Calculating plants

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Calculating plants

Plants are cool. Just that they can convert sunlight into sugar should justify this. But plants do so much more. One of the things they can do that I found just astounding is their ability to adjust the speed with which they turn starch into sugar.

Of all the energy plants get from sunlight half of it is stored as starch. Plants use this starch at night, turning it into sugars to use as energy. Plants do this in such a way so that at each point during the night the same amount of energy is available. The speed, with which plants turn starch into sugar depends on the total amount of starch available and the length of the night. A longer night results in a lower speed, while with more starch available the turnover speed increases. Showing that plants can calculate how quickly they can turn starch into sugar.

To show how astounding this is, imagine you have a stock that you need to distribute over a couple of days, so that on every day you have the same amount available. To do this, you need to know how big your stock is, and over how many days you need to distribute it. People can divide those numbers and write down the outcome to help us remember how much of the stock we can use each day. Plants, and specifically plant cells, can’t do that, at least not in a way people do this. They have a different method for making sure they use their supply of starch evenly during the night.

Researchers from England are finding out which method the plant use for this. The first clue they found in plants that miss the protein ESV1. These plants have trouble storing starch. They quickly breakdown the formed starch, even during the day, when there is more than enough sugar. It turned out that the starch in these plants is more accessible, easily reachable for starch breakdown enzymes. Restricting access, making starch less accessible for its breakdown enzymes is thus one requirement to evenly turn starch into sugar during the night.

Recently the researchers found a second clue. This time helped by a mutation in the enzyme beta-amylase 1. Beta-amylase 1 is one of the enzymes that breaks down starch into sugar. The interesting part is that the mutation found in beta-amylase 1 does not change anything about the enzymatic activity. The speed with which it turns starch into sugar has not changed. Nevertheless, plants with the newly found mutation use up their stock in starch quicker.

The researchers think reason why, is that something changed in the interaction between beta-amylase 1 and LSF1, a protein that helps enzymes to find starch. When beta-amylase 1 has the newly found mutation, it appears, that this interaction makes starch better identifiable or accessible. Because in absence of LSF1, plants with the newly found beta-amylase 1 mutation do turn their stock of starch evenly into sugar. Also, in absence of beta-amylase 1 is starch turnover rate normal. Suggesting that the interaction between beta-amylase 1 and LSF1 is regulating the restricted starch access.

How beta-amylase 1 and LSF1 interact, the researchers don’t know yet. Thus, it is also still a mystery what changes in this interaction when the newly found mutation in beta-amylase is present. But this research brings us one step closer to an answer to the question how plants adjust, depending on the situation, the speed of starch turnover. But even without knowing this, it is still astounding that plant can do arithmetic.

Literature

Doreen Feike, Marilyn Pike, Libero Gurrieri, Alexander Graf, Alison M Smith (2022) A dominant mutation in β-AMYLASE1 disrupts nighttime control of starch degradation in Arabidopsis leaves. Plant Physiology, Volume 188, Issue 4, Pages 1979–1992, https://doi.org/10.1093/plphys/kiab603

Doreen Feike, David Seung, Alexander Graf, Sylvain Bischof, Tamaryn Ellick, Mario Coiro, Sebastian Soyk, Simona Eicke, Tabea Mettler-Altmann, Kuan Jen Lu, Martin Trick, Samuel C. Zeeman, Alison M. Smith (2016) The Starch Granule-Associated Protein EARLY STARVATION1 Is Required for the Control of Starch Degradation in Arabidopsis thaliana Leaves. The Plant Cell, Volume 28, Issue 6, Pages 1472–1489, https://doi.org/10.1105/tpc.16.00011

Antonio Scialdone, Sam T Mugford, Doreen Feike, Alastair Skeffington, Philippa Borrill, Alexander Graf, Alison M Smith, Martin Howard (2013) Arabidopsis plants perform arithmetic division to prevent starvation at night. eLife 2:e00669 doi: 10.7554/eLife.00669