Gifts from Christmas trees

With Christmas just around the corner, gifts and presents are being wrapped and put under small pine trees across much of the world. But pine trees themselves also have many gifts to give, not only as a biofuel feedstock but also as a producer of resin. Pine trees naturally produce this sticky substance as a form of self-defense when wounded or infected. This is because resin comprises a mixture of toxic terpene compounds such as pinene, carene and limonene that can kill microbial pathogens and insect pests.

In the past, these terpene compounds also proved useful for the production of a wide range of products, including paint, varnish, shoe polish and linoleum, but then lost out to crude oil as a chemical feedstock. With crude oil now losing favor, attention is reverting back to the terpene compounds in resin, but with the difference that scientists are looking to derive an even greater range of products from them.

For example, scientists at the Fraunhofer Institute for Interfacial Engineering and Biotechnology in Stuttgart, Germany, have developed a one-pot method for converting the pinene, carene and limonene in pine resin into lactams, essential building blocks in the production of polyamides. They have thus found a biological route to producing this widely used plastic that doesn’t required food crops as a feedstock.

What is more, their process results in the production of an amorphous, rather than crystalline, version of polyamide. “Our biobased polymers are predominantly ‘amorphous’ and thus transparent, which is very unusual for biobased polyamides,” says Harald Strittmatter, who heads the project. This means the bio-based polyamide can be used for producing things like visors and ski goggles.

Strittmatter and his team are now experimenting with combining the resin-derived lactams with other monomers to produce co-polymers with a greater range of properties, and are also working on transferring their one-pot production method to a pilot plant.

These efforts should be boosted by recent research conducted by Mark Lange and his colleagues at Washington State University in the US. Using various genetic and microscopy techniques, they investigated in detail how resin is produced by loblolly pine trees (Pinus taeda). This resin is stored in resin ducts found in the bark, and Lange and his colleagues confirmed that the majority of the resin is also synthesized in epithelial cells in these ducts, rather than in the mesophyll cells in pine needles.

As the scientists report in a paper in the Journal of Experimental Botany, they were also able to identify many of the genes that take part in resin synthesis, and thus piece together some of the metabolic pathways. These pathways appear to involve the simple sugars produced by photosynthesis in the mesophyll cells being subjected to oxidative phosphorylation and fermentation in the epithelial cells.

"We are trying to understand the biochemical reactions that lead from a simple imported carbon source to a complex mixture of oleoresin and products," said Lange. "That's the factory."

With this information, scientists may be able to boost production in the factory, which will be required if the resin from pine trees is to become a major chemical feedstock, and modify it to produce other complex chemicals. They could also potentially boost production by transferring the terpene-synthesizing metabolic pathways into microbes such as yeast or Escherichia coli that are already used for industrial production in bioreactors. Whatever happens, this research at least confirms that pine trees aren’t just for Christmas.

The views represented here are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. or of the SCI.