Exploring the influence of the plant lateral root gravitropic set point angle on architecture in soils using X-Ray Computed Tomography.

当我们观察一棵正在生长的植物时，我们观察到的是由叶、茎和花组成的地上组织。但并不明显的是，所有地上部分的生长都完全依赖于隐藏在土壤中的根系。根系负责获取和吸收健康生长所需的水和必需的矿物质，以及将植物固定在土壤中。这些资源对植物的重要性突出表现为需要以昂贵的肥料形式给予农作物额外的水和营养。然而，化肥的供应不是无限的，磷矿石的库存已经出现令人担忧的减少。除此之外，气候变化的威胁可能导致短期和长期干旱问题的增加。世界人口不断增加，导致对粮食安全的日益关注。简而言之，这就提出了一个问题，即未来能否生产出足够的高质量营养食品来养活世界人口。这一需求对现有的农业用地提出了越来越高的要求。为了增加农业产量，必须提高作物生产力。实现这一目标的一个主要目标是提高植物根系在土壤中定植的效率，增加对水分和养分的吸收。这将提供更大的耐旱性，并减少施肥的需要。研究植物根系的一个主要问题是，它们通常隐藏在土壤中。因此，要看到根系，必须去除土壤，从而失去根系的三维组织。因此，植物科学家使用基于透明琼脂的生长培养基在实验室中培养植物，从而使根部易于可视化。然而，该系统并不能准确地模拟自然生长环境，并质疑所获得的结果是否与自然世界真正相关。该项目将开发一种称为X射线计算机断层扫描（CT）的技术，作为一种在土壤中原位可视化根系的方法。这将允许观察三维组织，从而提供一种直接的方法来评估植物根系定植的土壤体积。在南安普顿大学新成立的CT中心内有执行该项目这一方面所需的高科技设备。植物根系由向下生长的主根组成，主根形成侧枝，形成网状结构。最初，这些侧枝远离主根水平生长，然后向下改变它们的生长方向。侧根的初始生长角度（称为向重力设定点角度或GSA）和在向下重新定向其生长之前所达到的长度是根系的3-D结构的关键决定因素，因此是定殖土壤的体积。一些拟南芥突变体，包括rhd 3已被确定显示GSA的改变，表明它是在遗传控制下。将开展工作来识别和表征更多受根部GSA影响的拟南芥突变体。更好地了解影响侧根生长特性的遗传和环境因素，从而更好地了解根系的整体结构，将对未来提高作物生产力具有重要意义。这项研究中获得的技术和结果将适用于并可转移到广泛的不同植物，包括小麦和油菜，这些植物构成了我们饮食的主要部分。

When we look at a growing plant what we observe are the above ground tissues comprised of leaves stems and flowers. What is not immediately obvious is that all of the above ground growth is absolutely dependent on the root system which is hidden in the soil. The root system is responsible for accessing and taking up the water and essential minerals necessary for healthy growth as well as anchoring the plant in the soil. The importance of these resources to the plant is highlighted by the need for agricultural crops to be given additional water and nutrients in the form of costly fertilizers. However, the supplies of fertilizers are not infinite and already there are worrying decreases in the stocks of rock phosphate. Added to this is the threat of climate change which is likely to lead to increased problems with both short term and long term droughts. The world's population is ever increasing leading to growing concerns about food security. Put simply this raises the question of whether enough high quality nutritious food can be produced in the future to feed the world's population. This need is placing increasing demands on the available agricultural land. In order to increase agricultural output it will be necessary to increase crop productivity. A major target to achieve this goal is to improve the efficiency of plants roots to colonise the soil and increase uptake of water and nutrients. This will provide greater drought tolerance and reduce the need for fertilizer application. A major problem in studying plant roots is the fact that they are generally hidden from view within the soil. Thus to see the root system it is necessary to remove the soil and thus lose the 3-dimensional organisation of the root system. Plant scientists have therefore used clear agar based growth media to cultivate plants in the laboratory allowing the roots to be easily visualised. However this system does not accurately mimic the natural growing environment and questions whether the results obtained and really relevant for the natural world. This project will develop a technique known as X-ray Computed Tomography (CT) as a way to visualise the root system in situ in the soil. This will allow the 3-D organisation to be observed giving a direct way to assess the volume of soil colonised by a plant root system. The necessary high-technology equipment necessary to carry out this aspect of the project is available within the newly formed CT center at the University of Southampton. The plant root system is made of a primary root which grows downwards and which forms lateral branches, elaborating the network. Initially these lateral branches grow horizontally away from the primary root before altering their direction of growth downwards. The initial angle of growth (known as the Gravitropic Setpoint Angle or GSA) of the lateral roots and the length achieved before reorienting their growth downwards are key determinants in the 3-D architecture of the root system and hence the volume of colonised soil. A few Arabidopsis mutants including rhd3 have been identified which display alterations in the GSA demonstrating that it is under genetic control. Work will be carried out to identify and characterise further Arabidopsis mutants affected in their root GSA. Gaining a better understanding of the genetic and environmental factors which influence the growth characteristics of the lateral roots and hence the overall architecture of the root system will be invaluable in attempts to improve crop productivity in the future. The techniques and results obtained in this study will be applicable and transferable to a wide range of different plants including those such as wheat and oil seed rape which form a staple part of our diets.