Duration and dosage effect of chemical defense in maize (Zea mays) mediated by exogenous ethephon

In this study, the amount of ethylene and its key biosynthesis genes (ACS and ACO) expression, typical allelochemical hydroxamic acid (DIMBOA) concentration and the key regulation genes (BX₁ and BX₉), as well as the dynamic expression and time of relevant defense key genes of secondary substance metabolism processes were compared in ethephon treatments of different concentration and duration. The main objective was to build further understanding into the role of ethylene signal pathway in the process of induced defense in maize. The results show that ethylene signal pathway occurs during induced chemical defense mechanism in maize. The amount of ethylene released from the second leaf and the concentration of DIMBOA significantly increase in maize after treatment for 12 h, but both variables decrease significantly after 24 h.ACS, ACO andBX₉ gene expression upregulates at 12 h and 24 h, but BX₁ gene completely fails to be expressed. Meanwhile, DIMBOA decreases when concentration of exogenous ethylene is high (40～60 μL·L^-1). Exogenous ethylene treatment leads to high expression of proteinase inhibitor MPI defense gene, and the expression gets stronger with increasing concentration of exogenous ethylene. However, exogenous ethylene dose not influence FPS and TPS expression. In conclusion therefore, exogenous ethephon treatment induces chemical defense in maize, but ethylene content in maize is a negative feedback regulation mechanism that variously leads to metabolic reconfiguration and activation of direct and indirect responses of defense genes.