Plants Are Talking; Are You Listening?
Have you ever been walking through the countryside and thought “I wonder what the trees would say if they could talk”? I certainly have; would they tell us about things they have seen in years gone by? Would they ask us what we see as we move from place to place? We as humans are curious by nature and crave connection in the same way as we crave nutrition (Tomova et.al., 2020 Pre-print). From a nod of the head to gushing conversations we communicate constantly, even when it is difficult, people find a way to connect. We are not alone in this – quietly, without our knowing, plants communicate constantly, and we are only just starting to understand how.
The concept for inter-plant communication in itself is not new; Baldwin and Schultz (1983) noted that the chemical profile of damage tissues in Poplars was mirrored in unharmed plants in their vicinity. Their findings lead to the initial discoveries of the actions of volatile organic compounds (VOCs, compounds that easily become vapours or gasses) in plant communication both above and below ground (Massalha et.al., 2017). Furthermore, plants are able to communicate by releasing compounds from their roots into their surroundings (Semchenko et.al., 2014). There is even compelling evidence that underground fungal networks can be utilised by plants to aid in the transport of these root borne compounds to interested parties as a kind of underground phone network (Song et.al., 2010; Gilbert and Johnson 2017). But who are these interested parties? And what exactly are plants talking about?
One of my personal favourite examples is when grasses scream. Now, that sounds a little morbid, but hear me out! I love the smell of freshly cut grass, it is sweet but clean and always makes me think of summer. This smell is made up of a number of chemicals most notably green leaf volatiles, some of those VOCs I mentioned earlier. These chemicals are released in different amounts and ratios depending on how the stress the plant is receiving, such as infection or cutting (Scala et.al., 2013) and it is these green leaf volatiles we are smelling when grass is cut. Both the producing plants and other plants in its vicinity perceive these molecules and defend themselves against the perceived incoming threat (Schwachtje et.al., 2006; Sugimoto et.al., 2014).
It isn’t only ourselves and other plants which recognize these volatiles; insects are also capable of divining information about a plant and it’s position through these chemicals. Many insects communicate with plants through these signals, certain species of Orchid can attract pollinators by mimicking their sex pheromones (Boham et.al, 2018), and insect damaged plants have been shown to attract the predators of their attackers in an act of personal defence (Allmann and Baldwin, 2010; Allmann et.al., 2013). Furthermore, certain pathogenic algae are repelled from newly wounded sights on Poplar roots by the release of these volatile chemicals to defend against secondary infection (Lackus et.al., 2018).
We have only just scratched the surface of plant communication, there are many more types of chemical compounds involved. There are a huge number of other organisms they can communicate with, even accepting messages from bacteria. There is a whole world of chatter we are not privy to, but there you have it – plants are trying to talk to us, we just haven’t learnt how to listen yet.
References
Tomova, L., Wang, K., Thompson, T., Matthews, G., Takahashi, A., Tye, K. and Saxe, R., 2020. The need to connect: Acute social isolation causes neural craving responses similar to hunger. bioRxiv.
Baldwin, I.T. and Schultz, J.C., 1983. Rapid changes in tree leaf chemistry induced by damage: evidence for communication between plants. Science, 221(4607), pp.277-279.
Massalha, H., Korenblum, E., Tholl, D. and Aharoni, A., 2017. Small molecules below‐ground: the role of specialized metabolites in the rhizosphere. The plant journal, 90(4), pp.788-807.
Semchenko, M., Saar, S. and Lepik, A., 2014. Plant root exudates mediate neighbour recognition and trigger complex behavioural changes. New Phytologist, 204(3), pp.631-637.
Scala, A., Allmann, S., Mirabella, R., Haring, M.A. and Schuurink, R.C., 2013. Green leaf volatiles: a plant’s multifunctional weapon against herbivores and pathogens. International journal of molecular sciences, 14(9), pp.17781-17811.
Song, Y.Y., Zeng, R.S., Xu, J.F., Li, J., Shen, X. and Yihdego, W.G., 2010. Interplant communication of tomato plants through underground common mycorrhizal networks. PloS one, 5(10), p.e13324.
Sugimoto, K., Matsui, K., Iijima, Y., Akakabe, Y., Muramoto, S., Ozawa, R., Uefune, M., Sasaki, R., Alamgir, K.M., Akitake, S. and Nobuke, T., 2014. Intake and transformation to a glycoside of (Z)-3-hexenol from infested neighbors reveals a mode of plant odor reception and defense. Proceedings of the National Academy of Sciences, 111(19), pp.7144-7149.
Schwachtje, J., Minchin, P.E., Jahnke, S., van Dongen, J.T., Schittko, U. and Baldwin, I.T., 2006. SNF1-related kinases allow plants to tolerate herbivory by allocating carbon to roots. Proceedings of the National Academy of Sciences, 103(34), pp.12935-12940.
Bohman, B., Karton, A., Flematti, G.R., Scaffidi, A. and Peakall, R., 2018. Structure-activity studies of semiochemicals from the spider orchid Caladenia plicata for sexual deception. Journal of chemical ecology, 44(5), pp.436-443.
Allmann, S., Späthe, A., Bisch-Knaden, S., Kallenbach, M., Reinecke, A., Sachse, S., Baldwin, I.T. and Hansson, B.S., 2013. Feeding-induced rearrangement of green leaf volatiles reduces moth oviposition. Elife, 2, p.e00421.
Allmann, S. and Baldwin, I.T., 2010. Insects betray themselves in nature to predators by rapid isomerization of green leaf volatiles. Science, 329(5995), pp.1075-1078.
Lackus, N.D., Lackner, S., Gershenzon, J., Unsicker, S.B. and Köllner, T.G., 2018. The occurrence and formation of monoterpenes in herbivore-damaged poplar roots. Scientific reports, 8(1), pp.1-13.
Gilbert, L. and Johnson, D., 2017. Plant–plant communication through common mycorrhizal networks. In Advances in Botanical Research (Vol. 82, pp. 83-97). Academic Press.
Written by Libby Bowles
I’m a PhD Researcher at Prifysgol Aberystwyth, studying the perenniality syndrome in Grasses. I’m passionate about public engagement in science and the sharing of knowledge regarding the world we live in, especially the weird and wonderful.