Making Plastics (and Other Fine Things) from Plants

One of the major problems facing the developed world is the need to find renewable substitutes for declining stores of coal and oil, which supply energy and the raw materials for plastics, nylons, and other industrial products. Another major problem is to develop more healthful foods, ones that are broadly available and reasonably priced. In the past few years, Arabidopsis researchers have made several discoveries that should go a long way to meeting both of these challenges.

An important first step in designing better foods was made a few years ago when Chris Somerville and coworkers, then at Michigan State University in East Lansing and now at the Carnegie Institution of Washington at Stanford, California, found and cloned the Arabidopsis desaturase gene which codes for an enzyme that catalyzes the synthesis of polyunsaturated fatty acids. Dietary polyunsaturated acids have a role in lowering blood cholesterol and are needed for normal human growth.

Since the discovery of this gene in l992, scientists working with Somerville, including John Browse at Washington State University in Pullman and others at DuPont in Wilmington, Delaware, and at Monsanto in St. Louis, have isolated most of the eight different desaturase genes from Arabidopsis that control the polyunsaturation of plant oils. Plant breeders have then used these Arabidopsis genes to isolate the corresponding genes from crop species. What's more, they put copies of these genes into some plants, such as soybeans, canola, and flax, that typically make more saturated oils. This resulted in the production of nutritionally improved oils in these crops. These genetically transformed plants were field tested in the fall of l994, only 2 years after the key discoveries were made. "This gives an indication of how quickly industry can move to apply basic research," says Somerville. "We think we can tailor plant oils to specific nutritional needs." Somerville adds that "Most of the work that led up to this came from basic studies of Arabidopsis."

Related research focuses on developing custom-designed plants that will reduce our reliance on nonrenewable sources of petrochemicals, which are needed to make plastics and related materials. The goal is to modify plants genetically so that instead of producing edible oils, the plants will produce industrial oils and polymers, which are now made from petroleum stocks.

Somerville and his colleagues have shown that it is possible to genetically engineer Arabidopsis to produce granules of polyhydroxybutyrate (PHB), a polyester used for biodegradable plastic containers which is usually obtained from a bacterium, Alcaligenes eutrophus. The researchers did this by taking two genes the bacterium uses to make PHB and putting them into Arabidopsis. At first, the genetically transformed plants produced only minute granules of this valuable plastic. However, after a few years of tinkering, researchers inserted modified genetic constructs into the plants and could increase production enough to attract considerable commercial interest.

No one is suggesting that tiny Arabidopsis plants be developed as a commercial crop for plastics production, but whatever is learned from the Arabidopsis model can be used with other, more practical, crops, such as canola or soybean. Ganesh Kishore of Monsanto in St. Louis, which is one of several major companies studying the commercial possibilities of this system, says, "Our goal is to produce biodegradable plastic from a renewable source. We will create a whole new paradigm for the plastics industry."

Somerville adds that the production of plastics in plants will have the added benefit of giving farmers new markets for their harvests. "American agriculture produces too much of too few products. And novel plant varieties, created with the aid of Arabidopsis genes, will give farmers new cash crops," he says. What's more, he suggests that plastics are just the beginning, and that croplands of genetically transformed plants may be devoted to the production of, for example, hydraulic oils, lubricants, nylons, drugs, and valuable enzymes.

Analysis and Recommendations for the Coming Year