Plant-Branching Architectures.

Author:Grifantini, Kristina

IT MIGHT SEEM like a tomato plant and a subway system do not have much in common, but both, it turns out, are networks that strive to make similar tradeoffs between cost and performance. Using 3D laser scans of growing plants, scientists at the Salk Institute for Biological Studies found that the same universal design principles that humans use to engineer networks like subways also guide the shapes of plant-branching architectures. The work, published in Cell Systems, could help direct strategies to increase crop yields or breed plants better adapted to climate change.

"The idea for this work really started with an engineering question," says senior author Saket Navlakha, assistant professor in the Center for Integrative Biology. "How do transportation networks like a subway system or an electric grid resolve the tension between two competing objectives, such as cost and performance--and do plants resolve similar competing objectives in the same way?"

Engineered transportation networks, whether for moving people or power, need to balance the cost of construction with providing efficient transport. Think of a subway system: if the main objective when designing it is to get people from the outskirts to downtown as quickly as possible, each neighborhood will have its own direct line to downtown, but that would be prohibitively expensive to build. Conversely, if the only objective is to limit cost, there would be very few lines, and it would take a long time for some riders to reach downtown. Thus, the engineering challenge is to find some balance of these two objectives. If you extend this analogy to a plant, its base is like downtown and its leaves are like the city outskirts. Nutrients need to get between these areas as quickly as possible, while limiting the cost of growing extraneous branches.

In engineering and other fields, tradeoffs such as this can be represented on a graph as a curved line called the Pareto front. Here, one end of the curve represents a very affordable system that has low performance, while the other end represents an expensive system with high performance. Points along the curve represent different ratios of cost to performance. When applying this framework to plants, the team defined cost as the total length of the branches, because it takes energy and resources for the plant to grow them. They defined performance as the sum of distances from the plant's base to each leaf because this represents how far nutrients...

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