Lignin in leatherwood: the key to replacing petroleum based plastic?

For the past several decades, forestry has been interested in developing transgenics to improve wood production. This is because in the majority of vascular plants, lignin biomass averages 20-30%, which means there is a large energetic and monetary cost to remove this unwanted lignin, a hydrophobic molecule with strong covalent bonds, during processing (Robinson, 1990). But despite its cost to paper and pulp mills, lignin has exciting potential applications as an organic molecule in the pharmaceutical, construction, and packaging fields, among others (Albuquerque et al., 2021). With proper bioengineering, lignin could even be used as a biomaterial capable of replacing fossil fuels in plastic production. However, current research and knowledge of lignification, the process wherein lignin is deposited in the plant, is lacking when it comes to our ability to produce widely-commercially viable plants with manipulated lignin properties. This is where the small, bendy shrub, Eastern leatherwood, enters the picture.

Eastern leatherwood. Image by Tom Potterfield

During the course of my four months with the Fagerstedt lab, I had the opportunity to work with leatherwood, a species that was recently discovered to have unique lignin patterning, in a completely novel way (Mottiar et al., 2020). While I knew that I would likely use antibody staining to identify the locations of molecules, such as pectin, I didn’t know that I would have the opportunity to use a transmission electron microscope, or to turn this research into a thesis project.

One of the best things about science, and this traineeship with HiLIFE, is that I was able to try things that I, nor anyone else, had ever done before. With Yaseen’s expertise, the post-doc supervising me, I went from researching how to use a transmission electron microscope, which sends a particle beam through your ultra thin sample, allowing you to see where electrons are able to pass through, and where they are blocked, to actually embedding samples in small, pill-shaped resin capsules and eventually imaging those samples on a machine that looks like a spaceship (the transmission electron microscope). This type of microscopy allowed us to see, in extremely fine detail, the cell wall of leatherwood tissue. While the image below has some sample flaws (the dark line is a wrinkle in the wood section, and a few of the cell walls have torn), I think it’s a really cool way to see the cambium (with inner cellular contents that have been destroyed) and the empty xylem cells that, in a living tree, would transport water. Below is a sample of leatherwood, and if you look at the area between the cell walls, or middle lamella, you can see that it’s lighter in color, indicating that there is not staining present, and therefore there is not enough lignin present to darken the area.

TEM image of leatherwood sample stained with potassium permanganate.

I’m so grateful for the opportunity to spend four months of full-time work trying out different wet lab techniques and learning about what it is like to be a full time researcher. Additionally, this research has provided a step further in the quest to generate transgenic trees with modified lignin content and distribution. Hopefully in the future, scientists will be able to modify commercial species with lignin in ways that allow lignin to be used to replace plastics, among other things.


Works cited

Albuquerque, B. R., Heleno, S. A., Oliveira, M. B. P. P., Barros, L., & Ferreira, I. C. F. R. (2021). Phenolic compounds: Current industrial applications, limitations and future challenges. Food & Function, 12(1), 14–29.

Mottiar, Y., Gierlinger, N., Jeremic, D., Master, E. R., & Mansfield, S. D. (2020). Atypical lignification in eastern leatherwood (Dirca palustris). New Phytologist, 226(3), 704–713.

Robinson, J. M. (1990). Lignin, land plants, and fungi: Biological evolution affecting Phanerozoic oxygen balance. Geology, 18(7), 607–610.<0607:LLPAFB>2.3.CO;2

Studying an unusual shrub (Eastern leatherwood) and the beginning of my HiLIFE grant

Lignin and its chemical properties are, for the most part, fully taken advantage of in most plant and tree species: it’s a molecule that occurs in the area between neighboring cells, inside the cell wall, and generally provides mechanical support and supports water transport. But this looks a little different in leatherwood, a small, understory shrub that lacks lignin in places where there are normally large amounts in other species, such as silver birch or Norway spruce. This allows its branches to bend well past what would easily break a spruce tree. Interestingly, we still do not understand why leatherwood evolved like this (other than the fact that being extremely bendy is obviously a fun skill).

Lignin, in this sense, can be thought of as one of the many Bermuda triangles of the plant world. While much of plant biology remains unknown, lignin is particularly interesting because how and why lignin is distributed, especially in leatherwood, remains a mystery.

My name is Dayla and, while I’m originally from Austin, Texas in the United States, I have lived in California, West Virginia, New York City, and now Helsinki. One of the reasons that I was drawn to the University of Helsinki is because of the access to plant science research, ranging from stomatal development to lignin formation.

Before entering the master’s program here, I was already considering whether a PhD in plant biology could be the right path for me, but I was scared. Was this really what I wanted? A decade of mass-murdering weeds for the sake of science?

The short answer, I think, is yes. The slightly longer answer is that I have been lucky enough to work with HiLIFE to spend four months exploring lignin and its many roles in leatherwood, poplar and Norway spruce. Over the course of this traineeship, I will have the opportunity to see how trees fit into the wider world of plant biology, learn new techniques (including how to pick up 20 micron thick pieces of wood using only a drop of water), and explore the possibility of a career in research.

In the past, I’ve worked with Arabidopsis roots to investigate genes responsible for growth and development. Now, with Kurt Fagerstedt’s group, I will have the opportunity to study a different facet of plant biology – what happens to a plant when one of its key macromolecules is modified.

However, the real main goal of this traineeship is to resolve the love–hate relationship that I have with lab refrigerators. They smell similar to how it feels to gag – that is to say, I gag every time I open one. Alas, this is where we store the true muscle of developing mutant plants, and the culprit of the smell: E. coli. This bacteria is partially responsible for the transformation of healthy, strong weeds, into sad, small plants that are no longer able to produce lignin properly.

Over the course of the next four months, I hope that I can either a) grow accustomed to the smell in the refrigerator or b) appreciate the importance of E. coli in plant molecular biology enough that it no longer bothers me.