Native Village 
Youth and Education News

March 1, 2013

Can plants be altruistic? You bet, says new CU-Boulder-led study
Condensed by Native Village


Unselfishly concerned for or devoted to the welfare of others.

A study led by the University of Colorado Boulder suggests some plants are altruistic.

The researchers looked at corn, in which each fertilized seed contained two “siblings.” The siblings are an embryo and a corresponding bit of tissue called endosperm, which feeds the embryo as the seed grows.

They compared growth and behavior of embryos and endosperm in seeds sharing the same mother and father, vs those that had genetically different parents.

The results?

"...embryos with the same mother and father as the endosperm in their seed weighed significantly more than embryos with the same mother but a different father,” said Professor Pamela Diggle from CU-Boulder. “...endosperm that does not share the same father as the embryo does not hand over as much food. It appears to be acting less cooperatively.”

Their findings were published in the Proceedings of the National Academy of Sciences. Co-authors included Chi-Chih Wu, a CU-Boulder doctoral student, and Professor William  Friedman, a professor at Harvard University.

Previous research indicated that plants may prefer to withhold nutrients from inferior offspring when resources are limited.  “Our study is the first to specifically test the idea of cooperation among siblings in plants,” Diggle said.

“One of the most fundamental laws of nature is that if you are going to be an altruist, give it up to your closest relatives,” said Friedman. “Altruism only evolves if the benefactor is a close relative of the beneficiary. When the endosperm gives all of its food to the embryo and then dies, it doesn’t get more altruistic than that.”

When corn reproduces, male flowers at the top of the plants distribute pollen grains two at a time.
The pollen travels down through tubes to tiny cobs on the stalks covered by strands known as silks. This process is known as double fertilization.
When the two pollen grains touch an individual silk, they produce a seed containing an embryo and endosperm.
Each embryo results in just a single kernel of corn..

Wu cultivated the corn and harvested more than 100 ears over a three-year period. He removed, mapped and weighed every individual kernel out of each cob from the harvests. Most kernels had an endosperm and embryo of the same color. That indicates they shared the same mother and father. Less than 1% had different colors, such as a purple outer kernel with yellow embryo. This meant they had two different fathers.

Wu was searching for those rare 1% as a way to assess cooperation between the embryo and endosperm.

“It was very challenging and time-consuming research,” said Friedman. “It was like looking for a needle in a haystack, or in this case, a kernel in a silo.”

Endosperm -- in the form of corn, rice, wheat and other crops -- is critical to humans. They provide about 70% of calories we consume annually worldwide.

“The tissue in the seeds of flowering plants is what feeds the world,” said Friedman.  “If flowering plants weren’t here, humans wouldn’t be here.”

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