Rice allelopathy induced by methyl jasmonate and methyl salicylate

Plants activate signaling system upon attack by insect herbivores and microbial pathogens. Methyl jasmonate (MeJA) and methyl salicylate (MeSA) are important signaling molecules which are able to induce plant defense against insect herbivores and microbial pathogens. This study tests the hypothesis that allelopathy is an active inducible defense mechanism of plants, and JA and SA signaling pathways may activate the allelochemical release. We found that exogenously applied MeJA and MeSA to rice (Oryza sativa L.) plants enhanced rice allelopathic potentials and accumulation of phenolics, increased enzymatic activities and gene transcription of PAL and C4H which are two key enzymes in the phenylpropanoid pathway. Aqueous extracts of the leaves of rice IAC165, a putative allelopathic variety showed 25%, 21% increase in inhibitory effects on root growth of barnyardgrass (Ehinohloa rus-galli L.), and 18%, 23% increase in inhibitory effects on the shoot growth after rice plants were treated with MeSA (5 mM) and MeJA (0.05 mM), respectively compared with the corresponsive control. Leaf aqueous extracts of rice Huajingxian1, a putative non-allelopathic variety treated with MeJA and MeSA showed 24% and 63% higher inhibition to the root length of barnyardgrass seedlings, respectively. The root exudates of rice plants treated with MeJA (0.05 mM) and MeSA (5 mM) for 48h significantly increased their inhibitory effects on root growth of barnyardgrass seedlings. 3, 4-hydroxybenzoic acid (HBA), vanillic acid (VA), coumaric acid (CMA) and ferulic acid (FA) in the leaves accumulated approximately to 5.3, 31.3, 2.2 and 1.7-fold higher levels in response to MeJA exposure, and accumulated to 3.3, 13.1, 2.0 and 2.2-fold higher levels in response to MeSA. At fourth leaf age，MeSA and MeJA treatments enhanced the PAL activity in rice leaves up to 52.3% and 80.1%, and C4H activity increased by 40.2％ and 67％, respectively. Gene transcription of PAL and C4H in rice leaves