The Triumph of Seeds (16 page)

Nowhere else in nature can you find a setting quite like a soil seed bank. If dormancy compares to suspended animation, then seed banks represent suspended competition: hundreds or thousands of fierce rivals, from many species and generations, all lying side by side together in wait. When the right conditions suddenly appear (particularly following a fire or other disturbance), they trigger an intense struggle to get established. This competition among so many near neighbors has been a driving force in seed evolution, influencing everything from seed size to the speed of germination to the quality and quantity of food reserves. Some experts believe that seed banks even introduce new genetic variation into plant populations, since the DNA in older seeds often begins to degrade and
accumulate odd quirks. For the people who study seed banks, their surprising diversity and longevity can even inspire use of the rarest punctuation mark in science, the exclamation point. Charles Darwin once sprouted 537 seeds from three tablespoons of pond mud “all contained in a breakfast cup!”

Because they endure so long, seed banks can provide fascinating glimpses into the past. In Methuselah’s case, the “bank” was an ancient storehouse, but even in natural settings the seeds preserved in soil often include species that have disappeared from the landscape. Ecologists turn to seed banks when they want clues about historical habitats—what plants used to grow where. Darwin’s fascination with seeds began when he observed rose mallow, a plant of fields and gardens, sprouting where a new roadbed was being dug through a dark forest. He concluded that the seeds must have been in the soil “undisturbed for ages,” remnants from a time before the trees, when the landscape was open and cultivated. The most dramatic examples of rediscovery come when soil disturbance reveals long-forgotten seed banks, sometimes in unexpected places. In the spring of 1667, Londoners stood amazed as their city burst into blossom. Fields of golden mustard and other wildflowers suddenly appeared, spreading north from the River Thames, where, six months earlier, the Great Fire had razed thousands of homes and buildings, exposing bare ground and a seed bank buried for generations.

Seed banks may give us a glimpse backward, but for plants, the whole notion of dormancy remains focused on the future—dispersing their progeny forward in time. Perhaps no one is more conscious of this than gardeners and farmers, who find themselves pulling weed sprouts from the same patches of ground year after year after year. In fact, it was a group of frustrated farmers that inspired Professor William James Beal to embark on what has become one of the longest-running scientific experiments in history. A botanist at the Michigan Agricultural College (now Michigan State University), Beal started his project in the fall of 1879 in response to an appeal from local farmers. They wanted to know how many years of
pulling and cultivating would exhaust the weed seed in their fields. To find an answer, Beal carefully buried twenty glass bottles on a hill near his office. Each bottle contained fifty seeds from twenty-three local species, chosen “with the view of testing them at different times in the future.” Over the next three decades, Beal dug up one bottle every five years, planted the seeds, and kept track of how many still germinated. When he retired, he handed on the experiment to a younger colleague (complete with a “treasure map” to the secret location of the buried seeds). Later caretakers extended the time frame, so that the last “Beal bottle” won’t be exhumed until 2100. It’s unknown whether descendants of those original farmers are still working the same fields, but if so, we know they would still be yanking up weeds like moth mullein and dwarf mallow. Seeds of both species germinated readily from a bottle dug up in 2000, after 120 years beneath the soil.

Many people now regard Beal’s experiment as a novelty, a charming holdover from the era of the great nineteenth-century naturalists. His simple idea continues to remind us, every few years, that seeds can live a long, long time. But while modern research methods have grown more complex, Beal’s work foreshadowed major developments in the study of seeds. Never before have scientists tucked away so many seeds for the future—billions of them, from thousands of species. But instead of glass bottles, we now store seeds in high-security vaults and frigid arctic caves. Like Beal, modern seed savers take out their specimens every so often and germinate them; but unlike the good professor, they are not trying to understand old seed banks. Instead, they are creating new ones.

CHAPTER SEVEN

Take It to the Bank

The work is in the hands of Prof. Vavilov. . . . In his travels through Turkestan, Afghanistan and neighbouring countries and by a vast correspondence, collections of seeds of wheat, barley, rye, millet, flax, etc., have been brought together on a great scale. The central office is in Leningrad and occupies a very large building, in great measure a living museum of economic plants as represented by their seeds.

—William Bateson,
Science in Russia
(1925)

H
orsetooth Reservoir fills a six-and-a-half-mile canyon due west of Fort Collins, Colorado. Four dams hold back the water, their high earthen walls clearly visible from various parts of town. Should one or more of them fail, floodwaters would reach the city center in less than thirty minutes, too soon for any organized evacuation. A government study concluded that all or parts of the city, as well as several other communities downstream, “would be severely damaged or destroyed.” Reconstruction and recovery estimates top $6 billion.

There is one building, however, that is expected to do just fine. It lies on the edge of the Colorado State University campus, wedged between the ROTC center and a track-and-field facility. The name on the door reads National Center for Genetic Resources
Preservation, but most people still know it by its former name: the National Seed Bank. A casual observer would never guess that its nondescript cinderblock walls house laboratories and cryogenic vaults built to withstand earthquakes, blizzards, long-term power outages, and catastrophic fires. And on the off chance that the Horsetooth dams should burst, the building is designed to float.

“There’s a double foundation,” Christina Walters explained as we passed through a wide interior door. “It’s like a building within a building.” The seed collection lies inside that central core, safe from as much as ten feet of floodwaters. “They were thinking about tornadoes, too,” she added. “The walls are reinforced concrete. You couldn’t hurt this place with a Cadillac going 75 miles per hour.”

