Feasibility of ex planta Lab-grown Wood: A Proof-of-Concept Using Zinnia elegans

By Emma Watts

Introduction

The effects of climate change have escalated the need for novel technologies to manufacture biofuels, construction materials, and consumer goods. Many of these green solutions use plant material as starting products which require land for non-food crops. As the population increases, and as climate changes reduces available arable land, use of non-food crops will become infeasible (1). The potential to grow plant material in the lab would circumvent these issues and provide a useful, practical, and environmentally friendly source of starting materials in various industries. Wood is used for example in furniture production, construction work, and as a feedstock for fuels (2).

Ashley Beckwith, a PhD candidate at the Velásquez-García lab at MIT, has been developing a method to grow plant tissue in the lab, with findings published in the Journal of Cleaner Production in March 2021 (3). Here, the benefits of the method, the experimental design and results, and current limitations will be discussed.

Benefits of ex planta wood

Lab-grown plant material would have several benefits. Growth would be independent of climate and could occur at any location as arable land is not needed (4). This improves flexibility of system design and yield of plant material. The method also eliminates the issue of resource waste, as growing whole plants expends energy to produce superfluous materials such as twigs, roots, and leaves not used in production; here, only wood and secondary xylem are produced (3) . The resources needed to grow the whole plant, such as pesticides and fertilisers would also not be needed. Further, as the parameters of this experiment (hormone levels, pH, media) become better understood, the method will become increasingly adaptable for different design specifications (3). Moreover, not only is the plant material directly produced but it can be shaped into particular moulds through bioprinting and casting (5). So, rather than assembling parts of a coffee table for example, the wood can be grown in one piece using a table mould.

Experiment design and results

The totipotent nature of specific plant cells is exploited in this experiment; small amounts of plant material can regrow the whole plant. Zinnia elegans was used as a model following work in this organism in other studies (6). The production method involved extraction of Zinnia cells from leaves, culture in liquid media for proliferation, and transfer to a gel with the specified hormone and pH parameters (figure 1). Results were then visualised using fluorescence microscopy to measure lignification, elongation and enlargement of the plant cells under various conditions. Cells were grown within nutrient-rich scaffolds to direct growth shape (figure 2).

Beyond the proof-of-concept, this study tested the importance of physical and biochemical parameters such as level of the growth hormones cytokinin and auxin, initial cell density, morphology, and the pH and media for growth. The two hormones were found to interact in dynamic ways to elicit complex results. pH was shown to have an effect only in low-hormone media, where low pH led to improved elongation.

Current drawbacks

As a novel method, production rates are far from suitable for industrial use. Inefficiencies need to be addressed in the cultivation and harvest of plant tissue, and in early processing of the final material (3). The structure of the wood is also not as highly ordered as in nature and lacks directionality (5). Further investigation is needed in the mechanical forces of the gel matrix, the interactions between gel and media constituents, as well as in gas exchange rates and cell-to-cell signalling (3). Only by fully understanding the exact roles of different biological factors in plant growth can this system be fully optimised and scaled for industrial production. Further, the use of artificial light and heat in place of natural land growth raises the energy costs of the method (4). Yet, the lab group are optimistic that this technology will be fit for use in the next decade (5).

Outlook

Proof-of-concept studies such as these demonstrate the important role of biotechnological methods to combat the increasing risk to industrial production in response to climate change. Creative and collaborative solutions will be required to manage production with limited resources, with interdisciplinary approaches becoming increasingly important. This study paves the way for future work in optimising the design process and extending into the use of other plant species.

References

1 – Foley, J.A., Ramankutty, N., Brauman, K.A., Cassidy, E.S., Gerber, J.S., Johnston, M., Mueller, N.D., O’Connell, C., Ray, D.K., West, P.C., Balzer, C., Bennett, E.M., Carpenter, S.R., Hill, J., Monfreda, C., Polasky, S., Rockström, J., Sheehan, J., Siebert, S., Tilman, D., and Zaks, D.P.M. (2011) ‘Solutions for a Cultivated Planet’. Nature 478 (7369), 337–342

2 – Hurmekoski, E., Jonsson, R., Korhonen, J., Jänis, J., Mäkinen, M., Leskinen, P., and Hetemäki, L. (2018) ‘Diversification of the Forest Industries: Role of New Wood-Based Products’. Canadian Journal of Forest Research 48 (12), 1417–1432

3 – Beckwith, A.L., Borenstein, J.T., and Velásquez-García, L.F. (2021) ‘Tunable Plant-Based Materials via in Vitro Cell Culture Using a Zinnia Elegans Model’. Journal of Cleaner Production 288, 125571

4 – Ackerman, D. (2021) ‘Could Lab-Grown Plant Tissue Ease the Environmental Toll of Logging and Agriculture?’ MIT News 20 January

5 –  Berry, K. (2021) ‘Lab-Grown Wood Could Be Future of Furniture’. BBC News 4 March

6 – Fukuda, H. and Komamine, A. (1980) ‘Establishment of an Experimental System for the Study of Tracheary Element Differentiation from Single Cells Isolated from the Mesophyll of Zinnia Elegans’. Plant Physiology 65 (1), 57–60

Images:

Figure 1: Workflow of Plant Material Development (1)

A small sample from Zinnia elegans is grown either by maceration to isolate plant cells or via callus culture to obtain totipotent plant cells. From there, cells are grown in varying suspension cultures to promote growth and test the various growth parameters, and a cast or scaffold is used to direct growth for a desired form.

Figure 2: Bioprinted culture (1)

Macroscopic substrate visualisation of plant cells. The cells have grown within the scaffold to produce a 3D-bioprint. This has been visualised using a Zeiss LSM780 confocal microscope which detects natural autofluorescence of lignin at 355/488 nm and 455/535 nm).

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