Salicylic acid and methyl jasmonate but not Rose Bengal enhance artemisinin production through invoking burst of endogenous singlet oxygen

As a cis element responsive to oxidative stresses, the promoter of amorphadiene synthase gene (pADS) from Artemisia annua was also found to be inducible by salicylic acid (SA) and methyl jasmonate (MJ), which had been evident by phenotyping pADS-driven β-glucuronidase reporter gene (GUS) in transgenic Nicotiana tabacum incubated with SA/MJ. Furthermore, SA/MJ-treated A. annua exhibited a correlation of the up-regulation of ADS gene with the emission of singlet oxygen (1O2), suggesting that SA/MJ induced artemisinin overproduction through invoking 1O2 burst. Supplement with Rose Bengal (RB), a photosensitizing 1O2 generator, or direct exposure to a 1O2-generating pool, however, failed to facilitate artemisinin accumulation in subjected A. annua. Alteration of metabolite profiles and fluctuation of H2O2 level suggested that RB treatment might have led to a diminished endogenous 1O2 release from A. annua, thereby reiterating an important role of the endogenous 1O2 rather than the exogenous 1O2 in enhanced artemisinin production.