小麦对PAEs污染的防御应答机制

Phthalic acid esters (PAEs) are ubiquitous contaminants in the soil. The contamination of PAEs to environment has become more severely. Very limited research deals with corresponding responses of food crops in phthalates polluted soil until now. Taking di-n-butyl phthalate (DBP) and bis (2-ethylhexyl) phthalate (DEHP) as typical contaminants in this research project, the difference with regard to effects of mineral humic acid and small molecule organic acid on the of bioavailability of PAEs in the alluvial soil, cinnamon soil and brown soil will be studied. On the above basis, response pattern of the wheat on PAEs will be conducted at physiological and biochemical level, cell/subcellular and molecular level, combining with HPLC-MS, Q-TOF analytical technology to ascertain metabolites of PAEs in soil and wheat in order to reveal the pathways and mechanisms of absorption, transport and metabolism of DBP and DEHP. This project will also focus on toxic impacts of various forms DBP/DEHP in soils to clarity the defense response mechanism of the wheat against DBP/DEHP contamination. The implementation of this project will not only provide a deep insight to the toxical effect of PAEs in soil-crop system, but also provide new ideas of preventing PAEs invasion into the food chain.

邻苯二甲酸酯（PAEs）在我国土壤中广泛存在且污染程度、强度日益加重。但迄今为止，人们对PAEs污染土壤上粮食作物对其的响应机制认识薄弱。因此，本项目以邻苯二甲酸二丁酯（DBP）和邻苯二甲酸双（2-乙基己基）酯（DEHP）为典型污染物，考察不同矿物、腐殖质、小分子有机酸对DBP、DEHP在潮土、褐土和棕壤上生物有效性的影响差异；在此基础上，采用根箱试验，从生理生化水平、细胞/亚细胞水平及分子水平系统研究小麦对DBP、DEHP的响应规律；同时结合高效液相色谱-质谱（HPLC-MS）、飞行质谱（Q-TOF）等分析技术，确定PAEs在小麦根际土壤及小麦体内的代谢产物，揭示小麦吸收、转运与代谢DBP、DEHP的途径和机制，阐明小麦对此类外源污染物的防御应答机制。本项目的实施不仅为认识PAEs在土壤-作物系统的毒理学效应提供新证据，还为屏蔽PAEs进入食物链提供新思路。

项目研究了邻苯二甲酸酯（PAEs）的生物有效性和小麦对邻苯二甲酸二丁酯（DBP）和邻苯二甲酸双（2-乙基己基）酯（DEHP）胁迫的响应机制。研究结果表明：（1）不同温度、pH、矿物和小分子有机酸条件下，DBP在土壤和矿物中的吸附等温线均符合Freundlich模型拟合，吸附过程兼具物理和化学作用，且物理作用占主导地位，主要吸附作用力为氢键、阳离子交换作用和偶极矩。（2）DBP、DEHP 胁迫下苗期、拔节期和孕穗期小麦的净光合速率，最大光化学效率，电子传递速率，叶绿素a与总叶绿素含量降低，而胞间二氧化碳浓度增加。这表明小麦叶片净光合速率的降低是由于非气孔限制所致。最后，光合作用的降低导致不同时期小麦叶片、根系和籽粒生物量随PAEs浓度增加而降低。（3）DBP和DEHP胁迫下，不同时期小麦叶片、根部和籽粒中超氧阴离子自由基（O2.-）及H2O2含量明显增加。为了消除过量活性氧（ROS），小麦组织中抗氧化酶活性增强。但由于ROS的产生速率大于清除速率，导致小麦叶片和根系细胞膜结构遭到损伤。小麦籽粒中蓄积的PAEs诱导抗氧化酶基因上调（细胞色素P4503A4和过氧化物酶）和活性增加。此外，籽粒中元胞糖酶I基因上调，表明细胞发生程序性死亡。（4）不同时期小麦叶片、根部和成熟期籽粒中DBP、DEHP及其代谢产物的浓度与胁迫浓度呈正相关，且呈现籽粒>茎>叶>根的规律。（5）高通量测序分析表明，DEHP污染潮土和棕壤的可操作分类单元丰富度和细菌多样性降低，而DEHP污染褐土和DBP污染土壤的操作分类单元丰富度和细菌多样性无明显变化。（6）随着土壤中PAEs胁迫浓度升高，小麦根际土壤中PAEs含量增加；而随着小麦的生长，根际土壤中DBP和DEHP的含量明显降低。此外，苗期和拔节期小麦根际土壤中MBP和MEHP的含量明显增加，孕穗期明显降低。成熟期时，小麦根际土壤中未检测到MBP和MEHP。