It’s not clear why anyone would assault the National Seed Bank with a Cadillac, but I laughed at the image. I did a lot of laughing with Chris Walters. An energetic woman of middle years, she talked about seeds with a charming mix of intensity and humor, and after every joke her eyes kept smiling long after the conversation had moved on. “Let’s go in,” she said, and another door whooshed open in front of us. Inside, lights brightened automatically as we walked by rack after rack of long, movable shelves, the type that libraries use to save space. And with more than 2 billion specimens in the collection, space is at a premium at the National Seed Bank.

“We’re part of the Department of Agriculture, so crops are definitely a focus,” Chris explained. The collection includes varieties of every imaginable food plant as well as samples of their closest relatives from the wild. The idea isn’t just to stockpile popular crops, but to save the range of genes that make them useful—from subtleties of flavor and nutrition to drought tolerance or resistance to disease. Seed banks store their thousands of varieties with a larger goal in mind: preserving, and better understanding, diversity itself. “What’s this?” Chris asked, snatching a silver foil bag from the nearest shelf. “Ah, sorghum,” she said. “I love sorghum.”

It’s safe to say that Chris Walters loves more about her job than the sorghum. She started at the seed bank as a postdoctoral fellow in
1986 and worked her way up to supervising the entire research program, from germination to genetics. Like Derek Bewley, she credits her passion for plants to a grandfather who had a farm. Her own family moved a lot and never even planted a garden, but she remembers begging her mother to buy her the little ornamentals sold at grocery stores. “They were just coleus plants,” she said, laughing. “You know, the ones with the purple leaves!” In college, her botanical interests began to focus on seeds, but it wasn’t always smooth sailing. One professor suggested she’d be better off studying “real plants.” But Chris persevered, specializing in desiccation, longevity, and physiology. Thirty years later, there are few people in the world with a better understanding of just what goes on (and what doesn’t) inside a dormant seed.

“I’ve been in here long enough,” she said suddenly, putting the sorghum back and heading for the door. I was happy to follow. Seeds last a lot longer if they’re cold, and massive refrigeration units keep the collection room chilled to a constant 0°F (–18°C). We exited shivering, with clouds of vapor swirling around our feet, and I now understood why the coat rack outside was draped with parkas and winter jackets. The tour continued to another vault below, where seeds were kept even colder in steel vats of liquid nitrogen. “Seeds have different personalities,” Chris told me, and explained how manipulating two critical storage factors, temperature and humidity, helped them find the best fit. When they got it right, the results could be dramatic. A grain of rice might stay viable for three to five years in nature, but could live for two hundred years at the seed bank. Their wheat specimens did even better, on track to last twice that long. “There’s no such thing as immortality,” she qualified. “Nothing lasts forever.” But seeds in a facility like the National Seed Bank come pretty darn close.

When we reached her office, I asked Chris to explain how seeds do it—how a seemingly inert object could survive for so long. Like every other expert I talked with, she immediately pointed out how little we really understand about seeds. But then she honed in on the
things that scientists do know. “When a seed dries out, the enzymes slow down and the molecules stop moving,” she explained, shifting piles of books and papers from two chairs so we could find a place to sit down. “Metabolic activity basically grinds to a halt.” Then she produced illustrations, diagrams, and even an electron micrograph of desiccated seed cells. With the water gone, they looked like crumpled plastic sacks clumsily stuffed with lumps. If you’ve ever let your three-year-old bag the groceries, you’ve seen something similar. “It’s a mess in there,” Chris said, “and very hard to study because you can’t see anything.” But Chris’s work does show that the reactions necessary for a plant cell to function, the very basics of metabolism, rely on water. Take out the water and everything stops. Put it back in, and the seed comes alive.

I asked her if a packet of dry soup mix might be a good analogy—it’s just a jumble of stuff, but when you add water you end up with a tasty meal. “Yes, to a point,” she said, and then frowned. “The difference is what happens when you put the water back in. Soup mix gives you soup, a bunch of ingredients floating around at random. In a seed you get organized, functioning cells. Somehow, desiccated seed cells have the ability to remember and regain their structure. That’s unusual. Most cells can’t do it.” Then she looked across at me and the laughter was back in her eyes. “If we dried your cells out and then added water, we’d get soup.”

Luckily for me, and for most members of the animal kingdom, life and reproduction don’t require surviving desiccation. But there are a few creatures who have learned this trick: certain nematodes, rotifers, tardigrades, and a group of tiny crustaceans familiar to generations of comic-book readers. Though they don’t actually wear crowns or lipstick like the pictures in those famous back-page ads, the brine shrimp sold as Sea-Monkeys are no less remarkable. Like seeds, their dried eggs can survive for years—in the wild or in mail-order packets—and their cells remember exactly how to reassemble themselves as soon as they land in a fishbowl. Experts now think that desiccated seeds and Sea-Monkeys have a lot in common, preserving vital functions in a glass-like state within their cells. Medical researchers recently mimicked this system to create the first stable dry vaccines for use in places that lack refrigeration. “Desiccation was definitely the inspiration,” one measles expert told me. They started with brine shrimp, he explained, but had their best results when they suspended live vaccine in
myo-insitol
, a sugar
extracted from rice and nuts.