[ 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 .