New research shows that to prevent starvation at night, plants perform accurate arithmetic division. The calculation allows them to use up their starch reserves at a constant rate so that they run out almost precisely at dawn.

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"This is the first concrete example in a fundamental biological process of such a sophisticated arithmetic calculation," said mathematical modeller Professor Martin Howard from the John Innes Centre in Norwich.

Plants feed themselves during the day by using energy from the sun to convert carbon dioxide into sugars and starch. Once the sun has set, they must depend on a store of starch to prevent starvation.

Publishing their findings in an open access journal this month, John Innes Centre scientists explain that plants make precise adjustments to their rate of starch consumption. These adjustments ensure that the starch store lasts until dawn, even if the night comes unexpectedly early or the size of the starch store varies. They added that, in order to adjust their starch consumption so precisely, plants must be performing a mathematical calculation - arithmetic division.

Professor Alison Smith said, "The capacity to perform arithmetic calculation is vital for plant growth and productivity. The calculations are precise so that plants prevent starvation but also make the most efficient use of their food."

During the night, mechanisms inside the leaf measure the size of the starch store and estimate the length of time until dawn. Information about time comes from an internal clock, similar to the 'body clock' that governs human and animals' daily routines. The size of the starch store is then divided by the length of time until dawn to set the correct rate of starch consumption, so that, by dawn, around 95 percent of starch is used up.

Professor Smith added, "If the starch store is used too fast, plants will starve and stop growing during the night. If the store is used too slowly, some of it will be wasted."

The scientists carried out their analysis on the model organism Arabidopsis, from the Brassicaceae family, which also contains cabbage, broccoli, radish and oilseed rape plants.    

They used mathematical modelling to investigate how such a division calculation can be carried out inside the plants. The JIC researchers proposed that information about the size of the starch store and the time until dawn is encoded in the concentrations of two kinds of molecules (called S for starch and T for time). If the S molecules stimulate starch consumption, while the T molecules prevent this from happening, then the rate of starch consumption is set by the ratio of S molecules to T molecules, in other words S divided by T.