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Garden-variety tonic for stress: vitamins may invigorate leafy patients.

Does your coleus look a bit peaked? Do your snap beans lean drooping and stunted when they should stand tall? Have your young saplings taken on that ravaged look?

If so, they may be stressed.

But not to worry. Doc Norris may have just the remedy - a rejuvenating elixir, made from all-natural ingredients, that costs just pennies a dose. The new patent medicine not only restores vim and vigor to ailing vegetation, he says, but also helps plants ward off insect attack.

Sound like snake oil? No, just vitamins. However, because researchers are still working to formulate the most effective therapeutic doses, don't look for these tonics in garden centers, seed catalogs or farm supply outlets just yet. Norris hopes to see products resulting from his studies marketed later this year. Other labs, already eying his work, may add their own vitamin supplements to the commercial plant-protection arsenal by the end of this decade.

Plants suffer from a range of stresses - from heat and drought to air pollution and insect predation. "We've found that the plant doesn't differentiate between a lot of these different stresses -- say, insect feeding or a fungus attack versus exposure to sulfur dioxide," says Dale M. Norris of the University of Wisconsin-Madison.

Norris, an entomologist, has spent 40 years studying insect nerve cells and how they react to odors, such as pheromones, and other chemical cues. Over the past decade, he and his co-workers also have observed that the plasma membranes surrounding the cells of soybean plants contain stress-sensitive proteins very similar to those in the membranes enclosing insect nerves.

"These proteins are what we could call stress monitors," he says. They appear to represent a communications channel by which both animals and plants interpret and react to their environment.

Although the Wisconsin researchers have found direct evidence for these membrane-bound stress sentinels only in soybeans, Norris says indirect chemical evidence of their existence has turned up "in every plant we've tested."

When triggered by some stressful episode, these proteins appear to stimulate the production of "second messengers" -- intracellular chemicals that effectively announce the presence of an external threat, he says. On the basis of the transmitted warnings, the cells' nuclear apparatus decides whether or not to switch on the genes that code for the production of natural stress-defense chemicals. But if the stress sentinels become seriously damaged, Norris says, they may render plants effectively blind and defenseless.

"We have found that these sulfhydryldisulfide-containing [sentinel] proteins are very sensitive to oxidation [free-radical attack]," Norris told SCIENCE NEWS. Free radicals are among the most biologically damaging compounds in nature. Possessing an unpaired electron, these nearly ubiquitous chemicals wreak havoc by robbing an electron from a protein or other nearby molecule. "If you have too many free radicals," Norris says, "these proteins get denatured and no longer respond biologically."

What better way to protect the stress-sensing proteins, he reasoned, than to treat plants with free-radical-squelching antioxidants? So in 1987, Norris and his colleagues began administering vitamins C and E -- nature's premier antioxidants -- to plants. "And they worked," he says.

We've been able to apply them [C and E] in every conceivable way," from drenching the soil or painting a band around a tree trunk to spraying foliage or immersing a few leaves in a dilute bath, Norris says. "We've even treated seeds prior to germination and gotten food results on the eventual plants." Last year, he received a patent on treating plants with antioxidants vitamins.

While treating a single leaflet can elicit an effect throughout the plant, Norris says that's not due to the dispersion of the vitamin: The vitamin merely stimulates the plant to react systemically.

Indeed, "one problem that's starting to emerge is how to keep from overdosing," he says. "Very few people are going to have a scale that can weigh the small units [of vitamins] that they're going to need to add to a gallon of water." Extremely dilute solutions of the vitamins -- sometimes at mere parts-per-million concentrations -- appear to work best. Supplementing too heavily may actually jeopardize plant health, the Wisconsin studies show.

In the October 1991 JOURNAL OF CHEMICAL ECOLOGY, Norris and Fanindra P. Neupane (now at Tribhuvan University in Kathmandu, Nepal) describe studies of very young soybean plants on which the investigators painted a single leaflet with 0.5 milliliter of vitamin-E-laced oil. Cabbage loopers, a notorious larval pest, ate 60 to 75 percent more of the leaves from untreated plants than of foliage taken 48 hours after a plant had received a dose of 6.25 international units of the vitamin. Leaves emerging after vitamin treatment received equivalent protection. In fact, Norris says, as a plant grows, its new tissues -- including those emerging after vitamin delivery -- "tend to be the most responsive" to therapy.

