Inhibition of Carbon Assimilation by excess Radiation: Understanding maize weak Spot (ICARUS)

对植物来说，光既是一种资源，也是一种潜在的压力因素。光合作用利用来自太阳的能量将二氧化碳固定为糖和构成生命的蛋白质，然而，叶片通常接收的光是通过光合作用处理的光的5倍。为了避免受到太多光照的伤害，植物进化出了一系列保护自己的方法。然而，由于其他树叶的遮挡、云的掠过和阳光方向的改变，光照水平是高度动态的。因此，植物需要能够非常迅速地进行调整。过度保护会导致光合作用和生长的丧失，而保护不足则会使叶片容易受到损害。理论预测表明，保护水平的更快变化可能有利于增长和生产力。事实上，我最近证明，当保护水平的变化加快时，这将显著提高模式作物在田间条件下的光合作用效率和生产力。理论分析表明，玉米可以从提高对强光的保护和加快恢复速度中受益更多，但我们缺乏了解，无法确定需要改进的具体目标。玉米是全球最主要的农作物，全球产量为10.9亿吨。玉米在温带地区的种植越来越多，在英国，玉米是一种受欢迎的动物饲料作物，也是用于厌氧消化器提供生物能源的作物，2017年总生产面积为195.000公顷。有趣的是，玉米似乎很难保护自己免受太多光照的伤害。光造成的伤害严重限制了玉米的产量，特别是在早季的晴朗凉爽的日子里，植物往往看起来黄色和矮小，但在非常炎热或干燥的条件下也是如此。提高玉米的保护水平和调整率预计将使生产率提高高达30%，并具有巨大的经济价值，特别是对英国等温带气候的农业来说。玉米对光敏感和缓慢调节的原因尚不清楚。玉米光合作用利用生化泵将光合作用的底物二氧化碳浓缩到特化的束鞘细胞中。这种所谓的C4途径提高了光合作用的效率，但也使光合作用的局限性比传统光合作用的植物更难研究。在光系统水平上，我们不知道哪种光合作用复合体最脆弱，在细胞水平上，我们不知道这两种光合作用细胞中哪一种最容易受到抑制。因此，该项目的目的是利用一种新的非侵入性测量技术组合来识别导致玉米光合作用易受光抑制影响的弱点。拟议的研究计划将集中在：1)哪些特定的光合作用电子传递蛋白是玉米光抑制的主要瓶颈2)哪种光合作用细胞类型最受光抑制影响2)哪种光条件最有可能引起光抑制3)玉米抵御过多光的能力是否不足这一结果将提供详细的了解玉米光合作用中响应过多光的薄弱环节，并将被综合为玉米光合作用和作物改良的优先列表。

Light is both a resource and a potent stress factor for plants. Photosynthesis harnesses energy from the sun to fix carbon dioxide into sugars and the protein building blocks of life, However, leaves routinely receive up to 5 times more light than can be processed via photosynthesis. To avoid damage by too much light, plants have evolved a range of ways to protect themselves. However, light levels are highly dynamic due to shading by other leaves, clouds passing over and changing direction of sunlight. As a result, plants need to be able to adjust very rapidly. Over-protection leads to a loss of photosynthesis and growth, whereas under-protection renders the leaves susceptible to getting damaged. Theoretical predictions indicated that more rapid changes in protection levels might benefit growth and productivity. Indeed, I recently demonstrated that when changes in protection levels are accelerated, this dramatically improves photosynthetic efficiency and productivity under field conditions in a model crop. Theoretical analysis suggests that maize could benefit even more from improving protection against high light and accelerate recovery rates, but we lack understanding to pin-point the specific targets that need improving. Maize is the most dominant crop globally, with a world-wide production volume of 1.09 billion metric tons. Maize is increasingly being grown in temperate regions and in the UK is a popular crop for animal fodder and for use in anaerobic digesters to provide bioenergy, with a total production area of 195.000 ha in 2017. Intriguingly, maize seems to have a difficult time protecting itself against too much light. Light-inflicted damage strongly limits productivity of maize, especially during bright cool days in early season, when plants can often look yellow and stunted, but also under very hot or dry conditions. Improving the protection level and adjustment rate in maize is predicted to improve productivity by up to 30%, and would hold great economic value, especially for agriculture in temperate climates such as the UK. The reasons for the sensitivity to damage by light and slow adjustment in maize are unclear. Maize photosynthesis utilizes a biochemical pump to concentrate carbon dioxide, the substrate for photosynthesis, in specialized bundle sheath cells. This so-called C4 pathway increases the efficiency of photosynthesis, but also makes photosynthetic limitations more difficult to study than in plants with conventional photosynthesis. At the photosystem level, we don't know which photosynthetic complex is most vulnerable, and at the cellular level, we don't know which of the two photosynthetic cell types is most easily inhibited. The aim of this project is therefore to identify the weaknesses in maize photosynthesis leading to its vulnerability to photoinhibition, using a novel combination of non-invasive measurement techniques. The proposed research programme will focus on: 1) which specific photosynthetic electron transport proteins are the main bottlenecks underlying maize photoinhibition 2) which photosynthetic cell type is most impacted by photoinhibition 2) which light conditions are most likely to give rise to photoinhibition 3) whether the capacity of maize to protect against too much light is insufficientThe results will provide detailed understanding of the weak links in maize photosynthesis in response to too much light and will be synthesized into a priority list of improvements in maize photosynthesis and crop improvement.