National Key Laboratory of Wheat and Maize Crop Science, Key Laboratory of Regulating and Controlling Crop Growth and Development Ministry of Education, Henan Agricultural University, Zhengzhou, Henan, 450046, China.
Chongqing Jinfo Mountain Karst Ecosystem National Observation and Research Station, School of Geographical Sciences, Southwest University, Chongqing, 400715, China.
Environ Pollut. 2022 Aug 15;307:119488. doi: 10.1016/j.envpol.2022.119488. Epub 2022 May 18.
Nitric oxide (NO) is an important phytohormone for plant adaptation to mercury (Hg) stress. The effect of Hg on lignin synthesis, NO production in leaf, sheath and root and their relationship were investigated in two members of the grass family - wheat and maize. Hg stress decreased growth and lignin contents, significantly affected phenylpropanoid and monolignol pathways (PAL, phenylalanine ammonia-lyase; 4-coumarate: CoA ligase, 4CL; cinnamyl alcohol dehydrogenase, CAD), with maize identified to be more sensitive to Hg stress than wheat. Among the tissue types, sheath encountered severe damage compared to leaves and roots. Hg translocation in maize was about twice that in wheat. Interestingly, total NO produced under Hg stress was significantly decreased compared to control, with maximum reduction of 43.4% and 42.9% in wheat and maize sheath, respectively. Regression analysis between lignin and NO contents or the activities of three enzymes including CAD, 4CL and PAL displayed the importance of NO contents, CAD, 4CL and PAL for lignin synthesis. Further, the gene expression profiles encoding CAD, 4CL and PAL provided support for the damaging effect of Hg on wheat sheath, and maize shoot. To validate NO potential to mitigate Hg toxicity in maize and wheat, NO donor and NO synthase inhibitor were supplemented along with Hg. The resulting phenotype, histochemical analysis and lignin contents showed that NO mitigated Hg toxicity by improving growth and lignin synthesis and accumulation. In summary, Hg sensitivity was higher in maize seedlings compared to wheat, which was associated with the lower lignin contents and reduced NO contents. External supplementation of NO is proposed as a sustainable approach to mitigate Hg toxicity in maize and wheat.
一氧化氮（NO）是植物适应汞（Hg）胁迫的重要植物激素。研究了两种禾本科植物——小麦和玉米在汞胁迫下对木质素合成、叶片、叶鞘和根中 NO 产生及其关系的影响。Hg 胁迫显著降低了生长和木质素含量，严重影响了苯丙氨酸途径和肉桂醇途径（PAL、苯丙氨酸解氨酶；4-香豆酸：CoA 连接酶，4CL；肉桂醇脱氢酶，CAD），玉米对 Hg 胁迫的敏感性大于小麦。在组织类型中，叶鞘比叶片和根受到更严重的损伤。玉米中 Hg 的转运量约为小麦的两倍。有趣的是，与对照相比，Hg 胁迫下产生的总 NO 显著减少，小麦和玉米叶鞘分别最大减少了 43.4%和 42.9%。木质素和 NO 含量或 CAD、4CL 和 PAL 三种酶活性之间的回归分析显示了 NO 含量、CAD、4CL 和 PAL 对木质素合成的重要性。此外，编码 CAD、4CL 和 PAL 的基因表达谱为 Hg 对小麦叶鞘和玉米茎的损伤效应提供了支持。为了验证 NO 减轻玉米和小麦中 Hg 毒性的潜力，在添加 Hg 的同时补充了 NO 供体和 NO 合酶抑制剂。表型、组织化学分析和木质素含量表明，NO 通过提高生长和木质素合成和积累来减轻 Hg 毒性。总之，与小麦相比，玉米幼苗对 Hg 的敏感性更高，这与较低的木质素含量和减少的 NO 含量有关。建议外部补充 NO 作为一种可持续的方法来减轻玉米和小麦中的 Hg 毒性。
