Emergency gardening: labs step in to help conserve the rarest plants on earth - csy

Science News, August 9, 2003 by Susan Milius

"One of the challenges of working on the last few [plants] is that you can't destroy anything," she says.

She quickly decided that the petioles, the little stems that connect a leaf blade to a twig, looked most promising as a source of unspecialized tissue. However, Murch counted four fungal diseases and three bacterial ailments afflicting the plants, not to mention infestation by an abundance of insects. The last remnants of a species often are sickly, she says.

Murch gave some plucked leaf-stem samples a big wallop of antibiotics and then spent 3 weeks weaning the plant bits from the drugs by reducing the dosage a little every 48 hours. Only then did she expose the tissue to cocktails of hormones and nutrients. A round of tests generally takes 7 to 10 days, after which Murch works out another set of cocktails and tries again. "You just have to work through the possibilities," she says.

The Kanaloa bits didn't do much for several rounds of testing, but finally, embryo tissue started to form. What did the trick was a mild auxin mixed with a strong cytokinin, one used commercially for defoliating cotton plants to ease harvesting.

When she saw her success, did she whoop and hug people? "No!" she says. "You don't get excited until you can do it again."

The youngsters aren't out of the climate-controlled growth chamber yet, but the planet now has a new generation of 20 Kanaloa seedlings about an inch tall. This summer, Murch is working on repeating the experiment.

GLOBAL COLLEAGUES Among tissue culture specialists, scientists who specialize in discovering the requirements of rare species don't reach anywhere near the numbers of what Murch calls "the corn-and-soybean crowd." Yet the rare-plant specialists have figured out how to grow dozens of rare plants.

The Lyon Arboretum in Honolulu has had at least limited success in figuring out how to culture some 300 rare species, says Nellie Sugii. One of her more dramatic projects began with a batch of little green fruits--they looked a bit like grapes, she says--on a stem delivered by Ken Wood in 1998. He'd visited one of the last half-dozen known members of Tetraplasandra flynii, a tropical tree species, and found half-ripe fruit.

Sugii extracted the embryos and nurtured the botanical equivalents of premature babies. After 6 months, with the embryos turning brown, "I was worried," she says. She couldn't bear to throw them away though, and suddenly they began to grow. "Now, in the lab, you can't throw anything away," she says.

The Royal Botanic Gardens, Kew in England also hosts a sweeping effort to propagate rare, fragile, or cantankerous species from around the world. They've been particularly successful with sterile-tissue-culture propagation of arid-zone succulent plants, such as cacti, which tend to rot when disturbed.

Some 30 rare North American plants are now under study by tissue-culture specialists at the Cincinnati Zoo. Endangered species of pawpaw trees in Florida, for example, grow what botanists call recalcitrant seeds, which don't survive drying and freezing in seed banks. "We started with the four-petaled pawpaw--the shoots looked really good, but we couldn't get roots for a long time," says Valerie Pence. She and her colleagues there have now succeeded in culturing three of these pawpaws, she reported in June at the Portland, Ore., meeting of the Society for In Vitro Biology. Her colleague Bernadette Plair also reported a way around the seed-bank problem. For the dwarf pawpaw, the researchers can now pack shoot buds inside gelatin beads, freeze them, and then thaw the plant tissue for culture.