砷超积累植物蜈蚣草根际植酸-植酸酶的生物界面过程与机制

Arsenic (As) contaminated soil is of environmental concern and its remediation has become a international scientific issue and a major national requirement. However, the soil-organism interface reactions and/or processes in rhizosphere of the typical As-hyperaccumulator P. vittata and its effects on As-contaminated soils phytoremediation efficiency are limited studied. To elucidate the mechanism by which rhizosphere interface reactions influence soil As transformation and the subsequent bioavailability thus the plant uptake and remediation, indoor simulation experiment under controlled environment and field soil in-situ analysis are introduced in the present project. Typical root exudates phytic acid (phytate) and phytase of P. vittata are chosen as the focuses. The aims of the project are to: (1) examine the characteristics of P. vittata phytase activity compared to those of wheat and microorganisms, evaluate the hydrolyzation efficiencies of P. vittata phytase towards multiple phytate salts, figure out the key parameters monitoring phytase activity, and identify the limiting step for phytate-P acquisition by plant roots; (2) examine the effect of common organic acids on phytate-phytase interface reactions and soil As distribution, transformation and plant uptake and accumulation, identify the most significant organic acid and its concentration in affecting the transformation process, and evaluate the efficiency of rhizospheric application of organic acids in facilitating phytate-P assimilation and As uptake by plants. The result and information obtained from the project may help to better understand the mechanisms for rhizosphere interface reactions-mediated nutrients and/or contaminants mobilization, transformation and redistribution, and provide theoretical and technical supports for improving soil endogenous phytate plant assimilation and As-contaminated soil remediation efficiencies, and provide a reference for soil pollution control, soil quality protection and remediation of other similar soils facing heavy metals pollution problems.

土壤砷污染是土壤科学研究的热点，其修复治理已成为国家重大现实需求，但关于修复植物蜈蚣草根际土-生微界面过程及其对修复效率的影响机制尚缺乏系统研究。本项目以修复模式植物蜈蚣草为研究对象，重点研究根际植酸-植酸酶生物界面过程及砷活化效应与修复机制，拟解决如下两个科学问题：1）探明修复植物根系植酸酶活性特征及根际植酸植物利用关键过程；2）揭示有机酸介导的根际植酸-植酸酶界面过程与砷活化效应及机制。本项目拟通过室内控制模拟试验，准确判定蜈蚣草植酸酶活性特征及作用过程影响机制；精准识别限制植酸植物利用的关键过程；探明根际有机酸对植酸-植酸酶微界面过程、土壤砷形态转化、再分配与释放特征的影响，并探明根际施加有机酸的修复效率及机制。研究成果可为提高土壤内源难利用态有机磷的利用效率和强化砷污染土壤修复效率提供科学依据，为面临重金属污染的其他类型土壤的修复与安全利用提供技术支撑和参考借鉴。

土壤砷污染是土壤科学研究的热点，其修复治理已成为国家重大现实需求，但关于修复植物蜈蚣草根际土-生微界面过程及其对修复效率的影响机制尚缺乏系统研究。本项目通过开展：1）植物植酸酶提取与活性测定；2）pH、温度、重金属离子对植酸酶活性的影响；3）不同pH值植酸酶的酶促反应动力学；4）腐殖质对蕨类植酸酶活性及酶促反应速率的影响，表明：1）(NH4)2SO4盐析法提取3种蕨类植物的植酸酶，盐浓度为50-90%时，植酸酶活性均表现为PE>PM>PV，在盐浓度为80%时达最大值。PE、PM、PV酶活分别为10.2-11.1、10.1-10.6、8.6-10.6 U/g；2）pH=4.0–6.0时，可保持相对酶活，pH=2–3和7–10时，植酸酶失活。pH=5.5时酶活达最大值，PV、PM和PE酶活分别为9.4、10.4和11.0 U/g。30-70℃时，植酸酶活性呈上升趋势，表现为PE>PM>PV>SP，40℃时均达最大反应酶活，分别为12.6、11.6、11.3和10.2 U/g，且植酸酶活性均随Zn、Cu、Fe、Ca浓度升高而降低，酶活抑制作用表现为Zn>Cu>Fe>Ca；3）3种植酸酶反应速率整体表现为PE>PM>PV，且均随pH和底物浓度升高呈先上升后下降趋势，并分别在pH=5.5和5 mmol/L时达最大酶促反应速率，为11.9、11.3、10.6 µmol/(min·g)，其中PV植酸酶对环境pH变化的耐受性较好。此外，植酸酶在低底物浓度时反应速率较低，提高底物浓度可极大提高其反应速率。3种植酸酶的Km、Vmax和Km/Vmax值均在pH=4-6时随pH值升高呈先上升后下降趋势，pH=5.5时达最大值。植酸酶在pH=5.5亲和力表现为PV>PE>PM，Vmax值表现为PE>PM>PV，Km/Vmax值表现为PM>PE>PV；4）SP、PV、PM和PE植酸酶等电点分别为5.1、4.9、5.0和5.2，在最适pH=5.5时所带负电荷量顺序为PE<SP<PM<PV。三种植酸酶活性均随富里酸（HA）浓度升高而下降，HA浓度为5 mg/L时，PV、PE、PM酶活达最低值，分别降低47.6%、45.5%和45.9%。研究成果可为提高土壤内源难利用态植酸磷的利用效率提供科学依据和技术参考。