Plants As Plants: Gene Could Convert Crops To Plastics Factories

Clint Chapple, professor of biochemistry at Purdue University, and Knut Meyer of DuPont and Co., have cloned a gene from the common laboratory plant Arabadopsis that will allow materials to produce plastics in crops without damaging the plant's health.

A patent application, in which both Purdue and DuPont have rights, has been filed on the use of the gene for the production of monomers. Chapple also received the 2001 Agricultural Researcher Award from the Purdue School of Agriculture for his work.

Currently, petroleum is used to make nearly all plastics; it also is used as a base material or solvent in paints, household and industrial chemicals and in thousands of other applications.

But crop plants such as corn or soybeans hold the potential to create plants that provide the starting materials to make the plastics we already have and to make new plastics with never-before-seen properties, Chapple says.

Plastics are produced by making chains of compounds derived from petroleum. Scientists call these chains polymers, and the individual molecules that form the chain are called monomers.

One reason scientists are interested in making plastics from plants is that plants produce an amazing array of compounds that could be used for monomers in plastics.

“We have been historically limited by the number of polymers that we can make from petroleum,” Chapple says.

Plants also are much more versatile than petroleum.

“Plants are really amazing chemical factories that produce a mind-boggling number of interesting chemicals," Chapple says. "We can exploit that ability by using genomics to identify the genes required to make those compounds and by using biotechnology to insert the genes into crop plants.”

Until now, however, the problem has been trying to get plants to make enough of these substances for the whole process to be economically viable, he says. “Although crude oil supplies are finite, petroleum has been a much less expensive source for plastic monomers.”

Fortunately, plants already have methods for making and storing large amounts of compounds that help protect them from insects, disease and ultraviolet radiation in sunlight. They do this by combining (or to use the scientists’ preferred term, conjugating) the molecules with other molecules to produce stable, soluble forms of the compound that are stored in small structures, called vacuoles, within the cells. The vacuoles isolate the compound from the rest of the biochemical processes going on in the plant.

“We’ve now cloned a gene that produces an enzyme that is in involved in conjugating these compounds in plants,” Chapple says.

The project is part of DuPont’s “Plants as Plants” initiative. “DuPont is interested in making new plastics and other products from crop plants," Chapple says. "But if you do that you have to make sure that they can be stored in the vacuole in a safe way at a high concentration.”

Meyer says DuPont can be thought of as a company that produces polymers and is constantly looking for new monomers to build new plastics.

“DuPont produces nylon and many related products,” he says. “But some monomers are difficult to make from petroleum using traditional chemistry, so we’re looking at monomers produced in higher levels in plants. Dr. Chapple’s work helps us stabilize these monomers in plants and produce them at higher levels.”

Meyer says DuPont is investigating using genetically modified microbes as well as plants to produce monomers. For example, DuPont has a project near completion that uses the bacterium E. coli to produce the monomer for a type of plastic that is used in carpet fibers, among other things.

However, plants are more attractive chemical factories than microbes because they may be cheaper.

“The inherent advantage with plants is that you get your nutrients for free — the carbon dioxide and sunlight are there for the plants,” Meyer says. “With microbes, on the other hand, you have a high capital investment because you have to build factories to produce and feed them.”

Because plants produce such a wide variety of natural products, Chapple says new products that aren’t even being currently considered might soon be possible.

“Let’s think a bit more creatively,” Chapple says. “In the future, we may still use polyethylene to make some plastics. But we may be able to develop plastics with such special properties that we find new uses for them. Maybe it’s exactly the right compound to use in synthetic heart valves or in parts for jet aircraft, for example. It’s very exciting to think about what may be possible with this research.”

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Related Web sites:

Purdue genomics backgrounder website:http://persephone.agcom.purdue.edu/AgCom/news/backgrd/genomics_home.htm

Chapple's professional homepage: http://www.biochem.purdue.edu/chapple.htm

Dupont: http://www.dupont.com