Researchers discover new type of lignin in vanilla, cactus

NEWS RELEASE
Issued - January 23, 2012

ARDMORE, Okla. — Collaborators at The Samuel Roberts Noble Foundation, Rutgers University and the University of Wisconsin have discovered a new type of lignin that holds the potential to be a new source of carbon fibers for manufacturing.

The discovery, which has been supported by the Department of Energy's BioEnergy Sciences Center and Great Lakes Bioenergy Center, has received widespread attention in the scientific community, including selection as the cover story for the upcoming issue of Proceedings of the National Academy of Sciences, where the research is published, and an "editor's choice" story in an upcoming volume of Science magazine - two of the world's most cited multidisciplinary scientific journals.

"Discoveries such as this open doors to new areas of research and application," said Rick Dixon, D.Phil., director of the Noble Foundation's Plant Biology Division. "This is a significant breakthrough in plant science research which drastically changes our view of lignification, yet at the same time we're just beginning to understand how we can utilize this new information."

Lignin is a compound present in all plants that helps strengthen cell walls, providing structure and support - basically giving the plant the ability to stand upright. Lignin can theoretically be made from five components (so-called monolignols, represented by the letters H, C, G, 5-OH-G and S). The majority of lignin is a combination of G and S units with low levels of H units. 5-OH-G is only seen in genetically modified plants, and C units are essentially unreported.

In 2011, Dr. Daphna Havkin-Frenkel, Ph.D., Rutgers University, a vanilla expert and a collaborator on previous work at the Noble Foundation, asked Dixon's lab to help with analysis of lignin in vanilla beans. As a recognized leader in lignin research, the Noble Foundation often receives requests for such analyses. However, during this analysis of vanilla lignin, Noble research scientist Fang Chen, Ph.D., spotted what appeared to be a low level of the unexpected C component.

Knowing that this could be a mistaken identification, Chen decided to separate the seeds and the pods of the vanilla bean and test them separately. The pod contained no C component, whereas the black seeds of vanilla contained all C units. "A plant part containing all C-lignin has never been seen before," Dixon said. "This is like the gem that falls into your lap."

This was the "white whale" of lignin research, said collaborator John Ralph, Ph.D., Professor of Biochemistry at the University of Wisconsin and a world expert on lignin structure determination. Ralph and his postdoctoral fellow, Yuki Tobimatsu, Ph.D., determined the detailed chemical structure and size of the vanilla C-lignin, confirming this was a novel polymer made only of C-units. Ralph and Tobimatsu also used nuclear magnetic resonance analysis to discover that the polymer was remarkably uniform with a linear structure.

Since vanilla is in the orchid family, the discovery sparked a search for C-lignin in other orchids provided by Havkin-Frenkel, but C-lignin was only found in vanilla species. Noble Foundation researchers then began looking in other plant families closely related to orchids, such as asparagus and agave - but still no C-lignin.

In the summer of 2011, Chen had an occasion to observe black seeds protruding from pods on top of a Melocactus, a type of cactus common to the Caribbean and South America. The cactus was not the object of research at the Noble Foundation but rather was part of Dixon's personal collection. Chen sought to evaluate the seed, which looked rather like vanilla seed, for C-lignin.

"He was thinking that if C-lignin happened to be in one black seed, why could it not be in another?" Dixon said. "Lo and behold, there was C-lignin again. So now, this C-lignin has been discovered in dicots (cactus) and monocots (vanilla), two groups of plants that are separated by a huge evolutionary distance."

The researchers evaluated the lignin composition of many other cactus species seed. The new C-lignin appeared in some, but not all, of the species within a specific genus, or family, of cactus. Seeds either contained all C-lignin, or normal G/S lignin, but never both. "This suggests to us that formation of C-lignin occurs by a relatively simple mechanism," Dixon said. "Lignin plays a role in protecting and coating the seed, and it seems that plants are still evolving the ability to make this new lignin."

After Ralph's team determined the linear nature and uniform structure of the C-lignin chemical polymer, samples of this lignin were sent for analysis by the Oak Ridge National Laboratory to evaluate its role in the potential manufacture of useful consumer products, like carbon fibers or plastics. Carbon fibers continue to be an important research avenue because of their high tensile strength and light weight. "Often in science you come up with a fabulous idea and spend two years proving it wrong," Dixon said. "This discovery is an example of something simple coming out of the blue and quickly turning into something of great scientific and, potentially, technological interest."

The next step will be to learn how this new lignin is made, such that it can be produced in greater scale, or quantity, where its value can be fully realized. The research was funded in part by two of the Department of Energy's research centers devoted to the development of biofuels: the BioEnergy Sciences Center (BESC) at Oak Ridge, Tenn., and the Great Lakes Bioenergy Research Center (GLBRC), Madison, Wis.

"Discoveries, such as the new C-lignin, are a great example of how researchers collaborating and sharing ideas through resources such as BESC and GLBRC can have significant outcomes that push the boundaries of our understanding," said Paul Gilna, Ph.D., Director of BESC. "C-lignin has application to our bioenergy missions as well as to specific industries, such as agriculture and carbon fiber research, and it will be exciting to see what other benefits this discovery will reveal in the coming years."

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For media inquiries concerning the Noble Foundation, please contact:

J. Adam Calaway

jacalaway@noble.org

The Samuel Roberts Noble Foundation, Inc. (www.noble.org), headquartered in Ardmore, Okla., is a nonprofit organization conducting agricultural, forage improvement and plant biology research; assisting farmers and ranchers through educational and consultative agricultural programs; and providing grants to nonprofit charitable, educational and health organizations.