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

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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.