Increasing the oil content of plant biomass could help fulfill the nation's increasing demand for renewable energy feedstocks. But many of the details of how plant leaves make and break down oils have remained a mystery. Now a series of detailed genetic studies conducted at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and published in The Plant Cell reveals previously unknown biochemical details about those metabolic pathways including new ways to increase the accumulation of oil in leaves, an abundant source of biomass for fuel production.
Using these methods, the scientists grew experimental Arabidopsis plants whose leaves accumulated 9 percent oil by dry weight, which represents an approximately 150-fold increase in oil content compared to wild type leaves. "This is an unusually high level of oil accumulation for plant vegetative tissue," said Brookhaven Lab biochemist Changcheng Xu, who led the research team. "In crop plants, whose growth time is longer, if the rate of oil accumulation is the same we could get much higher oil content-possibly as high as 40 percent by weight," he said. And when it comes to growing plants for biofuels, packing on the calories is the goal, because energy-dense oils give more "bang per bushel" than less-energy-dense leaf carbohydrates.
Deciphering biochemical pathways:
The key to increasing oil accumulation in these studies was to unravel the details of the biochemical pathways involved in the conversion of carbon into fatty acids, the storage of fatty acids as oil, and the breakdown of oil in leaves. Prior to this research, scientists did not know that these processes were so intimately related.
KEY FINDINGS:
The research revealed that there is no direct pathway for fatty acids to move from the chloroplasts to the peroxisome as had previously been assumed. Instead, many complex reactions occur within the endoplasmic reticulum to first convert the fatty acids through a series of intermediates into plant oils. These oils accumulate in storage droplets within the cytoplasm until another enzyme breaks them down to release the fatty acid building blocks. Yet another enzyme must transport the fatty acids into the peroxisome for the final stages of degradation via oxidation. The amount of oil that accumulates at any one time represents a balance between the pathways of synthesis and degradation.
Using these methods, the scientists grew experimental Arabidopsis plants whose leaves accumulated 9 percent oil by dry weight, which represents an approximately 150-fold increase in oil content compared to wild type leaves. "This is an unusually high level of oil accumulation for plant vegetative tissue," said Brookhaven Lab biochemist Changcheng Xu, who led the research team. "In crop plants, whose growth time is longer, if the rate of oil accumulation is the same we could get much higher oil content-possibly as high as 40 percent by weight," he said. And when it comes to growing plants for biofuels, packing on the calories is the goal, because energy-dense oils give more "bang per bushel" than less-energy-dense leaf carbohydrates.
Deciphering biochemical pathways:
The key to increasing oil accumulation in these studies was to unravel the details of the biochemical pathways involved in the conversion of carbon into fatty acids, the storage of fatty acids as oil, and the breakdown of oil in leaves. Prior to this research, scientists did not know that these processes were so intimately related.
KEY FINDINGS:
The research revealed that there is no direct pathway for fatty acids to move from the chloroplasts to the peroxisome as had previously been assumed. Instead, many complex reactions occur within the endoplasmic reticulum to first convert the fatty acids through a series of intermediates into plant oils. These oils accumulate in storage droplets within the cytoplasm until another enzyme breaks them down to release the fatty acid building blocks. Yet another enzyme must transport the fatty acids into the peroxisome for the final stages of degradation via oxidation. The amount of oil that accumulates at any one time represents a balance between the pathways of synthesis and degradation.
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