Abstract: Biochemical and gene expression analysis methods were adopted to investigate the defensive substances and the defense-related genes expression in the roots and leaves of maize (Zea mays L.) cultivar Gaoyou 115 after underground treatment with 10, 50, 100 and 200 μmol·L-1 of jasmonic acid (JA) for 3〖KG-*2〗-〖KG-*7〗48 h, aimed to explore the timing- and concentration effect of belowground treatment with JA on the chemical defense response of maize. The chemical defense response of both treated roots and non-treated leaves of Gaoyou 115 was related to the time span of JA treatment and the concentration of JA. After treated with JA for 3〖KG-*2〗-〖KG-*7〗12 h, the gene expression of 〖STBX〗Bx9, PAL, PR-2a〖STBZ〗, MPI and FPS in treated roots was directly induced, resulting in an increase of DIMBOA content and a decrease of total phenol content, with the strongest induction effect detected at 100 μmol·L-1 of JA, followed by at 50 μmol·L-1, and at 10 μmol·L-1. The induction effect weakened with time. Underground treatment with JA indirectly affected the chemical defense response of non-treated leaves. After underground treatment with 50 μmol·L-1 of JA for 3 h, the gene expression of 〖STBX〗Bx9〖STBZ〗 and FPS in non-treated leaves was induced, which caused a consequent increase of leaf DIMBOA content. Within 6
〖KG-*2〗-〖KG-*7〗24 h of JA treatment, the gene expression of 〖STBX〗Bx9, PAL, PR-1〖STBZ〗, MPI and TPS in leaves was enhanced, while the leaf DIMBOA and total phenol contents were declined. For most of the parameters measured, the direct induction effect on roots was much more significant and started earlier than the indirect induction effect on leaves, and an increasing trend was observed in the induction effect with increasing JA concentration.

Key words: maize, jasmonic acid, belowground treatment, induced defense, timing- and concentration effect, Pinus armandii, ozone, radial structure, open-top chamber, dendrochronology, wood anatomy.