Peanuts. Photo curtesy of Microsoft clip art.


The most important interaction the peanut, as well as all legumes, have is between themselvesThe molecular geometry of atmospheric nitrogen. Notice the triple bond between the two nitrogens. This is what makes it so hard to separate. Picture created by Veronica Steinmetz. and the rhizobial bacteria that inhabit their roots. These bacteria, from the genus Bradyrhizobium, take on the job of nitrogen fixation (scroll down link to "Nitrogen Fixation") for the plant. A supply of nitrogen is vital to plantThe molecular geometry of ammonia. It is a much more usable form of nitrogen. Picture created by Veronica Steinmetz. life and a lack of it often inhibits plant growth. Unfortunately, the nitrogen available from the atmosphere (N2) is an unusable form due to the extremely strong triple bond between the two nitrogen atoms. So, to solve that problem, legumes have formed a mutualistic relationship with the rhizobia. The rhizobia are provided with a safe place to live and carbohydrates for energy while the peanut receives usable nitrogen, generally ammonia (NH3). It is this way of getting nitrogen that allows the peanut to live poor quality soil with no problem.

A photo of some nodules growing on the roots of a broad bean. Photo courtesy of Wikimedia Commons.The peanut's rhizobia live in pockets of plant material that grow from the roots called nodules. But the rhizobia don't just automatically start there. When the peanut plant is still young, the rhizobia move towards the peanut's roots, there is a moment of mutual recognition between the rhizobia and plant, and then the rhizobia begin to colonize on the root surface. Once the rhizobia have attached themselves, they enter the root by one of three ways. Which way it happens is determined by the peanut plant. Typically, they can either enter through the root hairs, which is the most common way, through an injury, or between undamaged epidermal cells. In the peanut, the rhizobia send a signal that cause the hairs at the emerging lateral roots to deform. This causes the structure of the cell walls to be altered, thus allowing the rhizobia to enter. Once inside, the rhizobial bacteria begin to quickly multiply, and the cells that hold the rhizobia repeatedly divide to create the nodule. Soon, the peanut root possesses its own personal nitrogen fixing knob.

Want to learn some more about other legumes with these rhizobia? Check out these pages:Cartoon of an open peanut shell. Picture courtesy of Microsoft clip art.
Cartoon of a peanut. Picture courtesy of Microsoft clip art.Garden Pea
Velvet Bean
Pongam Tree

Although the peanut does have a wonderful relationship with a bacteria that provides life-giving nitrogen, it is by no means the perfect plant. It may not have toPicture of a mature peanut pod infected with Thanatephorus cucumeris. Photo courtesy of Wikimedia Commons. deal with shortages of nitrogen, but it does have its problems. These problems arise in the form of pests such as the Heliothis species of moth, which can cause a lot of damage in large numbers, and the fungus Thanatephorus cucumeris, which causes "damping off" of seeds, which means to stop them from growing. Also, virtually all peanut butter in the United States contains some amount of alfatoxin, a fungal toxin that is a known carcinogen, which means it is known to cause cancer. But don't worry! The Food and Drug Administration (FDA) has regulations in place that make the amount of aflatoxin in peanut butter far below fatal, or even noticable, levels. 

There is also another organism that the peanut plant has important interactions with. That organism is, of course, humans! As an important food crop and all around versatile plant, most people do have at least some sort of contact with peanuts or peanut products. To learn more about the uses of peanuts, please click on the link below.


What can you use it for? And wasn't George Washington Carver involved somehow?

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