And dose proved important. In this study, a doubled dose provided the biggest protection four days after treatment. In some cases, caterpillars given a choice ate nearly three times as much from leaves of untreated plants as from those dosed with vitamin E.

A research report on soybean plants treated with extremely dilute solutions of vitamin C in water has been accepted for publication later this year in the German journal CHEMOECOLOGY, Norris says. In this study, concentrations varying by a factor of 10,000 all increased a plant's ability to discourage cabbage loopers, although doses near the extremes of this spectrum were not as realiably effective.

Both of these studies assayed a plant's ability to ward off insect attack. In other studies, says Norris, the Wisconsin researchers have successfully used vitamins to induce resistance to microbial pathogens, weed killers, mechanical injury (such as bruising) and drought.

Vitamin E (alpha-tocopherol) is oil-soluble, while vitamin C (ascorbate) is water-soluble. Why should both work? Norris notes that the stress-sentinel proteins are very long; some cross back and forth through the cell membrane up to seven times. Along their length, "these proteins have very distinct hydrophilic [water-loving] and hydrophobic [water-hating] areas," he says. "So they're apparently susceptible to both [the hydrophobic] vitamin E and [hydrophilic] vitamin C."

However, preliminary data hint that "it's a little easier to get longer-term effects from vitamin E" - perhaps lasting up to three weeks. "I don't want to put vitamin C in a bad light, but right now it looks like 10 days is perhaps its maximum," Norris says.

Genetics also affect the therapy's efficacy, he notes. "When people treat their plants, they'll find some are going to respond better than others. And that's not because our work isn't sound or reproducible. It's because [even within a species] some varieties are more responsive." Norris says he'd like to help breeders identify which plants exhibit the greatest sensitivity.

Spin-off research may provide plant breeders -- who sometimes spend up to half of their time in the field screening plants for their susceptibility to stress -- with another benefit as well. Norris says he hopes to patent a chemical assay that will allow growers to distinguish innately vulnerable seedlings from stress-tolerant plants within two weeks.

Though he has focused on soybeans, Norris says these are not the only plants that benefit from antioxidant-vitamin therapy. His team has boosted the stress tolerance of snap beans, sweet corn, field corn, broccoli, coleus, ash trees and elms, often in multiple varieties of a species, he says.

Similar investigations have been conducted elsewhere, especially in Europe, notes Stuart F. Laermer of Nutley, N.J., director of industrial and agricultural products for Hoffman-La Roche Inc., the world's largest producer of vitamins. In the late 1980s, he says, Hoffmann-La Roche funded a literature search on the topic of vitamins in horticulture and plant science, turning up 155 citations. The company is now actively financing research in this area.

While Laermer questions whether the Wisconsin team's treatment is novel enough to warrant a patent, he says he fully supports the group's scientific conclusions. A wealth of studies show that "vitamin applications enhance stress protection and the stimulation of growth in plants - results that could potentially corroborate Dr. Norris," he says.

"In contrast to animal husbandry, where exogenous application of vitamins has often become routine practice, vitamins are hardly ever used in plant production," observes J.J. Oertli of the Institute for Plant Science of the Federal Technical University-Zurich in Lindau-Eschikon, Switzerland.

Laermer agrees, noting that vitamin therapy for plants "has met with some skepticism in the past, if only because much of the work . . . was done poorly." Well-designed experiments have indicated, he says, that antioxidants are "clearly beneficial for plant growth."

Nor are antioxidants the only vitamins showing promise for crops. "There are [other] vitamins that are really magic bullets," Laermer told SCIENCE NEWS. Because of patent interests, however, he said he would not yet unmask their identity.
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Author:Raloff, Janet
Publication:Science News
Date:Feb 8, 1992
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