[Timing- and concentration effect of belowground treatment with jasmonic acid on maize seedlings chemical defense response].

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 micromol x L(-1) of jasmonic acid (JA) for 3-48 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 3-12 h, the gene expression of Bx9, PAL, PR-2a, 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 micromol x L(-1) of JA, followed by at 50 micromol x L(-1), and at 10 micromol x 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 micromol x L(-1) of JA for 3 h, the gene expression of Bx9 and FPS in non-treated leaves was induced, which caused a consequent increase of leaf DIMBOA content. Within 6-24 h of JA treatment, the gene expression of Bx9, PAL, PR-1, 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.