
Yesterday, the 18th of March of this crazy 2021, was a very special day: I had the article derived from my master's thesis published! In it, we demonstrate that the parasitic plant, the bizarre and almost alien dodder (Cuscuta racemosa) is capable of differentiating host species and changing its behaviour according to what it perceives! Furthermore, we noticed what may be the first empirical evidence of an process of attention in plants. You read ir right: attention. Theoretically the plant would be paying attention.
Brief contextualization: the work was done during my master's degree at the Federal University of Pelotas, in Brazil, in the Gaduate Program in Plant Physiology and in the Laboratory of Plant Cognition and Electrophysiology, LACEV. It was carried out with the guidance of Prof. Dr Gustavo Maia Souza and the participation of several colleagues, fundamental to the success of this research, it must be said! With the formalities done, let's get down to business, that is, the dodder.
This plant has no leaves or roots, and it doesn't even carry out photosynthesis (except for certain species, such as our Cuscuta racemosa, but still at a very low rate). It resembles a bunch of orange filaments that grow over other plants. When they do this, the dodders find a way to penetrate their host plants with structures called hyphae, which connect to the vases of the host plants and absorb their sap in a true plant vampirism. Many studies have shown that the dodder chooses the best plant to parasitise when it has more than one option, and this has led us to ask: if the dodder chooses between hosts, it must somehow recognise the difference between one and the other, and this recognition must cause changes in its functioning (its physiology). So, if we could observe what is happening inside the dodder when it perceives a host in the vicinity, would there be differences in this functioning depending on the perceived host?
Our hypothesis was that yes. In particular, we had some hypotheses. First, the dodder senses the presence of hosts near it. Second, depending on the presence and species of the host, the dodder would produce different amounts of pigments related to its poor photosynthesis. And, as we work with electrophysiology, we hypothesised that the bioelectric activity of the dodder would be different depending on the presence and species of the host present near it.
To test the hypotheses, we carried out some experiments placing dodder twigs inside a box and close to two different types of hosts: a bean plant or a wheat plant, in a scheme like the one in the figure below.
After leaving the dodders for a week in this condition, we measured the amount of pigments in the twigs. In addition, in another experiment, similar to the one in the figure, we performed an analysis analogous to the electroencephalogram, called an electrophytogram, in which we inserted electrodes in the dodders to monitor their bioelectric activity in the absence and presence of hosts in the box. The result was that, in fact, the dodder perceives when there are hosts nearby and changes its behaviour depending on the type of host present. For example, when it has no host near it, the dodder produced more photosynthesis-related pigments, which we interpret as an attempt to prolong its survival through some photosynthetic activity. The same was confirmed by the bioelectric activity, which is different when there is a host nearby.
Furthermore, the amount of pigments and bioelectric activity is different depending on the type of host present. That is, there is an electrical pattern associated with each type of host. The presence of the bean plant had one effect on the bioelectrical signals and the presence of the wheat another. In conclusion, the dodder recognises hosts of different species from a distance!
But the most surprising thing was another unexpected result of this work: due to a certain pattern of functioning of the dodder's bioelectric signals (namely, the signals became less "random", more organised, regular and predictable, in addition to being more strongly correlated) , we believe we have found the first empirical evidence of a process or state of attention in a plant! Possibly, the dodder was paying attention to its prey right there, close to it, focusing on a strategy to attack it and "concentrating" on it.
It is important to emphasise that our results are not yet an indisputable scientific fact! Although the article was published in a recognised and peer-reviewed scientific journal, that is, it is reliable, it only opens up the possibility of studying processes such as attention in plants. To become a universally accepted fact, there is still a lot of work to do. I hope this article starts off by causing a discussion in scientific circles. Some will disagree, some will agree, and I hope this will encourage other researchers to replicate these experiments, or do similar experiments. Only then can we evaluate the body of evidence and try to reach a consensus. Who knows what will come out of it?
However, it is clear that it is an interesting research and I am happy that, in the midst of the hardships and bitterness that science has been suffering in recent years in Brazil, we were able to publish it in an open access journal. That is, anyone, anywhere in the world will be able to download the article for free! Although it is not easy to publish in such journals, as it is quite expensive and resources are not always available, this time we did! This is wonderful because scientific knowledge belongs to humanity and should be accessible to all people.
Without further ado, the work was carried out at the Federal University of Pelotas, in Brazil, and is signed by Gabriela Niemeyer Reissig, Luis Felipe Basso, Luiz Gustavo Schultz Senko, Thiago Francisco de Carvalho Oliveira, Gabriel Ricardo Aguilera de Toledo, Arlan Silva Ferreira, Gustavo Maia Souza and me.
Those interested in reading more in depth can download the work on the Frontiers in Plant Science website. Thank you very much and until next time!
This post was published in Portuguese on the 19th of March, 2021.
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