Biophysics of Plant Defence: From Rose Prickles to Sugar Transport

Sabrina Gennis, PhD Student at Department of Physics, Technical University of Denmark (DTU)

You are likely familiar with the pleasant smell of a basil plant, the hazardous prickles of a rose, or the curious leaf movements of a Mimosa pudica plant in response to touch, but did you know these are all examples of plant defence strategies? Additionally, many defences remain hidden, such as chemical signalling or the occlusion of flow within the plant’s sugar transport system. Since plants have had hundreds of millions of years to evolve, there is much we can learn from them, and biological systems often outperform artificial ones. Therefore, gaining a better understanding of plants’ defence mechanisms is essential not only to shed light on systems within plants but also to design and improve applications inspired by nature.

Here, some defence mechanisms have been studied in greater detail: rose prickles and occlusion of the sugar transport system.

Plant defence mechanisms can include sharp outgrowths such as prickles on a rose or spines on a cactus. Interestingly, most defensive stingers in nature are more or less circular in cross-sectional aspect ratio. However, the base of a rose prickle is elliptical. Experiments with model prickles of different aspect ratios suggest that the shape might be evolutionarily beneficial for cutting and climbing. The optimal aspect ratio could be used to engineer improved gripping tools.

A plant's survival is not just dependent on its ability to defend itself, but also on the successful transport of sugars. However, sugar transport can be impaired by occlusion during a defence mechanism. A trade-off between occlusion and flow was identified, leading to an optimal conduit geometry. The geometry of various plants seems to follow this best geometry. In the future, comparisons of flow or size across different plants should be conducted with caution.