What is it about?

Desiccation of pollen grains induces their infolding, but a special mechanical design of the grains is required in order for them to close regularly and fully. The paper examines the role of the elastic inhomogeneity of the pollen grains in infolding, in particular the shape, softness and the number of the soft regions in the pollen wall called apertures. It is shown that the pollen with larger number of apertures requires a more precise tuning of the elastic parameters in order to close regularly (the grains with smaller number of apertures close more robustly), although it has the advantage of germinating with larger probability. The high abundance of grains with three apertures may possibly be an evolutionary compromise between these two opposing requirements.

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Why is it important?

Although the diversity of pollen grains is huge, our study is an attempt to to determine certain mechanical characteristics which may be common to a large number of species. Such a comparison and distillation should also shed some light on the evolution of pollen. The results could also be important for the design of inhomogeneous elastic shells which respond with a programmed deformation to the changes in their surrounding. Such shells could perhaps be used for the encapsulation of (microscopic) matter and drug delivery. In contrast to homogeneous shells which resist external pressure all up to the point of catastrophic failure, the inhomogeneous shells can be designed to respond continuously and to deform in a desired manner, depending on the pattern of elastic inhomogeneity - the soft regions can effectively guide the infolding of such shells.


We have worked earlier on physics of viruses, in particular on mechanical and electrical features of their design which enable them to remain reasonably stable in the extracellular space, but also to readily disassemble once they get in the cellular surrounding. Although the pollen grains are thousand times larger, the requirement of mechanical efficacy and its evolutionary traces are quite similar.

Antonio Šiber
Institute of Physics, Zagreb

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This page is a summary of: Mechanical design of apertures and the infolding of pollen grain, Proceedings of the National Academy of Sciences, October 2020, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2011084117.
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