锰镉互作调控油菜镉累积与耐性的作用及其机理

Large areas of vegetable fields in china are now contaminated by cadmium (Cd) with low concentrations. Because the vegetable plots are scattered, and the planted vegetables have numerous varieties and short growth periods, it is difficult and expensive to remediating the Cd-contaminated vegetable fields by conventional technologies. Application of manganese (Mn) fertilizer is an effective way for remediation of Cd-contaminated vegetable fields, because it can significantly reduce shoots Cd concentrations in many crops, and is flexible, low-cost and quick, but little is known about the associated mechanisms. Therefore in this study, two genotypes of Brassica chinensis (pakchoi) with low and high Cd accumulation screened out by previous research will be selected as tested cultivars. A pot experiment will be carried out to study the effects of applying Mn fertilizers with different types and doses on Cd accumulation of pakchoi. Three hydroponic experiments will be conducted with different dosages of Cd and Mn, including the following contents: (1) the characteristics of Cd uptake, transfer, tissues and subcellular distribution, and chemical forms; (2) the responses of root morphology, photosynthesis, antioxidative systems involving enzymes and non-enzymes substances; (3) the expression responses of natural resistance-associated macrophage protein (Nramp) gene responsible for Cd and Mn uptake and transfer. Some advanced technologies will be adopted including non-invasive micro-test technique, fluorescence probe labeling and laser scanning confocal microscope imaging, and real time fluorescence quantitative PCR. Through the hydroponic experiments, the mechanisms on the accumulation and tolerance of Cd in pakchoi by the interaction of Mn and Cd will be investigated from the aspects of Cd uptake, transfer, detoxication, and gene regulation. The results of the study will highlight a new insight into elucidation of Cd and Mn interaction in plant, and also will provide an effective approach for the safe production in vegetable fields with low Cd contamination.

我国菜地镉污染呈现轻度、多发的趋势。由于蔬菜种植具有地块分散、品种多样以及生长期短的特点，常规修复技术治理难度大且成本高；施用锰肥可显著降低作物镉累积，将其用于修复菜地镉污染，具有灵活简便、成本低且起效快的优势，但相关机理研究较少。本项目以镉高、低累积基因型叶用油菜作为对象，通过盆栽和水培试验，采用非损伤微测、荧光探针-激光扫描共聚焦显微以及实时荧光定量PCR等技术，研究添加不同形态和浓度的锰对油菜镉累积的调控作用；研究锰、镉互作条件下，油菜体内镉吸收、转运及在组织、细胞、化学形态的分配特征；油菜根系形态、光合系统、酶促和非酶防御系统的生理响应机制；油菜体内锰、镉吸收转运相关的Nramp基因表达调控。从镉吸收转运、镉的解毒以及基因调控三个方面，探讨锰镉互作调控油菜镉累积和耐性的机理。本研究成果可丰富植物镉、锰交互作用理论，并为轻度镉污染菜地上蔬菜安全生产提供理论依据和技术支持。

我国菜地镉污染呈现轻度多发的趋势。施用锰肥可显著降低作物镉累积，将其用于修复菜地镉污染，具有灵活简便、成本低且起效快的优势。本项目以镉高、低累积基因型叶用油菜（寒绿和华骏）为对象，通过盆栽和水培实验，采用非损伤微测及PCR技术，研究添加不同形态和浓度的锰对油菜镉累积的调控作用；研究锰、镉互作条件下，油菜镉吸收、转运及细胞内分配特征，根系形态、光合及氮代谢系统的生理响应机制，锰、镉转运相关的Nramp基因表达调控。研究结果表明，土培条件下，喷施一定浓度的硫酸锰和乙酸锰降低华骏地上部镉含量的效果最佳；喷施硫酸锰和乙酸锰会使两个Nramp基因表达量显著下调，而喷施螯合锰则显著提高其表达量，这两个基因表达量变化与镉锰在油菜叶片亚细胞组分中的分配比例变化相吻合。水培条件下，缺锰处理会提高寒绿地上部镉含量，而对华骏地上部镉含量没有显著影响；镉在油菜体内优先分布在可溶组分和细胞壁，锰处理显著提高镉在寒绿地上部细胞壁、在华骏地上部可溶组分以及根部细胞壁中的分配比例；锰镉处理下油菜根部和茎基部镉离子流速可以部分解释锰调控油菜镉吸收转运的作用。镉胁迫下锰缺乏和过量处理会显著降低两种油菜地上部生物量和华骏根部生物量；锰镉处理下两种油菜根系形态参数受到显著抑制，但是二者在根系表面积分布上却有不同的响应规律；锰过量处理加重了镉胁迫对油菜叶片光合色素的抑制作用，锰缺乏和过量处理都能加重镉对油菜叶片光合参数的抑制作用，锰过量处理的影响更为严重；镉锰处理对两种油菜叶片亚硝态氮、铵态氮及脯氨酸含量都有提高作用，对硝态氮含量则有抑制作用，还显著降低氮代谢相关酶的活性，从而对油菜体内氮同化产生不同程度的抑制作用。上述成果揭示了锰镉互作影响油菜吸收、转运以及分配镉的微观机理及基因调控机制，阐明了根系形态和光合作用是锰影响油菜镉毒害的主导生理过程，并在此基础上提出了保障油菜在镉污染土壤上安全生产的锰肥施用方法。