What is Biology Good For?
Bio-Plastics: Growing Plastic From Plants

(This assignment is optional and is due on Friday, February 14, 2003 by noon. Read this essay and answer the questions at the bottom for 3 extra credit points. It is not necessary to visit the links in the text unless you are interested in more information.)

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Imagine 340 pounds of solid lineman coming at you at a rate of 5 miles per hour. The actual force on your body is equivalent to a hit from a ton bricks! That's a regular occurrence for professional football players. As football fans gear up for this season, very few consider how players can tolerate these bone-crushing blows only to jump up and get back in the game. They can do this with the help of equipment innovations made possible by plastic.
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Plastics have helped to shape the world around us. They are incorporated into everything from heart valves to baby bottles and are virtually indestructible. However the same feature that makes plastics so versatile, also presents a major concern. One of the most pressing environmental problems in industrialized nations is that of the constantly growing mountain of waste. Conventional plastics are made from oil and do not degrade easily thus contributing to the growing trash heaps across the world. These issues have led scientists to search for alternative sources of plastic that are biodegradable and do not consume the limited resource of petroleum.


Bioplastics produced in genetically modified plants could assist in alleviating the burden on the environment that conventional plastics cause. Much in the same way as animals use fat as an energy store, certain bacteria use substances similar to plastics. Polymers such as PHBV are produced naturally by some species of bacteria and it turns out that PHBV can be heat-formed into a flexible plastic suitable for many applications where biodegradable plastics are desirable, such as packaging. [Image]

PHBV and other such bacterial polymers are fully biodegradable, having been designed by nature as storage products that can be broken down and used as sources of carbon and energy. They also have the advantage that, unlike petroleum-based plastics, they are made from renewable resources. However scientists have found that trying to produce PHBV from bacteria is uneconomical for large-scale operations. That is why researchers have been attempting to genetically engineer plants to act as mini plastic factories.

With the aid of modern molecular tools, three bacterial genes have been identified as enabling bacteria to manufacture the plastic polymer. An additional gene was eventually revealed to code for the ability to sequester polymers specifically in plastids. Armed with the genes to code for the making and storing of the plastic polymer, the scientists used gene-splicing (genetic engineering) techniques to insert these codes into the DNA of a member of the Mustard family. Some scientists hope that eventually this technology will lead to fields of plastic plants, originating from the Mustard family. [Image]

The Basics of Gene Splicing

The following is a diagram of how the gene splicing technology works.
Recombinant bacteria and plasmid isolation. [Image](From Stern, Introductory Plant Biology, 8th ed., © 2000, McGraw-Hill Companies.)
Using this gene splicing technology, researchers have been able to introduce the engineered DNA (from step B) into a plant instead of a bacterium (step C). Thus allowing the plants to act as mini plastic factories.

The Dark Side of Bioplastics: There are drawbacks to plastic plants, however. The plant-produced plastics are harvested in a series of chloroform extractions in which the plant material is separated from the plastic polymer. It is estimated that plastic extracted from the bacteria would cost $4 per pound, while plant-extracted plastic would cost about $1.50 per pound. But this is still more, however, than petroleum-based plastic, which costs about $0.50 per pound. There is still a long way to go, however, before grow-your-own plastic becomes a reality. The Monsanto team estimates that polymer concentrations need to be around 15% of the plants’ dry weight to make its extraction and processing economic, while in their plants concentrations are less than 3%. Much more research will be needed, and there will be no quick returns.

References

Grow Your Own Plastic, American Plastics Council, Scientists Unveil Plastic Plants, Plastic-Producing Plants: The Cash Crop of the Future, Plastic Plants

This Good For was written and researched by IUPUI Graduate Student Christi Braun, who, when she is not busy studying, is a defensive tackle for the Indianapolis Colts, testing helmets made from Bio-Plastic. Just kidding.

The text of this "What is Biology Good For" exercise is copyrighted under the name of Dr. Kathleen A. Marrs, 1999, 2000, 2001, 2003. There are no restrictions on its use by educators or by non-profit institutions as long as its content not modified, proper copyright acknowledgement is retained, and this statement is not removed.

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