According to a new study published in the journal Cell, plants favor the production of uneven, asymmetrical patterns on the surface of pollen grains over more symmetrical patterns.
Pollen patterns: SEM images and simulations. Image credit: Asja Radja / Maxim Lavrentovich.
“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,” said Dr. Maxim Lavrentovich, from the University of Tennessee, Knoxville.
“However, the function of the precise pattern on this surface is not well understood.”
Biologists observed that in approximately 10% 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,” Dr. Lavrentovich said.
“The separation of oil from water in a bowl of soup is a good example of this.”
“In this case, what gets separated is a low-density mixture of polysaccharides from a high-density one.”
In contrast, the other 90% of living plant species either never reach the equilibrium point and produce asymmetrical pollen grains, or achieve smooth, un-patterned grains.
This predominance shows that Nature does not favor a point of equilibrium in most plant seeds during their evolution process.
For the study, Dr. Lavrentovich and co-authors 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,” Dr. Lavrentovich said.
“In the future, we would like to refine our model by better characterizing both the physical and chemical parameters of the phase separation process.”
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Asja Radja et al. Pollen Cell Wall Patterns Form from Modulated Phases. Cell, published online February 7, 2019; doi: 10.1016/j.cell.2019.01.014
