Pollen of flowering plants can survive extreme dehydration via several mechanisms, including a reversible wall-folding pathway that results in complete impermeability.

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“[O]ne of [pollen’s] great mysteries is how it can withstand desiccation. Even though the near-spherical shape of some species’ generates surface-area-to-volume ratios that minimise water loss, and their walls are surrounded by an impermeable outer later of exine, this is interrupted by apertures that provide exit routes for ‘materials’. And, as dry as pollen grains can be, loss of too much water will result in their death. So, it is intriguing to know how they manage to stay hydrated. Well, according to Elena Katifori et al. (PNAS 107: 7635–7639, 2010) it’s all down to ‘simple geometry’ and a phenomenon called harmomegathy. Although Katifori and colleagues did not invent the term, they do demonstrate that geometrical and mechanical principles explain how the wall structure guides pollen grains toward distinct folding pathways. During harmomegathy the pollen surface undergoes a folding process to produce a sealed pollen grain in which those permeable apertures become neatly tucked inside the impermeable exine.” (Chaffey 2010:vi)

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References

“Upon release from the anther, pollen grains of angiosperm flowers are
exposed to a dry environment and dehydrate. To survive
this process, pollen grains possess a variety of
physiological and structural adaptations. Perhaps the most striking of
these
adaptations is the ability of the pollen wall to
fold onto itself to prevent further desiccation. Roger P. Wodehouse
coined
the term harmomegathy for this folding process in
recognition of the critical role it plays in the survival of the pollen
grain. There is still, however, no quantitative
theory that explains how the structure of the pollen wall contributes to
harmomegathy.
Here we demonstrate that simple geometrical and
mechanical principles explain how wall structure guides pollen grains
toward
distinct folding pathways. We found that the
presence of axially elongated apertures of high compliance is critical
for achieving
a predictable and reversible folding pattern.
Moreover, the intricate sculpturing of the wall assists pollen closure
by preventing
mirror buckling of the surface. These results
constitute quantitative structure-function relationships for pollen
harmomegathy
and provide a framework to elucidate the functional
significance of the very diverse pollen morphologies observed in
angiosperms.” (Katifori et al. 2010:7635)

Journal article
Plant CuttingsAnnals of BotanyFebruary 23, 2011
N. Chaffey

Journal article
Foldable structures and the natural design of pollen grainsProceedings of the National Academy of SciencesApril 20, 2010
Eleni Katifori, Silas Alben, Enrique Cerda, David R. Nelson, Jacques Dumais

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Living System/s

Organism
PlantsPlantaeKingdom

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