In the past, researchers have addressed this question by looking at differences between plants growing at normal temperatures and those growing at colder temperatures, such as differences in what types of sugars or fats or proteins they contain. However, there are a large number of these differences, and it's difficult if not impossible to separate those that cause changes from those that are responses to them. Xin is taking a different approach. He's spent the last year screening over 800,000 mutant Arabidopsis plants, plants whose DNA has been chemically altered. Because he was looking for negative regulators of the freeze tolerance process, he looked for plants that were able to survive freezing temperatures without the 39 degree conditioning period.
Negative regulators function somewhat like cancer suppressers.
When present, each prevents something from happening. Cancer suppressers keep a cell from becoming cancerous. In freeze tolerant plants, negative regulators keep the plant from wasting energy-producing molecules necessary for tolerating freezing temperatures unless it's cold. If the negative regulator is not present, then the plant goes ahead and develops the ability to tolerate freezes regardless of the temperature. The year of screening plants has paid off with 20 mutants that meet his criteria, plants whose genes that encode negative regulators have presumably been mutated.