Objective:To explore the effect of gibberellic acid (GA3) and its inhibitor paclobutrazol (PBZ)on chemical composition and their pharmacological effects on Andrographis paniculata (Burm.f.) Wall.ex Nees,and to clarify action mode of andrographolide.Methods:The chemical composition was extracted by sequential extraction with hexane,dichloromethane,ethyl acetate and methanol,respectively.Andrographolide and its derivatives were evaluated by HPLC.Moreover,the metabolic profiling was analyzed by GC-MS.Inhibitory effect of crude extracts was tested against Staphylococcus aureus using agar well diffusion method.Mode of action was tested against mutant yeast by spotting assay.Andrographolide were tested for their mode of action against eukaryotes.Results:Among different solvents,dichloromethane gave the highest yield of crude (3.58％ DW),with the highest andrographolide content (8.3 mg/g DW).The effect of plant hormone (10 mg/L GA3 or PBZ) on phytochemical variations and bioactivity of Andrographis paniculata was demonstrated.It was found that PBZ promoted sesquiterpene compounds about 3.5 times over than GA3 treatment.But inhibitory effect of extracts against Staphylococcus aureus was highest in GA3 treated plants;andrographolide and 14-deoxy-11,12-didehydroandrographolide contents were significantly higher than those of water or PBZ.It was found that there were 11 strains involving in ergosterol biosynthesis,V-ATPase activity and homeostasis,and superoxide detoxification process.In this regard,andrographollde might cause the damage on the lipid bilayer of yeast cell and plasma membrane by interfering ergosterol biosynthesis.Conclusions:It is found that GA3 promotes andrographolide and 14-deoxy-11,12-didehydroandrographolide content while PBZ promotes sesquiterpene content.Andrographolide might cause the damage on the lipid bilayer of yeast cell and plasma membrane by interfering ergosterol biosynthesis.It might also affect mitochondria electron transport chain,leading to the occurrence of ROS,which can further harm cell organelles.However,the library screening is the first step to investigate mode of action of andrographolide.