Analysis at the nanoscale:addressing key problems in plant sciences with advanced analytical techniques

砷（As）是一种致癌和有毒元素。饮用水的天然砷污染是许多地区接触该元素的主要来源，在孟加拉国、西孟加拉以及中国和美国的部分地区尤为普遍。孟加拉国和西孟加拉的饮用水砷污染被描述为历史上最大规模的人口中毒事件，数百万人受到影响。水稻是砷流行区的主要食物之一，砷污染水的灌溉导致水稻中砷含量升高。欧洲食品安全局呼吁减少砷的摄入量。这只能通过更好地了解水稻植株中As吸收和运输的途径来实现，这是我项目第一部分的目的。这是一个真正具有国际意义的问题，只能通过跨学科的方法来解决。小麦籽粒贮藏蛋白在食品加工中具有极其重要的意义，因为它们在面团中形成粘弹性网络，捕获糖发酵过程中形成的二氧化碳气泡，导致面团在烘焙时膨胀。这些蛋白质沉积在谷粒的淀粉质胚乳区域，在碾磨时得到白色面粉部分。然而，淀粉胚乳是不均匀的组织，在淀粉，蛋白质和细胞壁多糖的含量和组成的明显梯度。这些梯度对谷物加工有影响，因为它们可以允许生产具有特定组成和加工特性的面粉级分。然而，它们也是理解胚乳发育的控制和决定加工特性的面筋蛋白的合成的基本兴趣。本项目将使用NanoSIMS -最先进的高分辨率二次离子质谱法-定位As在水稻植株的节点，在茎中，溶质被分成两股，一股控制叶片的吸收，另一股控制米粒的吸收。已经确定了几种转运蛋白控制As吸收到粮食中，我将比较野生型水稻植株与突变体的节点处痕量As的分布，这些突变体缺失这些特定的转运蛋白基因，因此阻止As的吸收。在我的项目的第二部分，我将使用NanoSIMS检测同位素的能力来研究蛋白质在发育中的小麦籽粒中的分布。小麦植株将被喂以用于氮肥的化合物，这些化合物已被同位素掺入15 N。植物无法区分天然存在的14 N和天然丰度较低的15 N，因此其在谷物中的分布可用于直接推断蛋白质合成机制。这项研究将主要在牛津大学材料系进行。这是一个高度合作的项目，将涉及植物生理学、环境科学、作物营养和谷物结构和成分领域的科学家，以开发新的方法，提高对植物中关键元素吸收和沉积的理解。用于西姆斯分析的生物样品的样品制备是困难和复杂的。牛津布鲁克斯大学的生命科学系在为TEM和我们发现的NanoSIMS分析准备生物材料方面有很多专业知识。样品将在Rothamsted Research生长，在牛津布鲁克斯大学制备，关键元素的分布将由牛津材料系的NanoSIMS确定。强有力的合作联系将被用来解释这些结果，使植物科学的许多方面的科学知识的影响。

Arsenic (As) is a carcinogenic and toxic element. Natural contamination of drinking water with As is the main source of exposure to this element in many areas and is particularly prevalent in areas such as Bangladesh, West Bengal, and parts of China and the USA. Arsenic contamination of drinking water in Bangladesh and West Bengal has been described as the largest mass poisoning of a population in history, with millions of people affected. Rice is one of the main foods in As-epidemic areas and irrigation with As-contaminated water has resulted in rice with elevated levels of As. The European Food Safety Authority has called for As intake to be reduced. This can only be achieved with a better understanding of the pathways of As uptake and transport within rice plants and this is the aim of the first part of my project. This is a problem of genuine international significance that can only be addressed by an interdisciplinary approach.Wheat grain storage proteins are of immense importance in food processing as they form a viscoelastic network in dough trapping the carbon dioxide bubbles formed during sugar fermentation causing the dough to rise when baked. These proteins are deposited in the starchy endosperm region of the grain, which gives the white flour fraction on milling. However, the starchy endosperm is not a homogenous tissue, with clear gradients in the content and composition of starch, protein and cell wall polysaccharides. These gradients have implications for grain processing as they may allow the production of flour fractions with specific compositions and processing properties. However, they are also of fundamental interest in relation to understanding the control of endosperm development and the synthesis of the gluten proteins which determine the processing properties.This project will use NanoSIMS - state of the art high resolution secondary ion mass spectrometry - to localise As in the nodes of rice plants, the point in the stem where solutes are split into two streams with one controlling uptake to the leaves and one to the rice grain. Several transporters controlling As uptake into the grain have been identified and I will be comparing the distribution of trace amounts of As at the nodes of wild type rice plants with mutants which are missing these specific transporter genes therefore blocking the uptake of As. In the second part of my project I will use the capability of the NanoSIMS to detect isotopes to investigate the distribution of proteins in developing wheat grains. Wheat plants will be fed with compounds used for nitrogen fertilisation which have been isotopically spiked with 15N. The plant is unable to distinguish naturally occurring 14N from 15N, which has a low natural abundance, therefore its distribution in the grain can be used to directly infer mechanisms of protein synthesis. This research will primarily be undertaken at the Department of Materials at Oxford University. This is a highly collaborative project and will involve scientists working in the fields of plant physiology, environmental science, crop nutrition and cereal grain structure and composition to develop new methodologies and improve understanding of the uptake and deposition of key elements in plants. Sample preparation of biological samples for SIMS analysis is difficult and complex. The Life Sciences department at Oxford Brookes University have a lot of expertise in preparing biological materials for TEM and, as we have discovered, NanoSIMS analysis. Samples will be grown at Rothamsted Research, prepared at Oxford Brookes University and the distributions of the key elements will be determined with the NanoSIMS in the Oxford Materials department. The strong collaborative links will be used to interpret these results to make an impact to the scientific knowledge in many aspects of plant science.