Conservation adopts a new dimension as scientists strive to save endangered species.
Within sausage-sized glass tubes on metal racks in a small, temperature-controlled room, 18 tiny sprouts of the cactus Ariocarpus agavoides bulge from hard, black seeds no larger than an oval pinhead. The transparent, jelly-like substance on which they grow glistens under the fluorescent lights overhead.
This is Guadalupe Malda’s "growth chamber." There may be more of these tiny plants here than anywhere else in the world.
"Many people think this species is extinct," says Malda, a doctoral student in botany at Arizona State University. The cactus is only known to grow in one location in Mexico, and Malda says no one has seen any there for a number of years.
Ariocarpus agavoides is listed as one of the world’s 12 most endangered plant species by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). It belongs to a whole group of cacti highly prized for their unusual appearance and rarity. Most Ariocarpus have been devastated by overzealous collection. Some species have been known to fetch up to $1,400 per plant in places like Germany and Japan, where trade in exotic cacti is almost a fetish. Some European cactophiles even organize “adventure” trips, advertised in collectors’ magazines, to hunt for cacti protected by law in Mexico and the American Southwest. Cacti are also threatened by overgrazing and habitat destruction.
The damage has been so great that CITES, which has global guardianship of endangered species, has placed all but one of nearly 100 cacti genera under its protection. Of at least 850 species endemic to the United States and Mexico, more than 60 are considered so threatened that international trade of plants collected from the wild is illegal. Permits are required to trade the rest.
Botanical gardens worldwide have long been trying to conserve endangered plants by sprouting new generations from permanent seed collections. But for some species, like A. agavoides, conventional planting doesn’t work so well.
With a growing technique called tissue culture, scientists like Malda are trying to save these cacti, which otherwise wouldn’t have much hope for survival.
Many species of cacti are very easy to grow. Some sprout readily from seed while others can be cultivated from cuttings rooted in soil. This kind of "artificial propagation" has become the mainstay of the horticultural nursery industry. Although threats to habitat still exist, many specialists say cultivation has dramatically reduced pressures on wild cactus populations once scoured for rare and tantalizing specimens. Most cacti now sold to collectors, landscapers, and household hobbyists are commercially grown.
But some cacti are more recalcitrant. They either produce few seeds, are difficult to grow in soil, or grow so slowly that commercial production is not profitable. Cacti belonging to the genus Ariocarpus, for instance, are so lethargic scientists have dubbed them "living rocks." Some take as many as 20 years to reach a diameter of just 2.5 inches. Many seed-grown species never come to resemble wild plants.
For these reasons, there is still a demand for wild-collected species on the international market. Those uprooted from their natural habitats are usually larger and much more unique than their cultivated counterparts. They display strange outgrowths and spectacular forms, are highly coveted by collectors with unquenchable appetites for the bizarre, and often sell for prices four times higher than plainer nursery-grown plants. Slow-growing and fragile species command the biggest bucks, from hundreds to thousands of dollars.
In 1986, six of the nine most commonly-traded cacti in Japan were slow-growing species severely threatened by overcollection. Conservationists contended that many of the plants were wild imports smuggled in to meet demand. Malda and other scientists hope tissue culture will help reduce pressure on the native populations.
Many cacti produced through tissue culture grow faster and larger than those raised by conventional techniques. The plants are nursed in a highly controlled environment on a substance called agar, a sugar-water mixture that resembles firm jelly. Nutrients and vitamins are added to the concoction to aid in growth. But the key ingredients are hormones.
Hormones are chemical signals. Two major groups exist in plants: cytokinins, which stimulate cells to divide, and auxins, which induce cell growth. When hormones are present in the right proportions, combinations of cell growth and division lead plants to produce roots, stems, or flowers.
In tissue culture, different concentrations of cytokinins, auxins, and other hormones are added to the medium to mimic stages of plant growth. The cultured plants absorb the hormones and respond accordingly.
"You’re making the plant believe it is internally ready to produce shoots or roots or flowers, because chemically it’s the same," Malda says.
Malda’s Ariocarpus seedlings are in a medium containing cytokinins that stimulate shoot production. Once the tiny plantlets are established, she can take cuttings or transfer them to auxin-rich cultures to induce root development. She predicts she will end up with about three new plants for every seed, and each seedling will probably support about three cuttings. At that rate, reproduction could continue indefinitely.
"After one year you could in theory get one million copies of the same plant," says Ralph Backhaus, Malda’s advisor and an ASU professor of botany. "As long as there is someone there to take the cuttings, you can get continuous growth."
That’s quite a feat in a species that takes at least five years to produce seeds in the wild, and whose natural cuttings don’t transplant well. Instead of yielding a new generation every five years, Malda’s Ariocarpus would reproduce with every cutting.
And Ariocarpus is just the beginning. In the species Coryphantha minima, Malda teased up to 30 new growths from each seed. Her collection of Pediocactus simpsonii grew from 10 seeds to 85 tiny plants in less than a year.
Some of her species have even displayed unusual characteristics. Obrecocius obregonia, for example, produced embryos—a seed-like growth that can be planted to begin a next generation.
“This is not common for cacti,” Malda says. The embryos mean the cacti have by-passed maturation, the growth phase leading to flowers and seeds. Most cacti take at least five years to mature. Malda’s O. obregonia were less than a year old when she spotted the embryos. “This is a real potential for propagation,” she says.
But the sailing isn’t all smooth. Before Malda can culture her plants in hormones, she must first figure out what amounts to use. The trouble is, what works with one species won’t necessarily work with another.
For instance, while her O. obregonia produced embryos, they failed to generate either roots or shoots. Part of Malda’s project is to figure out which chemical combinations work, and which work best.
Ultimately, Malda wishes to perfect her propagation techniques and use the plants she cultures for conservation. She could plant them in their original habitat and attempt to reestablish the species, but reintroduction is usually a last resort.
"You don’t want to put them back into the wild only to have the cows eat them," Backhaus says.
Malda’s ultimate goal is to sell the tissue-cultured plants commercially. She wants to return to her native Mexico, where her research in cactus conservation began.
Once she has perfected her techniques, Malda wants to train others to grow the cacti and sell them in Mexican nurseries. If her methods produce good enough cacti, the move could not only deter people from collecting plants from the wild, it could be an economic boon to people who were once paid pennies a plant to rip cacti from their backyards for export, Backhaus says.
One problem, however, is expense. Tissue culture requires specialized equipment to prevent contamination by bacteria and fungi that can steal nutrients from the plants and cause disease. Sterile labs cost at least $20,000 to start. Even in America, such money is hard to come by for research on very rare species, says Malda. And no one is sure what effect Mexico’s poor economic situation will have on funding.
Still, Malda is hopeful her research will eventually lead to improvements in conservation of cacti from both sides of the border. If her techniques are successful, industries might become as interested in tissue culture as they are in horticultural development. Then, she says, she will have made a difference.—Alana Mikkelsen
posted by Andrew Glazier at
11:44 PM
0 Comments:
Post a Comment
Subscribe to Post Comments [Atom]
<< Home