February 1st, 2013 by James Ayre
Plants can demonstrate altruistic behavior, a new study from the University of Colorado Boulder has found.
Evidence of altruism, and clear social behavior and communication, has previously been observed in plants. Plants have previously been found to aggressively compete with some genetic strangers, cooperate with others, and to team up with close relatives. This new research builds upon that to provide strong evidence of altruism in plants from the get go, right after the seed is fertilized.
For the new study, researchers focused on corn, “in which each fertilized seed contained two ‘siblings’ — an embryo and a corresponding bit of tissue known as endosperm that feeds the embryo as the seed grows. They compared the growth and behavior of the embryos and endosperm in seeds sharing the same mother and father with the growth and behavior of embryos and endosperm that had genetically different parents.”
“The results indicated 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 Pamela Diggle, a faculty member in CU-Boulder’s ecology and evolutionary biology department. “We found that 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.”
As the researchers note, previous research has shown that plants “can preferentially 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.”
“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 Professor William 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.”
During corn reproduction, pollen is distributed by male flowers at the top of the plants “two at a time through individual tubes to tiny cobs on the stalks covered by strands known as silks in a process known as double fertilization. When the two pollen grains come in contact with an individual silk, they produce a seed containing an embryo and endosperm. Each embryo results in just a single kernel of corn.”
“The researchers took advantage of an extremely rare phenomenon in plants called ‘hetero-fertilization,’ in which two different fathers sire individual corn kernels. The manipulation of corn plant genes that has been going on for millennia — resulting in the production of multicolored ‘Indian corn’ cobs of various colors like red, purple, blue and yellow — helped the researchers in assessing the parentage of the kernels.”
Over a three year period, more than one-hundred ears of corn were grown, harvested, and then had every single kernel removed, sorted and weighed. The vast majority of the kernels were formed from an endosperm and embryo of the same color, but some of them very multicolored, featuring a different color outer kernel than the embryo.
By using the multi colored kernels, the researchers were then able to compare the degree of cooperation between the embryo and endosperm.
“Endosperm — in the form of corn, rice, wheat and other crops — is critical to humans, providing about 70 percent of calories we consume annually worldwide. The tissue in the seeds of flowering plants is what feeds the world,” said Friedman, who also directs the Arnold Arboretum at Harvard.
The new research was just published January 21st in the journal the Proceedings of the National Academy of Sciences.
Image Credits: CU-Boulder; Corn via Wikimedia Commons
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