Plants that grow in the world's temperate regions have developed ways to help their fragile seedlings outwit the deadly chill of winter.

A period of cold weather lets seeds know when it's safe to germinate. A similar temperature-dependent system controls blooming.But scientists deciphering the secrets of these systems say the "all clear" signal for germination or blooming is more complex than was once believed.

"There is evidence that two or three physiological processes are involved in breaking dormancy," says Schuyler Seeley, a plant physiologist with the Agricultural Experiment Station at Utah State University.

Seely and his colleagues, USU plant scientist J. LaMar Anderson and graduate students Jose Ignacio del Real-Laborde and James W. Frisby, reported on their work at the 69th annual meeting of the Pacific Division of the American Association for the Advancement of Science.

Seeley has worked on several models of relationships between temperature, seed dormancy and blooming. The researchers have recently developed computer models that correlate development of seeds and plants with temperatures and with time of chilling or warming.

Seeley said that the creation of more accurate models of fruit development will help fruit growers in temperate regions predict plant development and will let them know when they need to take action to protect plants from frost damage.

The models could also be useful in tropical areas, helping growers circumvent the need for cold temperatures to break seed dormancy and initiate fruit production in plants from temperate climates.

The models could also be used to answer one of the nation's aesthetic questions, predicting the date of emergence of cherry blossoms in Washington. Seeley said the models may predict blooms reliably as much as 60 days in advance.

Understanding relationships between temperatures and dormancy can lead to ways to control plant development. For example, chilling might be accelerated by evaporative cooling at the optimum time or extended by applying plant hormones at certain times. Some caustic sprays seem to "shock" plants out of dormancy. The best long-term solution, however, is the breeding of plants adapted to a particular environment.

Some of the USU research involves dwarf peach trees, some no taller than one-half inch, whose growth has been stunted byinadequate chilling during seed dormancy.