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The Winter Garden displays a diverse range of plants to dramatic visual and sensory effect.
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Tick-tock – plants can tell the time too…

The Garden's circadian rhythm bedsThe Garden's circadian rhythm beds
Having turned our clocks back, we resign ourselves to decreasing daylight hours as we creep closer to the winter solstice. Did you know that plants have clocks too? Professor Alex Webb explains more…

By October, the leaves of the deciduous trees will have changed from green to red, orange or yellow before turning brown and falling. I can make this certain prediction about what will happen in October because the seasonal changes in the life cycles of plants, from seed germination to flowering and the fall of leaves, occur at defined times in the year.

This temporal sequencing of life happens because plants can measure time. Plants use an internal clock to count the hours of light, such as the shorter days of Autumn, to establish the season and control biological changes such as leaf fall or flowering in the Spring. Biologists call this a circadian clock, from the Latin “circa diem” meaning around a day.

While the circadian clock ticks deep within the cells of the plant, we can observe the results of its ticking using the naked eye, or time lapse cameras. A good example of how a plant is regulated by circadian clocks can be seen in the daily movements of the petals of plants such as daisies. This old English name of the “day’s eye” refers to the opening of the petals during the light of the day. This is to expose the reproductive organs of the flowers for pollination by day-active insects. At night the petals close to protect the reproductive material from the cold of night.

Remarkably the circadian clock can keep ticking even without the changes in light and temperature that occur across the day and night. This can be seen when we put daisy plants in constant light in a laboratory and watch the petals continue to open and close for many days, showing the ticking of the 24 hour circadian clock.

The circadian clock acts as the timing device, allowing plants to measure changes in daylength, regulate the time of year when plants flower, and therefore set seed. If we consider that the three most eaten foodstuffs on the planet are products of the seeds of wheat, rice and maize (sweet corn), we can conclude the correct functioning of the circadian clock is important for agriculture. My laboratory is working with the National Institute of Agricultural Botany on Huntingdon Road in Cambridge and Bayer CropScience to find ways to use our knowledge of the circadian clock to develop improved crop varieties.

The circadian display beds in the Cambridge University Botanic Garden demonstrate how plants tell the time and are in flower from Spring through to late Autumn.

Read more about Alex Webb’s research including latest news on the effects of sugars on the circadian clock by clicking the link to the left.

Publication Date
30/10/2017