How Does Pollination Work? Pollen Tubes Play A Key Role

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What happens once pollen arrives at the flower? Image by Jon Sullivan

What role does the pollen tube play in pollination, and how does it really work? The Department of Molecular Biology, at Brown University, has illuminated the intriguing process of pollination in new research published today in Current Biology.

From Embryon to Seedling: Inspired Research Produces Results

Decoded Science recently had the opportunity to ask Dr. Johnson about this research. Our first question? We asked Dr. Johnson about the inspiration for this research. He responded,

“We are inspired by the very interesting biology of the pollen tube. This is a very fast growing cell that grows to a precise place and then explodes to release two sperm. One fuses with the egg to make an embryo and eventually the new plant, the other fuses with the central cell to make tissue that supports the embryon and seedling. How does the pollen tube get to its destination? How do the sperm fuse with female gametes once they get there?

“For this project we were curious to try to understand how it is that each ovule receives only one pollen tube. The benefits of this system for flowering plants are really important. The proper number of sperm are delivered – 2. If more are delivered, polyspermy could result (more than one sperm fusing with the egg). This is lethal. If a pollen tube fails to come, that ovule is wasted. We are trying to figure out the molecular mechanisms that create such an efficient system.”

Pollen tubes in lilies: Image by Neutr0nics

Next Steps in Research

The cells that attract pollen tubes continue to do so until gamete fusion has taken place, at which point they stop – We asked Dr. Johnson if he has additional research planned to identify the molecular signal responsible. Dr. Johnson responded, “Yes, we would love to identify the molecules and mechanisms that prevent pollen tubes from targeting an ovule that has already been fertilized. It looks like there may be an active mechanism that repels the late-arriving pollen tubes.”

Improving Seed Yield and Agriculture

This research has a great deal of potential for a number of industries, and may improve commercial fertilization, and agriculture around the world by improving seed yield. According to Dr. Johnson,

Pollen tube growth and gamete fusion are important determiners of seed yield. If we fully understand the basic mechanisms required for these processes we may be able to engineer them to be resistant to environmental conditions that limit seed yield like high temperature. The human diet is based on seeds (grains). So we feel that this basic research that is sponsored by the National Science Foundation could have important future impacts on agriculture.”

Better Fertilization, One Pollen Tube at a Time

Dr. Johnson tells us that the most significant aspects of this research are the specifics of the pollination process.

“We have shown that after one pollen tube arrives at an ovule, it is gamete fusion (when the sperm fuse with the egg and central cell) that triggers a mechanism that prevents more pollen tubes from targeting that same ovule. In cases where defective sperm are delivered, this system allows an ovule to keep attracting pollen tubes until it attracts functional sperm. This system also prevents more than two sperm from being delivered to one ovule. Finally, this system helps to ensure that all ovules get fertilized by distributing pollen tubes to all ovules.”  

Learning more about pollination can have a tremendous impact on not only the agricultural industry, but also improving food production around the world, and advancing research as well.

Resources:

Beale, K., Leydon, A., Johnson, M. Gamete Fusion Is Required to Block Multiple Pollen Tubes from Entering an Arabidopsis Ovule. (2012). Current Biology. Accessed May 17, 2012.

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