X-Message-Number: 23637
From: "Basie" <>
Subject: Ice Stakes Through the Heart 
Date: Mon, 15 Mar 2004 20:13:37 -0500

Winterfat Seeds Take Ice Stakes Through the Heart




 Sharp ice crystals in the seed embryo mean instant death for most
seeds--but not for those of winterfat, a low-growing shrub that thrives from
the Yukon to Mexico. ARS studies have shown that sopping wet winterfat seeds
from Wyoming, Colorado, and Saskatchewan, Canada, can survive temperatures
at least as low as  22oF.

So how does this native seed of the spinach family do it? And, can this
ability be transferred to major crops?

Terry Booth, a rangeland scientist with USDA's Agricultural Research Service
in Cheyenne, Wyoming, is going to great lengths to find out. Most recently,
he visited ARS cytologist William P. Wergin in Beltsville, Maryland, to look
at the seeds through a scanning electron microscope specially designed to
view frozen tissue.


 Booth soaked and froze the seeds to simulate the West's freeze-thaw cycles.
Particularly in the spring, seeds often get wet from snowmelt during the day
and then, overnight, the water in the seeds turns to ice crystals. Or the
seeds get wet and start sprouting during a warm spell, only to be frozen by
winterlike spring storms.

Booth, working with Yuguang Bai, who is with Agriculture and Agri-Food
Canada in Kamloops, British Columbia, and Jim Romo, with the University of
Saskatchewan, found that water absorption before germination is greatest for
seeds soaked at 40oF or lower. Most seeds have a greater risk of freezing
damage as their water content increases.

Winterfat, however, often grew better when it had been soaked at cold
temperatures before freezing. Seedling vigor also varied by where the seeds
were collected, indicating that the plants have evolved so that the
germination requirements of the seeds fit local climate variations. "So it's
generally best to plant seed collected locally," Booth says.

Under magnification, Booth saw ice crystals in the embryos of seeds that
were frozen at  22oF before being plunged into and stored in liquid nitrogen
to preserve any internal ice crystals, as well as nearby tissue. What
surprised him was that the tissue was freeze-dried, with only occasional
large ice crystals and no indication of normal cellular structure.

"A key part of winterfat's tolerance to freezing seems to be its ability to
hydrate, dehydrate, and rehydrate again without significant damage," Booth
says.

That intrigues Booth because of his suspicion that winterfat may fight ice
with ice. The hairy layers that cover winterfat seeds appear likely to
promote ice crystal formation. If ice crystals form first in the outer
layers, these crystals may suck water from the embryo, aiding a
freeze-dehydration process that limits damage caused by embryo ice. It may
keep the largest crystals out of the embryo.

"But we need to spend a lot of time analyzing photographs taken through the
microscope before we can reach any conclusions," he says.

Booth finds the winterfat shrub's ice tolerance as interesting as that of
the Antarctic nematode that is the only animal known to survive with ice in
its cells.

But there is a very practical purpose to Booth's research. Winterfat is
important as a food source for cattle in the western United States and as
nesting cover for ducks on Canadian prairies. For the latter reason, Ducks
Unlimited, Canada, funded part of the research. The U.S. Bureau of Land
Management, the USDA Forest Service, and mining companies plant winterfat on
degraded rangelands and strip-mined areas.--By Don Comis, Agricultural
Research Service Information Staff.

D. Terrance Booth is at the USDA-ARS High Plains Grasslands Research
Station, 8408 Hildreth Rd., Cheyenne, WY 82009-8899; phone (307) 772-2433,
fax (307) 637-6124.

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