You Must Remember This

I give a talk called ‘Are plants immortal and how do they feel about this?’ I argue that in a theoretical sense, many plants are indeed immortal (but then so are lots of living things). As to plants having feelings about anything, I’m a little sceptical.

I’m always interested though in learning about how plants interact with the world and how they communicate with each other and within each plant. There is communication between cells, between different parts of a plant and between plants, it just works a little differently to what we humans normally think of as communication.

It’s risky to talk about any human concepts in relation to something like a plant but part of the Genes to Geoscience (G2G) philosophy is to raise ideas and see if they can be used to generate legitimate research questions.

So I was interested in what Ellen Simms from University of California, Berkeley would say about plant memory in her G2G presentation. Ellen raised this as one of the topics she would cover in a talk on the world of plant root symbioses (i.e. things that help each other around and in plant roots). It turned out that this memory is a uncertain concept at the moment and probably quite different to what Rick Shine was talking about in his earlier talk on evolutionary adaptation – Ellen's rememberance of things past was almost a ‘short-term memory’.

Ellen started her presentation by asking why plants don’t ‘cheat’ bacteria (Rhizobium) that live in the roots of some plants producing nitrogen products and taking carbon from their host. Through some neat experiments involving breeding Rhizobium with some curious traits such as ‘scabbing’ for the plant, where a Rhizobium keeps working when its colleagues go on strike, sort of... A ‘stubbornness’ trait was another.

[By the way, as a slight aside, Ian Paulsen from Macquarie University gave a passionate talk at G2G about bacteria. Bacteria, he said (and so do many) run the world. They are the most dominant life form in terms of numbers, distribution and biomass. Everything depends on them to function. There is amazing diversity within species – 100s of unique genes in each strain and sharing only about half their genes with fellow species members. This is all because they swap DNA a lot, and can pick up new traits easily. Being so adaptable, they find it easy to run the world...]

Back to these rooty bacteria. Cooperative strains turn out to do better. These experiments give power to the bacteria to negotiate more strongly with the plant. The plant can still make choices but not in the long term if the bacteria have these unusual traits.

But memory? Well there may be time lags in these interactions. Ellen said that ‘inducible defenses’, where  an organism develops resistance to something after being damaged by it in their first encounter, is well known and accepted. Could previous contact with Rhizobium strain (cooperative or otherwise) alter future interactions, perhaps through change a change in its genetic makeup? Perhaps, said Ellen.

This would be a behavioural trait rather than an evolutionary change but could possibly be carried through to offspring in some cases. However there may be interesting feedbacks between plant and environment which are not reflected in evolution.

This is all getting a bit technical and takes me personally beyond where I’m confortable without a few primer lectures. But I do like these kind of questions when they are turned into serious research problems rather than just something that sounds nice.

Image: A picture of a Rhizobium bacterium as seen through a Transmission Electron Microscope. I’ve copied it from the following website: http://microbezoo.commtechlab.msu.edu/zoo/zdrr0101.jpg.