Volatilized myrcene inhibits growth and activates defense responses in rice roots

We aimed to analyze the phytotoxic effect of the allelopathic volatile myrcene on rice seedlings, particularly root growth, reactive oxygen species (ROS) generation, and activity of antioxidant enzymes and defense-related genes. Myrcene inhibited the growth of rice seedlings. The activity of ROS and lipoxygenase (LOX) was significantly increased with increasing myrcene concentration in roots and that of antioxidant enzymes was altered dose-dependently. The activity of superoxide dismutase and peroxidase was changed at 24 h after myrcene treatment in rice roots. Furthermore, the mRNA expression of three mitogen-activated protein kinase genes (OsMPK2, 3, and 4), WRKY transcription factor gene (OsWRKY71), LOX gene (OsLOX3), pathogenesis-related protein 1b gene (OsPR1b) and cyclin-dependent protein kinase inhibitor (OsCKI) was upregulated and that of cyclin genes OsCycA1;1, OsCycB1;1 and OsCycD1;1 was downregulated with myrcene treatment in rice roots. These results may provide new insights into the molecular basis of the allelopathic volatile response in plants.