Pollen Survives Extreme Dehydration

macro of a red flower stamen covered in golden pollen

Biological Strategy

Plants

AskNature Team

Image: Timothy Dykes / Unsplash / Free non-commercial use

Protect From Loss of Liquids

Water is essential to life. Liquids, mostly water, make up 70 to 90% of all living systems, and the loss of even a small percentage can mean the difference between life and death. Living systems must maintain a proper liquid balance, which is especially difficult in dry conditions. To do so, they must control the movement of liquids across their boundaries. Living systems do this using structures or waterproof materials to prevent or slow liquid movement. For example, when humans receive a cut, they must limit blood loss. Scattered throughout the bloodstream are lens-shaped structures that serve to plug the wound.

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Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

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Plants

Phylum Plantae (“plants”): Angiosperms, gymnosperms, green algae, and more

Plants have evolved by using special structures within their cells to harness energy directly from sunlight. There are currently over 350,000 known species of plants which include angiosperms (flowering trees and plants), gymnosperms (conifers, Gingkos, and others), ferns, hornworts, liverworts, mosses, and green algae. While most get energy through the process of photosynthesis, some are partially carnivores, feeding on the bodies of insects, and others are plant parasites, feeding entirely off of other plants. Plants reproduce through fruits, seeds, spores, and even asexually. They evolved around 500 million years ago and can now be found on every continent worldwide.

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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)