How Flowers Know Spring Has Sprung

A 10-year-old, 5-foot tall tropical corpse plant in Brooklyn flowered for the first time last week, emitting its powerful stench for three days.

Luckily for Dutch tulip farmers, garden club members, and floral enthusiasts, many flowers in temperate regions of the world bloom each spring—and smell much sweeter.

Flowering plants evolved about 100 million years ago. As the planet's climate changed, some plants developed a seasonal strategy to lay low through the winter and bloom in the spring. These plants won't flower until they sense winter has come and gone, a process called vernalization.

Scientists have only begun to understand how flowers know when spring has sprung.

Cold is the key

Plants don't flower in the fall because their genes tell them not to by suppressing any flowering activity. But enough days in the cold turns the suppressing genes off and gives plants the green light to prepare to bloom, according to new research.

"In the fall season, they express a gene that's a very effective repressor of flowering," said lead researcher Richard Amasino of the University of Wisconsin-Madison. "We've discovered that during winter somehow prolonged exposure to cold turns off the repressor. With the repressor gone, flowering can occur."

Amasino announced his findings on Aug. 9 in Boston at a meeting of the American Society of Plant Biologists, of which he serves as president-elect.

Studies published in the journal Science this month have also identified the pathway of plant proteins that jump start flower buds.

Precision is key

Flowering before the vernal equinox can be deadly for a flower. Imagine a daffodil's despair if it flowers in February after a fluke warm spell. So precision is key.

Not only must flowers have a thermometer-like tool to measure the outdoor temperature, they also need to keep count of the winter months.

The trick to keeping track of winter isn't limited to the plant kingdom. Like flowers, insects have to measure and count cold days also, so that they don't hatch too early in the year. Amasino's team is now working to find out what helps plants measure the cold.

The research may some day be used to keep the vegetables in your garden under control.

"This is important agriculturally," Amasino said. "There are many crops—cabbage, beets—that we don't want to flower. Many of the cultivated varieties we use are never exposed to cold in a typical farmer's field growing season."

24-hour clock

While a lengthy winter dictates when a plant will first open its petals, a flower's daily hours of operation depend on day length.

In the 1920's researchers began growing plants under artificial lights. Experiments found that plants flowered only when they detected the correct period of "daylight," called a photoperiodic response.

Researchers at the Scripps Research Institute have been studying the internal clocks of plants, mice, and fireflies. Similar to humans, plants have circadian clock genes inside their cells that operate on a 24-hour schedule. The Scripps team has identified several clock genes.

Further understanding of circadian rhythms in plants may solve symptoms of jet lag, shift work, and sleep disorders.  

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