Abstract: We investigated the allelopathy mechanism of the diterpenoid oridonin to Arabidopsis thaliana. The germination rate, seedling growth, electrolyte leakage (EL), malondialdehyde (MDA), and three phospholipase activities (PLA₁, PLA₂ and PLC) of four Arabidopsis thaliana lines (the Colombia ecotype WT, and three phospholipase deletion mutants pla₁, pla₂and plc₁) were measured under different oridonin concentrations (10 and 60 μmol·L^-1). The results showed that germination was inhibited by oridonin, and PLA₁ and PLA₂ participated in this process. The growth of root and hypocotyl showed a “lowpromotion and high-inhibition” effect. PLA₁ was involved in the regulation of roots. PLC was involved in the regulation of hypocotyl. The activities of different phospholipases changed greatly under different oridonin concentrations. The EL and MDA increased and were positively correlated with treatment concentration and duration. The stimulation of EL by 10 μmol·L^-1 of oridonin was regulated by PLA₂. The stimulation of EL by 60 μmol·L^-1 of oridonin was co-regulated by PLA₁ and PLA₂. PLA₁ and PLA₂ regulated the MDA accumulation under oridonin treatment. Our results showed that phospholipase involves in the allelopathy of diterpenoid oridonin to Arabidopsis thaliana. Different phospholipases have different roles in regulating the response of plant to oridonin during its growth.

Key words: fuel moisture, Canadian fire weather index system (FWI), Tahe, litter.