Packing plants with eco energy
Super energy-rich biofuels could soon be possible because of new research, dramatically reducing the environmental impact of intensive farming.
Researchers in the US have grown plants with 170 times more oil in their leaves content compared to normal plants, significantly boosting the amount of energy that can be packed into them. Currently, plant oils are largely extracted from seeds, leaving much more abundant green vegetation to go to waste.
Should field trials prove successful, the work could increase the nutritional value of plant products, increase electricity production from biomass, and make farming more efficient.
The work could also have important implications on the production of environmentally-destructive oil products such as palm oil, which has led to deforestation of large swathes of tropical rainforest, threatening species such as the orang-utan.
"Palm oil is a major source for producing biodiesel," said Dr Changcheng Xu, at Brookhaven National Laboratory, who led the research. "If we can make the stem or leaf store oil to produce biodiesel or bioelectricity then we will use much less acreage."
Xu's team worked with the model plant species Arabidopsis thaliana -- also known as thale cress -- a common plant species in laboratories around the world.They found that genetically manipulating the plants to make an excess of an enzyme called PDAT resulted in oil-rich leaves.
"PDAT catalyses the last step of oil biosynthesis", said Xu. "If you overexpress PDAT, you can make this step much more efficient."
Increased PDAT levels also stimulated the production of a precursor to oil formation, a small fat chemical known as a fatty acid.
"One stone: two birds," joked Xu.
Unfortunately, this type of manipulation was not stable, because the oil droplets that formed were quickly broken down by other enzymes in the plant cells.
However, by simultaneously increasing the amount of a protein called oleosin, which maintains oil droplets in seeds, the leaves not only produced stable excess oil, but also accumulated up to 170 times the normal amount.
Work must next take the technology outside of the lab, but several hurdles must be overcome before the work will transform the agricultural landscape.
One such hurdle is that excess oil production diverted important fats away from chloroplasts, the solar cells that convert sunlight to sugar.
Xu explained that the problem may vary by plant, as different species build chloroplasts in different ways.
"In plants like spinach, PDAT over-expression won't turn the plants pale green," explained Xu. "But in other [high biomass] plants, there may be a problem."
Collaborations within the laboratory are now working to apply the technique to sugarcane and switchgrass. Green vegetation of oil-rich sugarcane, for example, could be burnt to generate bio-electricity. Very little of the crop would therefore be wasted, as the same harvest could be used to generate electricity and produce sugar and bio-ethanol products.