水稻体内镉的韧皮部运输机制及其与籽粒镉积累动态的关系

Heavy metal such as cadmium (Cd) pollution of agricultural soils is a severe problem in China. A better understanding of mechanisms involved in Cd accumulation of rice grains facilitates the development of strategies to reduce Cd contents in rice for human health. The aim of this study is to investiagate how Cd is tranlocated from leaves and stems to grains by phloem during flower and seed development stages by using new methodology (Nano-XRF, µ-XAS, LA-ICPMS), combined with isotope tracing. Mainly, the project will be focused on: 1) cellular distribution pattern and speciation of Cd in rice plant tissues including node, flag leaf, and panicle; 2) subcellular distribution patterns and speciation of Cd in the phloem tissues; 3) cellular and subcellular localization of Cd in the flower and grains at different development stages by 2-D and 3-D XRF imaging; 4) speciation of Cd in the flower and grains at different development stages, with the aim of increasing our understanding of the processes involved in 1) phloem tranlsocation of Cd from stem and leaf tissues to grains, and 2) movement and storage of Cd wihtin the flower and grain tissues of rice. This project activity may help to elucidate the mechanisms involved in Cd accumulation in rice grains, thus to facilitate the promotions of stragies development for protecting human from Cd toxicity through diets.

我国镉污染农田土壤量大面广，探明水稻籽粒镉的积累机制是阻控镉从污染土壤向稻米富集以保障我国居民健康的关键所在。本项目围绕水稻生育后期（籽粒形成关键期）镉从营养器官向生殖器官的转运途径这一关键科学问题，在前期突破植物体内镉原位示踪与定位技术瓶颈的基础上，以镉低/高积累水稻基因型为对象，综合运用Nano-XRF、µ-XAS、同位素示踪等技术，分析水稻生育后期关键部位（节点、剑叶、穗梗）镉的赋存形态与微区分布特征，韧皮部不同位点上镉的赋存形态差异与亚细胞分布特征，明确水稻体内镉的韧皮部运输形态与特征；研究水稻颖花和不同发育期颖果（籽粒）中镉的细胞与亚细胞定位、三维构象与赋存形态，阐明镉在籽粒内部的运移规律、分布特征与储存方式，以期原位解析水稻体内镉的韧皮部运输机制及其与籽粒镉积累动态的关系，为全面揭示镉从土壤向水稻籽粒积累过程的关键机制、解决我国中轻度镉污染土壤的稻米安全生产问题奠定基础。

我国镉污染农田土壤量大面广，已严重危及我国稻米等主要粮食的生产安全，探明水稻籽粒镉的积累机制，是降低稻米等农产品对重金属镉的积累，减少其通过食物链向人体转移以保障我国居民健康的关键所在。本项目以前期筛选到的镉低/高积累水稻基因型为研究材料，重点围绕“土壤-水稻系统中籽粒镉的积累过程及调控因素”展开研究，首先采用微生物组学技术，构建了土壤-植物系统重金属根土界面过程与生物有效性研究的原位解析技术体系，从而明确了水稻根际特异微生物对其吸收与累积镉的潜在调控作用，并进一步对镉污染土壤中添加生物炭，证实了外源添加生物炭可通过改变土壤中微生物群落来缓解土壤介质中的高镉胁迫，降低水稻籽粒镉积累，阐明了水稻根际的微生物调控作用与籽粒镉积累之间的关系；在此基础上，采用金属组学分析技术、现代分子生物学等技术研究了重金属在镉低/高积累水稻根系和地上部中的吸收、运输、区隔与再转运特征，揭示了水稻根系（尤其是侧根）木质部对镉的快速转运能力是其籽粒高量积累镉的重要因素之一，并明确了节点中镉的韧皮部再转运过程对水稻籽粒中镉积累的关键调控作用，发现水稻籽粒中镉的存储方式存在着与其他元素截然不同的独特机制。上述研究成果为解答水稻籽粒中镉积累的来源与归趋问题，全面揭示土壤-水稻系统中籽粒镉积累的关键机制、为解决我国中轻度镉污染土壤上稻米的安全生产问题提供科学依据。本项目研究结果共发表4篇高质量学术论文，影响因子合计22.7，另投稿或拟投稿SCI论文4篇。.