Seed ejection mechanism in an Oxalis species

Shanpeng Li,Jianlin Liu,Yun Zhang

doi:10.1038/s41598-020-65885-2

Shanpeng Li, Jianlin Liu + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-65885-2

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Abstract

With millions of years’ evolution, plants and fungi have developed a variety of ballistic dispersal structures for seeds or spores. One typical example is the catapult of an Oxalis sp., which can realize a consecutive seed ejection by triggering only one seed. If the protrusion on an aril, a specialized outgrowth covering a seed, is disturbed, cracks would occur and cause the opening of the aril. Subsequently, the whole aril snaps and transforms its stored strain energy to eject the inside seed with an optimal launching angle. Once the first seed is triggered, its curly aril will contact the next seed’s protrusion and induce its firing. This chain effect will further trigger the remaining seeds in turns, within 0.1 s. Inspired by this phenomenon, we invented a bionic ejection device to launch projectiles with high efficiency. This exploration is promising for a number of applications, such as drug delivery and oil displacement.

Highlights

Lacking muscles like animals, plants and fungi have evolved various functions to realize the organ deformation in the process of growth and reproduction[1,2,3,4,5,6,7,8]
It should be mentioned that the adjacent catapults of the above-mentioned plants or fungi do not affect each other, i.e. the seeds or spores in one catapult are ejected just by their host catapult. This means that in order to launch the seeds or spores totally, all of the corresponding catapults need to be triggered. Different from these characteristics, we have investigated an Oxalis sp. that possesses a special ballistic dispersal structure to form a consecutive seed ejection, which consumes very little energy by triggering the first seed, similar to a domino show
The fruit of the Oxalis sp. is composed of five valves distributed around a central axis, where each of them contains several seeds in the pericarp, and every seed is covered with an aril as shown in a4 of Fig. 1

Summary

Introduction

Lacking muscles like animals, plants and fungi have evolved various functions to realize the organ deformation in the process of growth and reproduction[1,2,3,4,5,6,7,8]. It can be observed that, due to the existence of partial cracks, the morphology of Impatiens glandulifera seedpod has been exquisitely designed to minimize the energy dissipation[27]. Another way for the far ejection of spore is to reduce the air dragging force; for example, Sphagnum fimbriatum is decorated with vortex rings[16]. It should be mentioned that the adjacent catapults of the above-mentioned plants or fungi do not affect each other, i.e. the seeds or spores in one catapult are ejected just by their host catapult This means that in order to launch the seeds or spores totally, all of the corresponding catapults need to be triggered. The current study is directed towards a comprehensive understanding of the seed ejection mechanism of the Oxalis sp., especially on the energy transformation, optimal launching angle and consecutive ejection

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Conclusion