Season after season, year after year, springtime comes. The sun shines, the baby birds sing, and the flowers bloom. These are all experiences we associate with spring. But why? Why is it that flowers are a springtime phenomenon? Scientists have uncovered specific cellular processes within plants that could answer this question.
It turns out that the time ticks away for plants just as much as it does for us. This is known as an “internal circadian clock.” A paper recently published in the Journal of Plant Research by Inoue et. Al describes a circadian clock as, “endogenous time-keeping mechanisms that allow organisms to anticipate and prepare for daily and seasonal changes in surrounding environments.” In other words, the internal circadian clock is the inner workings of plants, that allows them to change their behavior in response to different environments and then as a result, increase their survival. Circadian clocks within plants consist of, “multiple interlocking transcription/translational feedback loops” and many genes have been proven to control this process. These feedback loops are highly linked with external light/dark periods. Some examples are stomatal opening and photosynthesis. Scientists say that genes pertaining to photosynthesis are expressed and controlled by the circadian clock. However, gene expression is not the only process subject to the circadian clock. There are many post-transcriptional and post-translational alterations made within the plant’s cells that are controlled by the circadian clock. According to research done by Dr. Isabelle S. Booij-James and her team, phosphorylation of an essential protein involved in photosynthesis, protein D1 in photosystem II protein in chloroplasts, is directly related to the light reactions that occur inside plants.
The circadian clock in plants is also known to regulate the development of the plant during its life cycle. Flowering, or what is known as photoperiodic flowering, is the most studied developmental process regulated by the circadian clock. A transcription factor (proteins that affect gene expression) called CONSTANTS (CO) is known to affect flowering directly and to be regulated by the circadian clock. This transcription factor is regulated by numerous different proteins that all work in coordination with the circadian clock and light signaling pathways to activate transcription of the FLOWERING LOCUS T (FT), which causes the plant to flower. Therefore, it can be assumed that springtime light/dark conditions are specific ingredients to produce a flowering plant. But does it end there? No! Fascinatingly, the circadian clock within the plant regulates how open the petals of the flower are at different times of the day to optimize pollination when pollinators, such as bees and butterflies, are out and about.
So, when you stop to smell the roses, remember that they are just as much taking advantage of the springtime sunshine as you are.
If you want to learn more about flowering in plants, specifically in trees, watch this video by The Atlantic: