甘薯镉污染预防品种筛选及其块根低量积累镉的生理机制研究

Production of cadmium (Cd) pollution-safe cultivars (PSCs), that is, the crop cultivars whose edible parts accumulate Cd at a low enough level for safe consumption when grown in slightly to moderately Cd-contaminated soils, has been used as an effective tool to minimize the Cd accumulation in agricultural products. Understanding the difference of Cd accumulation among cultivars within the same species is crucial for breeding Cd-PSCs. Sweet potato is the fourth most important food crop in China and has high Cd-accumulating ability. In this project, a pot experiment will be conducted to screen for Cd-PSCs and high-Cd cultivars from sweet potato cultivars widely cultivated in our country. On this basis, in order to elucidate the physiological mechanisms of low Cd accumulation in sweet potato Cd-PSCs, the differences, including Cd uptake dynamics during the whole growth stage, characteristics of rhizosphere soil and root morphology and structure, transport of Cd via xylem and phloem and subcellular distribution and chemical form of Cd, will be investigated among a typical Cd-PSC, a typical high-Cd cultivar and their self-grafted and reciprocally grafted plants. And it will be also investigated how roots and shoots influence plant total Cd uptake and Cd accumulation in storage roots. The aims of this project are to screen out Cd-PSCs from widely cultivated sweet potato cultivars and to clarify the mechanisms of low Cd accumulation in storage roots of Cd-PSCs. Results from this research will provide scientific information for the selection and breeding of crop Cd-PSCs.

筛选和应用可食部分具有低镉积累能力的农作物镉污染预防品种是解决中、轻度镉污染土壤上农产品安全生产的一条重要途径，而深入开展农作物品种间镉积累能力差异的机理研究是培育镉污染预防品种的首要基础。甘薯是我国第四大粮食作物，其块根积累镉的能力较强。本项目拟从我国广泛栽培的甘薯品种中筛选出镉污染预防品种和高镉品种。在此基础上，研究镉污染预防品种、高镉品种以及二者自我嫁接和相互嫁接植株全生育期根系吸收镉动态变化的差异，根际土壤特征和根系形态结构的差异，根系木质部和茎叶韧皮部运输镉能力的差异以及不同器官中镉的亚细胞分布和化学结合形态的差异，分析甘薯根系和茎叶对植株吸收镉能力的影响及其对块根镉含量的贡献，旨在从镉的吸收和转运两方面阐明甘薯镉污染预防品种块根低量积累镉的生理机制。本项目的实施有望获得一批甘薯镉污染预防品种并揭示其块根低量积累镉的规律，从而为农作物镉污染预防品种选育技术的形成提供科学依据。

本项目以甘薯为研究对象，目的是从30个甘薯品种中筛选出Cd污染预防品种和高Cd品种，并阐明Cd污染预防品种块根低量积累Cd的机理。研究发现甘薯品种间块根Cd含量存在显著差异，并成功筛选到4个高Cd和4个Cd污染预防品种。甘薯块根Cd含量与Cd从细根向块根的转运以及从茎叶向块根的转运有关。Cd污染预防品种根细胞壁固定Cd的能力较高Cd品种强。而且，Cd污染预防品种根中乙醇提取态Cd低于高Cd品种，醋酸提取态Cd则高于高Cd品种，从而减少了Cd向地上部转运。低Cd胁迫下， Cd污染预防品种的根长、比根长和根尖数均小于高Cd品种，且这三个参数与茎叶Cd含量显著正相关，这可能有助于Cd污染预防品种减少Cd从根向茎叶转运。此外，高Cd与Cd污染预防品种的根际土壤可交换态Cd含量并无显著差异，且根尖分泌的低分子量有机酸与Cd胁迫水平有关。Cd在植物体内的转运分析显示，高Cd品种能更快地将Cd从根通过木质部向地上部转运。品种间相互嫁接试验发现，接穗品种不仅影响块根的Cd含量而且影响细根的Cd含量；土壤Cd含量空间异质性试验发现块根中积累的Cd来源于细根和茎叶。因此，甘薯品种间块根Cd含量差异的形成可能与木质部和韧皮部中Cd的运输均有关。