Effects of exogenous application of jasmomic acid and salicylic acid on the leaf and root induction of chemical defence in maize (Zea mays L.)

We studied (i). the contents of direct defence compounds (DIMBOA and phenolic acids), (ii). expression patterns of direct defence protein mediated genes (PR-2a and MPI) and (iii). expression of indirect defence volatile mediated genes (FPS and TPS) using HPLC and RT-PCR after the application of exogenous JA or SA for one week on the leaves or roots of maize variety ‘Gaoyou 115’. JA application on leaves systematically induced gene expression of MPI in the roots, but reduced the contents of DIMBOA, caffeic acid and syringic acid by 10.5%, 40.3% and 43.6% in the roots, respectively. However, JA application to roots induced gene expression of MPI and FPS in the leaves and also significantly increased the DIMBOA content (81.8%) in leaves. While SA application to the leaves systematically induced gene expression of MPI and FPS in the roots and decreased the contents of DIMBOA, coumaric acid, caffeic acid and syringic acid in roots by 45.8%, 64.2%, 60.2% and 72.4%, respectively. Yet SA application to roots only increased the DIMBOA content (95.8%) in leaves. These results suggested a close relationship between the induced defence in the leaves and roots of maize. JA or SA application on leaves can systematically trigger the defence response in the roots of maize, meanwhile JA or SA application to the roots can also systematically lead to the defence response in the leaves of maize.