Trees and other plants which live for several years must cope with conditions ranging from drought and high heat in summer to freezing cold in winter. To cope with cold weather, many become dormant in winter, stopping growth and slowing down their metabolism and energy consumption. This results in the formation of annual tree rings in their woody stem, providing a direct record of rhythmicity.
Researchers investigating the molecular and genetic basis of dormancy took samples from dormant trees at midday, and analysed which genes were active. They were surprised to find high levels of a circadian clock component which is usually turned off during the daytime. Further analysis of dormant Chestnut trees showed that the circadian clock is disrupted during dormancy, and restarts when the plant is exposed to warmer temperatures. This disruption could control changes in the tree’s processes to help it survive winter.