茉莉酸是环境胁迫下植物产生防御反应的重要信号物质, 但它发挥生理作用的时间和浓度效应以及该效应在叶片和根系中差异性并不清楚。该文以‘高油115’玉米(Zea mays)为材料, 采用4种浓度(1、2.5、5和10 mmol·L^-1)的外源茉莉酸溶液涂施玉米幼苗叶片, 在3~48 h的不同时间内跟踪测定叶片和根系中的直接防御物质(丁布(DIMBOA)和总酚)含量及其合成调控基因(Bx1、Bx9和PAL)、直接防御蛋白调控基因(PR-1、PR-2a和MPI)和间接防御物质挥发物调控基因(FPS和TPS)表达的动态变化。结果表明, 外源茉莉酸处理对玉米叶和根系的化学防御反应具有显著的时间和浓度效应。茉莉酸处理玉米叶片后3~6 h就能诱导叶片中Bx9和PAL基因的表达, 使得丁布和总酚的含量显著增加, 且与处理浓度有呈正比的趋势, 随后诱导作用逐渐减弱; 茉莉酸处理还能明显诱导叶片中PR-2a和MPI基因的表达, 诱导作用分别持续到24和48 h; 在处理后3~6 h内, 高浓度茉莉酸处理对挥发物调控基因FPS表达起诱导作用, 而低浓度茉莉酸则对TPS基因的表达起诱导作用。此外, 茉莉酸处理玉米叶片还能间接影响到根系的防御反应, 但大部分检测指标表明间接诱导作用主要出现在处理后期(24~48 h)。例如, 在处理后48 h, 茉莉酸能系统增加根系中直接防御物质丁布和总酚的含量, 增强根系中防御相关基因PR-2a、MPI、FPS和TPS的表达, 并有随茉莉酸处理浓度的增加而增强的趋势。可见, 外源茉莉酸叶片涂施玉米幼苗对根系的间接诱导作用不如对叶片的直接诱导作用强; 叶片启动防御反应的时间较根系早; 随着处理浓度的增加, 茉莉酸对叶片和根系中防御反应的诱导作用有增强的趋势。

Aims Our objectives were to investigate temporal dynamics of the contents of direct defense chemicals (DIMBOA and total phenolics) and the expression levels of their corresponding key genes (Bx1, Bx9 and PAL), direct defense protein-related genes (PR-1, PR-2a and MPI), and indirect defense chemical volatile-related genes (FPS and TPS) in leaves and root systems of Zea mays seedlings under the application of exogenous jasmonic acid (JA) on leaf surface.
Methods Leaves of Z. mays cultivar Gaoyou 115 were treated with JA with concentrations of 1, 2.5, 5 and 10 mmol·L^-1. We examined contents of the defense chemicals and expression dynamics of their synjournal-mediated genes, direct defense protein-related genes and indirect defense chemical volatile-related genes in both leaves and roots from 3 to 48 h after the application.
Important findings Exogenous JA application resulted in significant timing and concentration effects on the chemical defense response. Gene expression of Bx9 and PAL in the leaves could be induced 3 to 6 h after treatment, resulting in an apparent increase in the content of DIMBOA and total phenolics. The increase was positively correlated with JA concentrations, but the inductive effect gradually decreased afterward. Gene expression of PR-2a and MPI in the leaves was also dramatically induced by JA up to 24 and 48 h, respectively. High JA concentrations induced the expression of FPS gene, whereas low JA concentrations had inducible effects on the expression of TPS after 3-6 h. In addition, JA treatment to leaves could indirectly induce the defense response in roots. Most parameters measured in the indirect induction mainly occurred in the later phase (after 24-48 h) of the treatment. For example, JA systematically increased the contents of DIMBOA and total phenolics in the roots and enhanced the expression of PR-2a, MPI, FPS and TPS genes in the roots 48 h after the treatment, showing a tendency of positive relationship with JA concentrations. These findings provided evidence that the indirect induction by JA application to Z. mays leaves on roots was not as strong as on leaves. Leaves started the defense response earlier than roots, and the induction of defense response both in leaves and roots was increased with increasing JA concentrations.