丛枝真菌对镉胁迫小麦GSH代谢通路解毒能力的调节机制

Cadmium (Cd) pollution in soil threatens the quality and safety of wheat (Triticum aestivum). The toxicity of Cd to plants is mainly caused by excess production of reactive oxygen species (ROS) such as singlet oxygen (1O2), superoxide radicals (O2•−), hydrogen peroxide (H2O2), hydroxyl radicals (•OH) and methylglyoxal (MG). These ROS are highly active and toxic. They destroy protein, nucleic acid and cell membrane, and interfere with the normal metabolism in cells. MG is both a mutagen and a genotoxic agent. GSH takes part in the control of H2O2 levels through the ascrobat acid and glutathione cycle (AsA-GSH). It can also function directly as a free radical scavenger by reacting with 1O2, O2•− and •OH. MG can be detoxicated by glyoxalase pathway in plants. PCs are synthesized from GSH, and they act as chelators, and are important for heavy metal detoxification. GST acts by catalyzing the conjugation of GSH with electrophilic, often hydrophobic toxic compounds to form derivatives that can be secreted from the cell, sequestered in the vacuole, or catabolized. The endurance of plants to heavy metals can be improved by arbuscular mycorrhizal fungus, but it is not clear that after inoculation arbuscular mycorrhizal fungus to wheat under Cd stress how AsA-GSH cycle system effects Cd accumulation and detoxification. Therefore, this research will study effects of inoculation arbuscular mycorrhizal fungus on the content of cadmium in wheat grown in Cd contaminated soil, effects of inoculation arbuscular mycorrhizal fungus on content of ROS and MG, detoxification levels of PCs and GST, and proteome expression and gene transcriptome expression of wheat under Cd stress. The study will reveal the effects of inoculation arbuscular mycorrhizal fungus on detoxification levels of GSH metabolism pathway in wheat under Cd stress.

土壤Cd污染威胁小麦质量安全。Cd对植物毒性主要是产生过量活性氧（ROS）和丙酮醛（MG）。植物可通过抗坏血酸谷胱甘肽（AsA-GSH）循环清除ROS，也可通过依赖GSH的酮醛转位酶途径解毒MG，还可利用植物螯合素（PCs）解毒Cd，而PCs以GSH为底物合成。同时，GSH在谷胱甘肽S-转移酶（GST）催化下，也可解除Cd毒性。丛枝真菌可改善植物对胁迫的耐性，但对Cd污染土壤小麦Cd积累及解毒机制尚不清楚。本项目研究：①丛枝真菌对Cd污染土壤小麦Cd含量的影响，②丛枝真菌对Cd胁迫小麦ROS和MG含量的影响，③丛枝真菌对Cd胁迫小麦ROS和MG清除能力及PCs和GST解毒能力的影响，④丛枝真菌对Cd胁迫小麦蛋白质组表达的影响，⑤丛枝真菌对Cd胁迫小麦基因转录组表达的影响。研究可阐明丛枝真菌对Cd胁迫小麦GSH代谢途径解除和耐受Cd毒性的分子机制，为降低Cd污染土壤小麦Cd含量提供理论依据。

土壤Cd污染威胁小麦质量安全。Cd胁迫造成过量细胞毒性物质ROS和丙酮醛（MG），引起细胞氧化损伤。植物可通过抗氧化酶、抗氧化剂清除过量ROS、解毒MG。丛枝菌根真菌（Glomus mosseae，GM）可改善植物对胁迫的耐性，但GM对Cd胁迫小麦GSH代谢通路的调节机制尚不清楚，本试验通过室内盆栽幼苗和大田全生育期盆栽进行研究。Cd胁迫接种GM与同等浓度胁迫未接种相比：（1）根际球囊霉素及其中的Cd含量均显著升高，土壤中Cd的生物有效性降低，根系Cd含量增加，叶片、籽粒中Cd含量减少；（2）叶片微量元素Fe、Mg和Zn含量增加，叶绿素含量升高，光化学最大效率（Fv/Fm）、净光合速率增加、提高小麦生物量；（3）与抗逆胁迫相关的SA、JA和ABA含量下降，IAA含量上升；（4）Cd胁迫产生的过量H2O2、MDA、MG含量和O2•−产生速率均显著下降；（5）SOD、POD、CAT活性降低，但GSH-AsA循环中的抗氧化酶活性增加、相关基因表达上调，抗氧化剂含量提高。（6）转录组表达显示，338个基因在胁迫接种GM后表达上调，316个基因在胁迫接种GM后表达下调，包括抗氧化胁迫相关基因、与逆境胁迫相关转录因子基因、植物激素信号转导相关基因等。（7）蛋白质组学显示，差异蛋白包括超氧化物歧化酶、半胱氨酸合酶、叶绿素 a-b 结合蛋白、S-腺苷甲硫氨酸合酶等。差异蛋白GO富集分析表明，上调蛋白包括抗坏血酸代谢，过氧化物酶体，叶绿素代谢、光合生物中的碳固定，下调蛋白包括硫代谢、谷胱甘肽代谢、抗坏血酸和醛糖酸盐代谢、溶酶体、半胱氨酸和蛋氨酸代谢、光合作用-天线蛋白代谢等。研究结果表明，Cd胁迫下接种GM通过降低根际球囊霉素影响Cd的生物有效性、改变Cd在小麦各器官的分布、调节相关基因的表达水平、调节相关蛋白质表达水平、影响抗氧化酶活性、抗氧化剂含量、减少H2O2、MDA、MG的毒性，从而实现解除Cd的毒性。本研究结果可为降低Cd污染土壤小麦Cd毒性提供理论依据。