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

"[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)


"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 BotanyOctober 22, 2016
N. Chaffey

Journal article
Foldable structures and the natural design of pollen grainsProceedings of the National Academy of SciencesOctober 22, 2016
Eleni Katifori, Silas Alben, Enrique Cerda, David R. Nelson, Jacques Dumais