There has been much interest in artemisinin owing to its excellent activity against malaria, an infectious
disease threatening the tropical world. However, the low artemisinin content (0.01–0.8%, DW) in
Artemisia annua, which is the only commercial source of artemisinin, makes artemisinin expensive to produce
and not yet available on a global scale. Here we show that foliar application of 100mgl−1 chitosan
improved artemisinin biosynthesis in A. annua. The content of dihydroartemisinic acid and artemisinin
in chitosan-treated leaves increased by 72% and 53% compared with control values, respectively. Chitosan
induced the expression of ADS and DBR2, which could explain the increase in level of artemisinic
metabolites. After chitosan treatment, the amounts of hydrogen peroxide (H2O2) and superoxide anion
(O2
−) in leaves of A. annua were 1.4 and 3.0 times higher than those of the control, respectively. Accumulation
of reactive oxygen species (ROS) probably accelerated the conversion of dihydroartemisinic
acid to artemisinin. Foliar application of 100mgl−1 chitosan had no harmful effect on A. annua growth.
The simple method described here could be an effective method to improve artemisinin production in A.
annua field cultivation.