Internal clock helps petunias know when to smell good

No one smells good all the time. The is having the right smell for the right moment, or for flowers, the right aroma for the right hours -- the hours when pollinators are out shopping for nectar.

Recently, researchers at the University of Washington discovered the mechanism that allows the common garden petunia to put out its refreshing fragrance with such impeccable timing. It turns out, the flower boasts a circadian clock that governs the release of pollinator-attracting chemicals.

A gene sequence called LHY helps petunias (and many other flowers) keep time, helping the plant know when to suppress their bouquet and when to up the perfume production process. The genes keep the flower's smell to a minimum until the sun starts to go down. Pollinators important to the petunia, including the hawk moths, are most active during dusk and early evening.

"Plants emit these scents when they want to attract their pollinators," senior researcher Takato Imaizumi, an associate professor of biology at Washington, said in a press release. "It makes sense that they should time this with when the pollinators will be around."

Researchers have long studied the LHY gene sequence -- in a variety of different organisms -- but this the first time scientists have connected the sequence to a flower's fragrance.

"Now we're finding out what the bridge is between the circadian clock and scent production and release," said Myles Fenske, a doctoral student in biology at the university.

Fenske is one of three lead authors on the paper, published this week in the journal PNAS.

To confirm the connection between genes and scent, researchers both suppressed and signaled LHY activity at different times of the day. Suppression caused the flower's fragrance to release early, while signaling delayed the release indefinitely.

"That was perfect," Imaizumi said of the experiment. "It is exactly what I would hope to see."