土壤微藻对水稻吸收、转运和积累砷的影响及其机制

Inorganic arsenic is a class I human carcinogen, and the consumption of rice constitutes a major dietary source of inorganic arsenic for the population of China. Strategies to reduce arsenic accumulation in rice have received considerable attention recently. Many experimental studies have shown that soil microalgae are able to carry out reactions such as arsenite oxidation and methylation that result in changes in the mobilization and toxicity of arsenic in aquatic ecosystems. However, the roles of microalgae in the migration, transformation, uptake, and accumulation of arsenic in the soil–rice system have been seldom reported. To reveal the impact of microalgae on the uptake, transport, and accumulation of arsenic in rice, we will first perform isolation and characterization of arsenic-resistant microalgae from arsenic-polluted soils that have a major metabolic pathway for inorganic arsenic involving oxidation and/or methylation and result in a significant decrease in the accumulation of arsenic in rice shoots. Then, the following experiments with rice and microalgae will be carried out under both hydroponic and pot conditions: analysis of total arsenic, arsenic species, and non-protein thiol compounds in rice seedlings; determination of the critical parameters in rhizosphere and non-rhizosphere soils, including the chemical and physical properties, speciation and bioavailability of arsenic, and abundances of various genes involved in arsenic transformation; and analysis of the tissue and organ distributions of arsenic in rice. The results of this research will be of great significance for mitigating excessive arsenic accumulation in rice by using microalgae under field conditions and will have great importance for food safety.

无机砷是I类致癌物，而稻米是我国居民无机砷膳食暴露的主要来源，如何降低水稻籽粒中砷的积累和毒性是目前亟待解决的问题。作为土壤微生物区系的重要成员，一些微藻在纯培养条件下具备较强的亚砷酸盐氧化和/或甲基化能力，从而降低砷的移动性和毒性，但微藻在土壤—水稻系统中砷的迁移、转化、吸收和积累过程中所起的作用鲜有报道。本项目拟以微藻和水稻为研究对象，首先筛选出以氧化和/或甲基化为主要砷代谢途径并且能减少水稻地上部砷积累的耐砷土壤微藻，然后通过水培试验和土培试验，分析水稻体内砷的形态和含量、根系和地上部非蛋白巯基化合物含量，并从根际和非根际土壤理化性质、砷的赋存形态及有效性、砷转化基因丰度以及砷在水稻各组织器官的分布等方面揭示微藻对水稻吸收、转运和积累砷的影响及机制。本项目结果可为在大田条件下利用微藻阻控稻米砷积累提供一定的理论依据，对提高农产品质量安全有重要意义。

无机砷是I类致癌物，而稻米是我国居民无机砷膳食暴露的主要来源，如何降低水稻籽粒中砷的积累和毒性是目前亟待解决的问题。微藻在水稻土中分布广泛。然而，它们在水稻积累和转运砷的过程中所起的作用尚不明确。本研究以微藻和水稻为研究对象，首先筛选出能减少水稻地上部砷积累的的耐砷土壤微藻种类，然后通过水培试验和土培试验，运用建立的原子荧光非色谱分析法检测水稻体内砷形态和含量，并从根际土壤理化性质、砷的赋存形态及有效性以及砷在水稻各组织器官的分布等方面揭示微藻对水稻吸收、转运和积累砷的影响及机制。全文的主要结论如下：.1. 本研究通过优化原子荧光光谱仪的载流条件和四个不同的样品前处理步骤，建立了一种简单、灵敏、有效的稻米中四种砷形态（As(III)、As(V)、MMA(V)和DMA(V)）的非色谱分析方法。该方法的检出限较低，砷提取效率（96~104%）及回收率（95~100%）均较高，并且提取过程中没有发现砷形态的相互转化。.2. 水培条件下，添加固氮鱼腥藻能减少水稻对As(III)的吸收和转运、促进水稻对As(III)的外排，从而降低水稻地上部的砷积累。此外，固氮鱼腥藻能显著降低水稻根系巯基化合物的合成量，说明该藻能够缓解As(III)对水稻的毒害。.3. 盆栽持续性淹水条件下，接种微藻能显著促进水稻的生长及其对营养元素的吸收。接种固氮鱼腥藻对糙米中无机砷的含量没有显著影响，但显著减少了水稻根系和糙米中二甲基砷的浓度。水稻接种固氮鱼腥藻后，从根系向糙米转运砷的能力显著下降，这也导致糙米中总砷浓度的下降。接种微藻对土壤pH值、土壤砷形态和土壤营养元素的生物有效性有很大影响，而这些因素显著影响了水稻的生长、对营养元素的吸收，以及水稻体内砷的积累和转运。添加微藻对水稻根际甲基化微生物群落结构影响不大。本研究的结果表明，在砷污染水稻土中接种藻类是促进水稻对营养元素吸收、减少砷从根系向糙米转运的行之有效的策略。