Researchers have genetically engineered the leaves and stems of tobacco plants so that the plants produce twice the normal amount of oil, making tobacco a more viable energy crop candidate.
Up to 40 percent of a dry tobacco seed’s weight is oil, which can be chemically combined with an alcohol to produce biodiesel, or used in a more complicated process to produce a different renewable fuel that is very similar to conventional diesel, called renewable diesel. But since it produces very few seeds compared to traditional energy crops like soybeans and canola, conventional tobacco isn’t considered a realistic biofuel source.
The genes responsible for seed oil production also exist in tobacco’s leaves and stems, or biomass — they just aren’t switched on. So Vyacheslav Andrianov and Nikolai Borisjuk, plant geneticists at Thomas Jefferson University in Philadelphia, used two established genetic engineering techniques to artificially activate these genes in the plant’s biomass, thereby increasing oil production. “There is this molecular machinery there, so our idea was to use it to channel the production of oil into the biomass,” Borisjuk said.
The group chose tobacco because it offers important advantages. First of all, Borisjuk said, tobacco is a well-studied plant, and it is “pretty easy to metabolically transform” its oil production properties. Second, compared to other plants, tobacco produces an abundance of leaves and stems. “The idea was to combine these two features, oil production and large production of biomass,” he said. The research was funded by the State of Pennsylvania’s Alternative Fuels Incentive Grant Program.
In a paper published in December 2009 in the journal Plant Biotechnology, the research team reports a two-fold increase in the accumulation of fatty acids, the major component of vegetable oils, in the biomass. They also report up to a 20-fold increase in the accumulation of triacylglycerol, a molecule the biofuel industry desires because it can be converted directly into biodiesel.
Now the researchers plan to continue to refine their method and hope to further increase biomass oil accumulation. Tobacco, however, is years away from being an industrial-scale energy plant. There remain technological barriers to actually getting the oil out of green plant tissue. “It’s easy to get oil from seeds, but it’s a lot harder to get oil from green tissue, and the amount they can extract is limited right now,” said Joanne Morello, a conversion technologist in the U.S. Department of Energy’s biomass program.
Still, Morello said, this result is a proof of concept. If an environmentally friendly chemical extraction process can be developed, tobacco could have a promising future as a biofuel plant, especially since it offers so much biomass and is not a food crop. In the past, using food crops, such as corn, for energy production purposes has caused spikes in food prices due to increased demand.
Another advantage to the plant is that the farming infrastructure for growing tobacco already exists. Since the demand for cigarettes has dropped off significantly, much of the land that had been used for growing tobacco has been taken out of service, making it available for reintroducing the once reliable cash crop.
In addition to oil production, tobacco biomass could also be useful in making next-generation ethanol from cellulose, the fibrous compound that is the major structural component of plants. Switchgrass is the most publicized feedstock for cellulosic ethanol, but some tobacco strains would also fit the bill because they are high in sugars and low in lignin, a wood-derived chemical that hinders a plant’s usefulness in ethanol production. Tobacco “is the type of plant where, after the oil is extracted, you could give the residual biomass to yeast to ferment into ethanol,” Morello said.
Many other plants are also attractive for energy purposes, said study author Andrianov, so this research is useful even if it only serves as a model for how to turn other crops besides tobacco into energy plants. But the potential economic benefits of reinstating tobacco as a cash crop, given the existing infrastructure and agricultural know-how, are especially motivating, he said. “Tobacco growers will be very happy if we can achieve this.”