For the first time, researchers have shown that plant growth is regulated by both an internal clock and external light.
Using time-lapse photography, post-doctoral researcher Kazunari Nozue, with colleagues from the University of California, Davis, and the University of Lausanne, Switzerland, found that the shoots of Arabidopsis seedlings show a spurt of growth once a day. They claimed that the timing of that growth spurt is controlled by both the plant's internal clock and its exposure to light, acting on two genes called PIF 4 and PIF 5.
Julin Maloof, assistant professor of plant biology at UC Davis, who is the senior author on the paper, described the discovery as an "elegant mechanism".
The researchers identified the two genes, PIF 4 and PIF 5, that are connected to plant growth and regulated by the internal clock.
The PIF 4 and 5 genes are "switched on" to make protein during the day, switch off after dark but then turn on again late in the night. But the proteins made by PIF 4 and PIF 5 break down when exposed to light. o while the internal clock drives transcription of the genes to produce proteins, external light removes the protein.
The PIF 4 and 5 proteins are thought to act as transcription factors that turn on other genes involved in growth.
The work is published online in the journal Nature.