Internal Clock and Light Exposure Regulate Plant Growth

Author:  Doshi Ojus

Date:  July 2007

Researchers at the University of California, Davis have described a molecular mechanism that plants use to regulate growth in their natural environment. The findings, published in the June advance online edition of Nature, outline a method of growth that involves the coordination of a plant's internal clock with its exposure to light.

Members of Assistant Professor of Plant Biology Dr. Julin Maloof's laboratory used infrared time-lapse photography and genetic engineering techniques to characterize a mechanism involving the degradation and activation of the proteins PIF4 and PIF5 in Arabidopsis. Breaking from traditional growth studies, the scientists replicated a plant's exposure to light in a diurnal environment, meaning that they observed it in a natural cycle of light and dark. Previous studies only used constant light or constant dark conditions.

"For many years most plant growth and circadian studies were performed in constant light or dark because it reduced the system to something that was easier to interpret," Maloof explained. "Now that we have a reasonable framework of how those systems work (through the studies of many labs over many years) we can start trying to study plant behavior in more complex growth regimes to look at how systems interact."

Maloof's group followed the activity of the PIF4 and PIF5 genes and found that they were activated during the day, turned off in the dark, and activated again very late at night. Their respective proteins, however, were degraded by light, so that most growth happened before dawn. This mechanism shows an important connection between the plant's internal clock and external light cues.

"Our work illustrates the importance of examining circadian phenomenon in a diurnal context," said Maloof. "It provides a detailed and elegant mechanism for interactions between the internal oscillator and external signaling."

In addition to being a probable paradigm for other clock/environment mechanisms, this research could help in the engineering of biofuels and other agricultural plants with enhanced growth properties, he said.

Written by Ojus Doshi