Double-cropping isn't a new idea in agriculture, but producing plastic in plants as a value-added commodity would give new meaning to the concept for Missouri farmers, said a University of Missouri researcher.
Since 2000, Brian Mooney, an MU research assistant professor of biochemistry, has worked to enhance a system of agricultural plastic production that would create new market opportunities for commodities such as corn and soybeans while reducing plastic in landfills and dependence on foreign oil.
“Each year, 25 million tons of plastic end up in U.S. landfills,” he said. “If we can replace some petroleum-based plastics with those made from a non-polluting, renewable resource such as plants, we can reduce that number and create new income for farmers.”
The plastic Mooney is attempting to produce is polyhydroxybutyrate-valerate, or PHBV, which is similar to the petroleum-based plastic, polypropylene.
“PHBV is flexible and moldable, and could be used to produce a wide range of products, from grocery bags and soda bottles to disposable razors and flatware,” he said. “The advantage of PHBV is that it's 100 percent biodegradable. When discarded, bacteria that naturally occur in the soil chew it up and turn it into water and carbon dioxide.”
In the mid-1990s, Monsanto Corporation successfully produced PHBV in plants, which the company called BIOPOL, Mooney said. “But they were only able to produce it in small quantities, about 3 percent dry weight. In order to be commercially viable, 14 percent or more is considered the threshold.”
Mooney seeks to break this threshold by designing plants that produce the raw materials for PHBV within leaf cells.
“There are five enzymes, two from the plant and three from bacteria, that when combined produce PHBV,” he said. “Of the two plant enzymes, one is currently produced in the mitochondria. Our goal is to modify the plant so that this enzyme is instead diverted to the chloroplasts. Once that's achieved, bacterial enzymes can be introduced to produce PHBV in the chloroplasts.”
Laboratory experiments show the mitochondrial enzyme can be diverted to the chloroplasts, Mooney said. The next step is to use the model plant, Arabidopsis, to confirm the system works in plants.
“We anticipate the first plants will be produced in the next six to 12 months,” Mooney said. “At that point, we'll analyze the expression of the enzymes, and if they're sufficient, we'll be ready to move on to the next step.”
For farmers, PHBV could become an additional agricultural commodity, creating a double crop in one plant, he said. “Whether in corn or soybeans, the plants would be designed to produce the PHBV plastic in the leaves only, leaving the seed unchanged. Monsanto studies from the 1990s showed that PHBV-producing plants grew normally and produced fertile seed.”