One of winter's perennial surprises is the appearance of insects on warmer days. It's a reminder that some of Earth's organisms make their own antifreeze.
Biologists are only beginning to appreciate the subtle ways in which some organisms use this kind of cold weather protection. Indeed, while for many life forms the object is to prevent ice forming within body tissues, others find that carefully controlled icing has its advantages. These organisms aren't just cold tolerant, they're freeze resistant.
This remarkable ability was recognized during the 1970s by certain biologists such as John C. Duman at the University of Notre Dame.
As explained in a recent university announcement, Duman's research confirms what he and other investigators have suspected. Freeze tolerance arises from a combination of seemingly antithetical properties.
So-called nucleating agents induce ice to form in tissues surrounding the body cells of the organism at relatively high sub-freezing temperatures. This draws water out of the cells themselves preventing ice from forming within them. At the same time, an antifreezing agent -- typically glycerol -- keeps the cells from drying out.
In this way, the organism can go through freeze-thaw cycles without damage. As long as its body cells themselves do not freeze, it continues to live.
In 1976, Karl Erik Zachariassen and Harold T. Hammel, then at Scripps Institution of Oceanography, reported a study of freeze-tolerant beetles which supported this theory. A couple of years later, Duman, who was at that time working with Jean Patterson at the University of Toho in Japan, found that the bald-faced hornet uses this kind of freeze protection Since then, he has been studying the process in other insects.
Besides insects, some plants also may turn the normally lethal phenomenon of freezing to their advantage. A particularly striking example was reported last year by Zachariassen and his colleagues Bjorn Larsen and Olav Smidsrod at the University of Trondheim in norway and John O. Krog at the University of Oslo.
They found that an African plant (Lobelia telekii),m growing in the alpine zone on Mt. Kenya, regularly goes through a freeze-thaw cycle in which the heat released by freezing of water helps protect the plant itself. Hollow flower stalks, 5 to 8 centimeters in diameter and up to 2 meters high, are partly filled with several liters of a fluid within which ice crystals form when air temperatures drop below freezing. The heat released warms air trapped above the fluid and keeps surrounding tissue from freezing.
Such elaborate mechanisms for turning freezing to advantage suggest that Earth's life forms have subtle tricks for adapting to cold. As more is learned about these capacities, biologists may find ways to help crop plants thrive better in frosty lands.