Evening and morning plants

Plant & zo

The science of plants and more

Evening and morning plants

Just like people, plants have a biological clock. This helps plants to recognise when it is morning and when the evening starts. The biological clock consists, just like our analogue timepiece, through an ingenious radar work of interconnecting feedback loops. These are self-correcting so that not every passing cloud is signalling the beginning of the evening.

In plants, the biological clock is making sure that at sunrise, processes are started that are needed during the day, for example photosynthesis, and processes from the night, for example starch degradation into glucose, are ended. At the start of the evening the reverse takes place. The biological clock influences a lot of processes, like the growth of the plant, when it will flower, and how it responds to temperature fluctuations. And not to forget, it keeps track of the seasons.

Al together it is important for plants to have a biological clock that fits their environment. To further investigate this, British researchers analysed how the clock is behaving in 191 different tale cress (Arabidopsis) plants from different places in Sweden. To do this they used the photosynthetic activity to map each biological clock.

This showed that plants from the north of Sweden had a slightly quicker clock than those from the south. They also noticed that, just as by people, some plants were more active early in the morning, whereas others peaked late in the evening. Most of the plants were somewhere in between, but you have evening and morning plants.

The majority of the observed variation in the biological clock is due to an accumulation of small differences in clock-genes between the different tale cress plants. These differences the researches tried to find. For one gene they were lucky. For COLD REGULATED GENE 28 it turned out that a single mutation caused the clock to run slower. And it made the plants have their peak in photosynthetic activity an hour earlier in the day. But that was not all, this mutation also made plants delaying flowering.

As you can see a single mutation can have a big effect. Before you know it, you change from an evening into a morning person, ehm plant.


Rees, H, Joynson, R, Brown, JKM, Hall, A. (2021) Naturally occurring circadian rhythm variation associated with clock gene loci in Swedish Arabidopsis accessions. Plant Cell Environ. 44: 807– 820.

Published by Femke de Jong


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