. annua, the role of G6 PDH in reactive oxygen burst under salinity and the mechanism of artemisinin accumulation from relative expression of genes of artemisinin biosynthesis. We first proposed that the increase of G6 PDH activity contributes to the artemisinin biosynthesis under salt stress. This work proposes an effective approach to use Na Cl solution as the elicitor to induce artemisinin biosynthesis and provides the reference basis to research the response mechanism of A. annua under salt stress.