Abstract:

【Objective】 The objective of this investigation was to study whether exogenous jasmonic acid treatment to the aboveground (or underground) could systemically affect the defense response of underground (or aboveground) in corn, and to find out whether the effect of defense response was related with the signal transduction of jasmonic acid. 【Method】 Both chemical analysis and gene expression analysis were employed to study the role of jasmonic acid on the induced defense response of aboveground and underground in corn cultivar Gaoyou 115 by comparative studies prior to using the inhibitor salicylhydroxamic acid (SHAM) in jasmonic acid signaling pathway. 【Result】 The results showed that exogenous jasmonic acid applied to the aboveground of corn could systemically affect the content of defense chemicals and the expression of defense-related genes of underground, and vice versa. Jasmonic acid treatment to either aboveground or underground could result in much more obvious defense response in the leaves as compared to the roots, while jasmonic acid treatment to the aboveground could lead to much stronger induction in the same parts of corn than to the underground. Through activating the synthesis of jasmonic acid itself, aboveground application of jasmonia acid could induce the expression of Bx1, Bx9, PAL, PR-1, MPI, FPS and TPS genes, increase DIMBOA content and decrease caffeic acid content in leaves; on the other hand, the systematic induction of gene expression of Bx6, Bx9、PAL and PR-2a, increase of contents of coumaric acid and caffeic acid, and decrease of syringic acid content in the roots were related with the activating of jasmonic acid synthesis in the aboveground. Likewise, after the underground of corn was treated with jasmonic acid, the induced expression of Bx6, PR-2a and MPI genes as well as the decrease of total phenolics in the roots were achieved through activating the synthesis of jasmonic acid itself; while the indirect induction of expression of Bx6, Bx9, PAL, FPS and TPS genes as well as the increase in the contents of DIMBOA, coumaric acid, caffeic acid, and syringic acid in the leaves were related with the activating of jasmonic acid synthesis in the underground. 【Conclusion】 These findings indicate that exogenous jamonic acid application to the aboveground can systematically affect the defense response in the underground of corn, and vice versa. Leaves show much stronger induced defense to jasmonic acid application than roots. Application of jasmonic acid to the aboveground of corn has stronger induction than to the underground. The effects of jasmonic acid treatment to aboveground or underground on the defense response in treated parts of corn are acquired mainly by activating the synthesis of corn internal jasmonic acid, and the effects on the defense response in non-treated parts are related with the activating of jasmonic acid synthesis in the treated parts.

Key words: corn, jasmonic acid, induced defense, aboveground and underground, defense chemicals, defense-related genes