description
- Most of what we know about photosynthesis comes from studying leaves. However, other plant non-foliar organs (e.g. stems, flowers and fruit) are also known to photosynthesize. The wheat spike is the flower of the wheat plant. While the leaf is often assumed to be the sole-source of carbohydrates for grain production, recent results have shown spike photosynthesis contributes up to 40% to grain weight. However, unlike leaves, how spike photosynthesis responds to its environment is largely unknown. At the top of the canopy, the spike is exposed to the extremes of heat and light. High temperatures - the result of heatwaves brought about by global warming - damage key photosynthetic processes that reduce the duration of spike carbon capture from the air, leading to severe decreases in yield. I have developed a custom imaging screen which has uncovered diversity in leaf-level photosynthetic heat tolerance, suggesting that untapped variation may also reside in the spike photosynthetic tissues. To date, no methodology exists for rapidly screening wheat spikes for heat tolerance traits. This proposal will address the lack of fundamental knowledge surrounding spike heat tolerance and its complex role in maintaining wheat grain yields under extreme temperatures. This proposal takes a top-down approach to addressing the gaps in our knowledge of spike responses to heat. First, the development of novel methodology to rapidly identify variation in spike heat tolerance will facilitate efficient assessment of the diversity available in current wheat varieties. Comparing this spike heat tolerance dataset with the genetic background of these varieties allows us to identify any associations between variation in this trait and key genetic variations or 'markers' present on the wheat genome. The identification of these genetic markers is of immediate benefit to the wheat research community; from researchers interested in the genetic regulation of spike heat tolerance to wheat breeders selecting heat tolerant wheat varieties to include in breeding programs. After identification of heat tolerance, this proposal focuses on the fundamental, mechanistic processes that promote spike cooling in the field. Despite its clear importance, very little is known about the physical interaction of the spike with its environment. As the spike matures, its shape changes and so will the spikes' interaction with its environment; not only impacting on the delivery of vital carbon dioxide for photosynthesis but also how efficiently heat is transferred away from the essential photosynthetic processes. This project proposes using state-of-the-art imaging techniques to model the flow of air around the spike to determine how changing spike shape regulates heat, while balancing the delivery of carbon. This fundamental, exploratory study underpins future work into assessment of spike gas exchange - enabling researchers to investigate non-foliar structures with the same depth of understanding as leaves. Finally, the techniques developed here will be applied to the spikes of the closely related wild relatives of modern wheat. Representing a relatively untapped source of genetic diversity, introducing these species into modern wheat has already uncovered several, leaf-level improvements including disease resistance. Investigating wheat wild relative spikes for heat tolerance introduces another potential trait for inclusion into breeding programs but also represents an ecological aspect of this work which can be explored in the future. As a BBSRC Discovery Fellow, I will pioneer exploration of heat tolerance in non-foliar organs by initially focusing on the wheat spike. Quantifying and understanding variation in this currently unexplored trait is vital, providing a source of heat tolerance which will not only improve our understanding of non-foliar photosynthesis but also contribute to national and international food security as climate change accelerates.