The development of a novel herbicide

点击翻译按钮获取中文摘要

In the next 50 years the global population is expected to increase by 50% and exceed 9 billion. The increased agricultural output needed to feed this growing population cannot be met by bringing more land into food production as no further suitable arable land is available. Therefore, meeting this challenge will require the adoption of highly efficient and sustainable agriculture practices. Efficient agriculture requires the removal of weeds. Current arable farming relies on ploughing to remove weeds by burying them as the soil is turned over. However, ploughing (tillage) removes vegetation cover, disrupts the soil structure and leads to soil erosion by water, wind or both. The Dust Bowl inter-war era in the mid-western United States graphically illustrated the vulnerability of plough-based agriculture as wind blew away precious topsoil from the drought ravaged southern plains whose soil structure had been weakened by ploughing. No-till farming is a branch of conservation agriculture in which the ground is permanently covered by a cover-crop that is left on the fields over winter to protect the soil. The roots of the cover crop hold the soil particles together, strengthening the structure and foliage intercepts rain water to lessen its impact on the soil. In this method of farming, herbicides, rather than the plough, are used for weed control and, prior to planting, the cover crop is degraded by the application of a broad spectrum herbicide and the dead organic matter is left on the surface to degrade naturally. Seeds are then drilled into the ground through the residue in a process that results in minimal disturbance of the soil and improved water retention. A further benefit of no-till is that the cover crop acts as a carbon sink removing CO2 from the atmosphere during photosynthesis with the non-harvested residue being converted to soil organic matter. It has been estimated that approximately half of the overall potential for U.S. croplands to sequester soil carbon comes from conservation tillage. Moreover, as no-till is less mechanised, agricultural diesel use is reduced by 50-80%. No-till therefore offers the potential to off-set fossil fuel emissions in other sectors. It has been suggested that the global introduction of no-till could result in the annual sequestration of 1 billion tons of carbon, 15% of that required to limit atmospheric CO2 to a trajectory that avoids further increases over today's levels. This saving is equivalent to that saved from the global doubling of nuclear capacity replacing coal, or to the combined annual emissions of all the road transport currently in use on the planet. Whilst the benefits of no-till in decreasing soil erosion and promoting carbon capture are clear, its practice relies on the availability of effective herbicides. More importantly, in order to avoid damage to the emerging crop, the herbicide has to have the property of being inactivated when it contacts the soil so that available residues are minimised. However, reliance on compounds that act by inhibiting a limited number of processes in plants has encouraged the emergence of herbicide resistant weeds. Sustainable agriculture therefore requires the development of herbicides having novel modes of action. The search to find new herbicides is now an important area of research. In this project we aim to examine the prospect of developing a new herbicide, that will be targeted against an enzyme, called imidazoleglycerol-phosphate dehydratase, which is responsible for a key step in the synthesis of histidine, an amino acid that is essential for plant growth. We will determine the atomic structures of a number of chemicals that bind to this enzyme, and use this information in a process of design, to chemically synthesize new compounds that will both inhibit the enzyme activity and be inactivated on soil contact. These new compounds will thus kill the weeds in a new way and facilitate sustainable agriculture practices.