Human Frontiers in Science Program Awards $2M CAD to McGill-led International Research Effort

Aeronautical and soft-matter engineering methods may help unfurl an intractable mystery in the biological sciences: how the leaves of land plants are structured to capture carbon and facilitate photosynthetic gas exchange, whilst withstanding gravity and wind.

A team of international research collaborators including McGill’s Professor Anja Geitmann, Canada Research Chair in Biomechanics of Plant Development, has been awarded a prestigious grant in the amount of $2 million CAD from the Human Frontiers in Science Program (HFSP). The project, titled, The Architecture of Photosynthesis is one of nine grants awarded by the HFSP following a rigorous selection process.

Plants use the sun's energy to convert carbon dioxide from the air into material that humans use for food, clothing, construction material, and energy production, and this carbon capture happens primarily in the leaves of plants. Despite the loose tissue arrangement on the inside, leaves must be stable and elastic to withstand gravity, weather, and grazing herbivores. The architecture of the inner tissues of leaves resembles a sponge, allowing for the ambient air to easily flow between the environment and the photosynthetic cells on the inside. While the flat outer shape of most plant leaves is designed for optimal exposure to the sun, orienting towards the sun is a challenge for a thin, sheet-like leaf.

While extensive studies have investigated the architecture of leaves and the strengthening structures that enable them to resist damaging forces, research has neglected to examine the spongy tissue that performs photosynthesis, the mesophyll, which optimizes gas exchange essential for biological carbon capture. Geitmann, in collaboration with Professors John Dear (Imperial College, London) Matteo Pezzulla (Aarhus University), and Craig Brodersen (Yale), aims to fill this enormous knowledge gap.

Despite the associated mechanical challenges, the flat laminar leaf we see today has evolved independently in at least four different plant lineages, suggesting consistent and significant advantages for a sheet-like plant organ in supporting photosynthesis. At the millimeter scale, leaves are a sandwich structure, consisting of stiff epidermal face sheets separated by the softer mesophyll core. Yet how this living tissue develops, maintains its structural integrity, and optimizes the exchange of gases to support photosynthesis is not well understood.

The interdisciplinary research team will investigate how the architecture of plant leaves accomplishes both mechanical stability and optimization for photosynthesis. By understanding how plants arrived at the current laminar leaf form to support photosynthesis, they expect to glean additional insights about how plants can be bred to be more resilient under rapidly changing environmental conditions, and how synthetic materials can mimic their form.

It’s a Balloon…It’s a Plane…It’s a Laminar Plant Leaf!

To shed light on the stability principles of plant leaves and the fundamental evolutionary trade-off governing photosynthesis, the research team will use cutting edge technologies such as deep tissue imaging and biological and engineering methods to analyze the parallels between plant leaf structure and that of airplane wings or ship hulls.

For example, using the engineering principle governing rubber balloons, the researchers will simulate the interactions between individual plant cells in the complex leaf tissues. The behavior of individual cells under load, as well as the role of cell-cell connections and airspaces will be modeled by the Slender Structures Research Group at Aarhus University, led by Matteo Pezzulla. "The mechanics of thin structures such as rubber balloons is deeply rooted in their geometry, leading to models that are usually scale-independent,” said Pezzulla. “This project represents an exciting opportunity to push these ideas even further and pair geometric mechanics and biology to answer long-standing questions."

The sandwich design will be modeled by the Composites, Adhesives and Soft Solids (CASS) Group at Imperial College London, led by Professor John Dear, which has expertise in the mechanical behavior of sandwich structures designed for aeronautical and marine applications. “Our expertise in analyzing mechanical behaviour of sandwich structures designed for aeronautical and marine applications positions us well to model the intricate sandwich design of leaves,” said Dear. “We are excited to collaborate with the HFSP-backed international research team in unravelling the enigmatic design principles of leaf architecture.”

Architectural and geometrical data in 3D (three dimensions) and 4D (3D + time) will be acquired by the Geitmann lab at McGill, led by Professor Anja Geitmann, experts in plant cell biology and imaging. “Bringing engineering into the fold when trying to understand evolution is the type of interdisciplinary and creative research that brings the field forward”, said Geitmann.

Linking mechanics with gas exchange behavior and photosynthesis will be done by the Brodersen lab at Yale University, led by Professor Craig Brodersen. “One of the most exiting parts of this project is that the collaborative, interdisciplinary approach will help us better understand how laminar leaves evolved, and why they’re still the most efficient platform for performing photosynthesis”, said Brodersen. Plants have had ~400 million years of ‘research and development’ solving all kinds of problems while adapting to life on land, and there’s still a lot to learn about these amazing structures.”

Read the release from the HFSP

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