Exogenous GA3 and flowering induce the conversion of artemisinic acid to artemisinin in Artemisia annua plants

The contents of artemisinin and artemisinic acid were monitored in the Artemisia annua plants treated with GA3 at vegetative and flowering initiation stages. The highest artemisinin content was observed at full bloom. The decrease in artemisinic acid content occurred during the transition from the vegetative stage to the beginning of flowering. Endogenous GA3 content in the leaves peaked at full bloom. At the vegetative stage, in plants treated with various concentrations of GA3 , the content of artemisinin increased while that of artemisinic acid decreased. Apparently, the rate-limiting step in artemisinin biosynthesis was from artemisinic acid to artemisinin. The “bottleneck” of artemisinin biosynthesis was probably unlocked during the flowering or in the vegetative plants treated with GA3 , which triggered off the conversion of artemisinic acid to artemisinin.