Nature prefers asymmetrical pollen grains, study finds

February 12, 2019

It's no secret that pollen plays a vital role in plant reproduction worldwide, including the production of food. But for decades, scientists have been puzzled about the variety of patterns on the surface of these pollen grains--specifically, how they are formed and if they have a function.

A study published in Cell sheds some light on the subject, showing that plants favor the production of uneven, asymmetrical patterns on the surface of pollen grains over more symmetrical patterns.

"The pollen wall itself--the surface of a pollen grain--serves the important function of protecting the pollen grain genetic material from the environment as the pollen travels during the process of pollination. However, the function of the precise pattern on this surface is not well understood," said Maxim Lavrentovich, assistant professor of theoretical biophysics in the Department of Physics and Astronomy at the University of Tennessee, Knoxville, and coauthor of the study.

Researchers observed that in approximately 10 percent of living plant species the formation of symmetrical, identical, and reproducible pollen grains occurs when the phase separation of pollen production reaches a point of equilibrium.

"A phase separation is the process by which an initially mixed system equilibrates into two or more distinct materials. The separation of oil from water in a bowl of soup is a good example of this," said Lavrentovich. "In this case, what gets separated is a low-density mixture of polysaccharides from a high-density one."

In contrast, the other 90 percent of living plant species either never reach the equilibrium point and produce asymmetrical pollen grains, or achieve smooth, un-patterned grains.

This predominance shows, according to Lavrentovich, that nature does not favor a point of equilibrium in most plant seeds during their evolution process.

For the study, researchers distilled biological features of the pollen pattern development and used that information to construct a physical model of these essential features.

The evolutionary analysis shows that natural selection does not favor symmetrical, uniform pollen patterns, but rather that plants more rapidly develop more disordered, asymmetrical patterns. These disordered patterns are captured in the biophysical model through a kinetic arrest of the pattern evolution.

"We used a simple biophysical model to explain the biological process of pattern creation," said Lavrentovich. "In the future, we would like to refine our model by better characterizing both the physical and chemical parameters of the phase separation process."

The findings provide a better understanding of the pattern-forming process of pollen grains. In a more practical setting, they could help in future efforts to produce artificial pollen.

"Many plant species undergo the pollination process successfully with symmetrically or asymmetrically patterned pollen grains. Still, understanding if these differences have some kind of impact is important for applications such as constructing new patterned materials using a pollen-like physical mechanism and for the categorization of plant species," said Lavrentovich.
The paper, "Pollen Cell Wall Patterns Form from Modulated Phases," was written in collaboration with researchers Asja Radja, Eric M. Horsley, and Alison Sweeney, all from the Department of Physics and Astronomy at the University of Pennsylvania.

CONTACT: Andrea Schneibel (, 865-974-3993)

University of Tennessee at Knoxville

Related Natural Selection Articles from Brightsurf:

Genetic determinants of fertility and ongoing natural selection in humans
A recent study presented at the ASHG 2020 Virtual Meeting suggests genetic variants may be associated with reproductive success.

Forearm artery reveals humans evolving from changes in natural selection
Humans haven't developed genetic mutations for telepathy or superpowers just yet, but a new study shows our species is still evolving in unique ways and changes in the natural selection could be the major reason.

Novel technology for the selection of single photosynthetic cells
New research, published in the journal Science Advances, demonstrates how microfluidic technologies can be used to identify, isolate and propagate specific single photosynthetically active cells for fundamental industry applications and improved ecosystem understanding.

Genomic selection in dairy cows creates opportunities not possible with traditional selection
The 2019 ADSA Annual Meeting featured the Joint ADSA/Interbull Breeding and Genetics Symposia titled ''Ten Years of Genomic Selection'' and ''Data Pipelines for Implementation of Genomic Evaluation of Novel Traits.'' Because of genomic selection's importance to dairy science, the Journal of Dairy Science invited the speakers to submit articles and share information from these symposia with a wider audience.

Recurrent genomic selection for wheat grain fructans
Development of Climate-Resilient, Nutritionally Improved Wheat

NASA's OSIRIS-REx in the midst of site selection
After a lengthy and challenging process, the team is finally ready to down-select from the four candidate sites to a primary and backup site.

The argument for sexual selection in bacteria
The evolutionary pressure to pass on DNA can produce behavior that otherwise makes no sense in a struggle to survive.

Sexual selection influences the evolution of lamprey pheromones
In 'Intra- and Interspecific Variation in Production of Bile Acids that Act As Sex Pheromones in Lampreys,' published in Physiological and Biochemical Zoology, Tyler J.

Infection biology: Signs of selection in the stomach
Helicobacter pylori, a globally distributed gastric bacterium, is genetically highly adaptable.

Study finds natural selection favors cheaters
Natural selection predicts that mutualisms -- interactions between members of different species that benefit both parties -- should fall apart.

Read More: Natural Selection News and Natural Selection Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to