About sugar and starch

Plant & zo

The science of plants and more

About sugar and starch

Just like us plants don’t like a lack of energy. During the day plants get their energy from sunlight and CO2. To prevent running out of energy during the night, plants turn part of that energy into starch. When there is not enough or no sunlight, plants breakdown this starch into energy. This happens during the night. But also, during twilight, or on a very overcast day. Researchers from Germany found out how plants decide to breakdown starch.

Using a computer simulation, the researchers predicted for different situations the breakdown of starch. In the simulation, the breakdown of starch was dependent on the amount of starch available and the time to dawn. The predicted outcomes were compared with the observed results in real life. For one of the situations there was a difference in outcome between the prediction and observations. This gave a lead in the search how starch breakdown is regulated.

In this situation, the researchers placed the plants from a normal day-night rhythm into a space with intense light for 24 hours a day. The simulation predicted that even though there was no night, the plants will breakdown starch in the second half of the expected night. In real life plants did not do that. There was no starch breakdown. This contrasted with plants standing for 24 hour a day in low light, like twilight, then plants do breakdown starch in the second half of the expected night. Indicating that there is something that prevents the breakdown of starch when there is enough light.

This signal can come directly from the received amount of light. Or it can be an indirect signal, like for example the amount of available sugar. To decipher between these two, the researchers analysed what happened with plants that got less light in the afternoon. This they compared with  plants that got enough light in the afternoon, but not enough CO2. In both situations plants make less sugars. And as the researchers noticed, in both cases they broke down more starch. Showing that the signal is coming from the sugars and not the light.

Sugar, thus, prevents the breakdown of starch. A reduction in the availability of sugar, like during a very cloudy day or during twilight, enables the breakdown of starch. Necessary even, to prevent an abrupt dip in energy. Allowing plants to keep going, even on a rainy day.


Hirofumi Ishihara, Saleh Alseekh, Regina Feil, Pumi Perera, Gavin M George, Piotr Niedźwiecki, Stephanie Arrivault, Samuel C Zeeman, Alisdair R Fernie, John E Lunn, Alison M Smith, Mark Stitt (2022) Rising rates of starch degradation during daytime and trehalose 6-phosphate optimize carbon availability. Plant Physiology, kiac162, https://doi.org/10.1093/plphys/kiac162

Do you want to read more about how plants calculate how much starch they can use? Go to Calculating plants

Published by Femke de Jong

A plant scientist who wants to let people know more about the wonders of plant science. Follow me at @plantandzo

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