Plants Have a Clock

Plants, like many other organisms, have circadian clocks that help them anticipate various environmental and biological events that occur at precise times of the day. Processes like photosynthesis, fragrance emission and time of bloom are all regulated by this timekeeping mechanism.

Now, scientists report in the journal Nature that genes in certain plants keep infections at a distance with the help of the clock as well. Twenty-two genes in the plant Arabidopsis, all connected to the plant’s ability to resist infection, were expressed only from the evening onward, reaching their highest point at the beginning of day.

The timing corresponds with the formation of spores in a funguslike pathogen that attacks the plant and results in a condition known as mildew disease. The disease weakens the plant and forms a repugnant layer of mildew.

“From what we know, the pathogen forms spores at night and disseminates them at the beginning of day, so that’s when the danger of infection is highest,” said Xinnian Dong, a biologist at Duke University and one of the study’s authors. During the day, when the pathogen does not attack, the genes were not expressed.

This is the first time scientists have made a connection between the circadian clock and pathogen resistance, Dr. Dong said. She believes that if we analyze the complexity of the relationship between pathogens and hosts, and their circadian rhythms, there may be practical applications. Pesticide treatments could be timed to have maximum impact, for instance. Or it may even be possible to determine ideal times for administering medications in humans, she said.

By Sindya N. Bhanoo, www.nytimes.com. Picture by Wei Wang and Xinnian Dong.