Detoxifying Desert's Manna.
For thousands of years, people dwelling in parched regions of the world, from northwest China to Ethiopia's highlands, have been cultivating a lovely flowering legume. The entire plant--stems and all--nourishes a host of domesticated animals. People roast the seeds for snacks, cook them into a protein-rich porridge or gravy, and grind them for baking into a hearty bread.
To families farming some of the poorest soils on Earth, this grass pea (Lathyrus sativus) would appear to be nothing less than "manna from heaven," observes Peter S. Spencer of the Oregon Health Sciences University in Portland. It thrives when and where other crops won't. Poor soil? No problem. Range lands undergoing a protracted drought? No problem. Torrential monsoon flooding? No problem.
Well, there is one problem, and it's serious, the neurotoxicologist points out. The grass pea produces an amino acid that can destroy a person's nerves.
During prolonged droughts, when alternative crops shrivel, people often make the grass pea a dietary staple. Yet when consumed in large quantities for just 2 or 3 months, the untreated seeds can trigger a disabling spasticity known as lathyrism. Unless affected people find other sources of food quickly, their condition could worsen, and they could eventually lose all use of their legs.
In the rural villages where lathyrism tends to occur, wheelchairs aren't available and they wouldn't easily traverse the terrain. In the worst cases, the victims can get around only by crawling. Moreover, Spencer points out, because men 18 to 40 years old have proved most vulnerable to lathyrism, affected communities tend to lose their breadwinners to this crippling, incurable nerve degeneration.
It was against this backdrop last month that Adel El-Beltagy announced that the International Center for Agricultural Research in the Dry Areas (ICARDA) in Aleppo, Syria, had succeeded in breeding virtually toxinfree cultivars of L. sativus. The accomplishment, which took some 15 years and cost more than $1 million, has produced strains offering the yield, taste, and environmental ruggedness of the original plant.
Says EI-Beltagy, the institute's director general, ICARDA's breeders transformed poor farmers' potentially devastating "option of last resort" into a safe alternative.
And none too soon, lathyrism epidemiologists contend. In Gojam, Ethiopia, for instance, "the [cumulative] prevalence of spastic paraparesis [lathyrism] is 7.5 per 1,000 individuals--which is unbelievable for a neurodegenerative disease," Spencer notes.
Fernand Lambein of the University of Ghent in Belgium and his colleagues described a new lathyrism epidemic in northwestern Ethiopia's Wello area in the July 24, 1999 LANCET. Crippling at least 2,000 people, it was triggered by the drought of 1995 and 1996, which wiped out nearly all local crops other than the grass pea. This episode proved so serious that nearly one in five affected individuals was left "a crawler," the researchers noted--meaning the victim lost all ability to walk. That's at least four times the proportion of such severely affected cases that normally occur.
Droughts in Bangladesh during the early 1970s triggered an even more dramatic plague of lathyrism that disabled up to 70,000 of its victims, according to neurologist Anisul Haque of the Bangabandhu Sheikh Mujib Medical University in Dhaka. The outbreak, which he notes left some of these individuals quadriplegic, hit a few regions unusually hard, permanently disabling 20 out of every 1,000 inhabitants.
Among people eating the same amount of toxic grass-pea seeds, only a few typically develop the disease, Lambein has found. His data hint that dietary factors, such as deficiencies in trace minerals, might foster human vulnerability to the pea's toxin. Livestock rarely show poisoning symptoms.
Haque notes that recent public health campaigns have been trying to hammer home the importance of trying to detoxify the seeds before cooking them. However, he told SCIENCE NEWS, "we still find new cases in young adults." Though his periodic visits to heavily affected regions suggest that "the incidence is not as high as in the early 1970s," it's not clear how much the rate has fallen.
E. Ann Butler, a legume specialist with the Paleoethnobotany Institute of Archaeology at University College London, has been studying the role of L. sativus in the traditional Ethiopian diet. Her field investigations show that villagers continue to eat the grass pea despite being "very aware" that it can cause debilitating disease. Among local women, she finds, the traditional wisdom handed down is that these legumes should be detoxified before cooking.
She therefore contends that people fall victim to lathyrism not because of ignorance so much as climate and economics.
During dry spells, people can lose access to the extra water required to leach out the seed's poison, which is water soluble. Heating also degrades this amino acid, which is why boiling is the preferred way to detoxify the seed, notes Clayton G. Campbell, a retired Lathyrus breeder at Agriculture Canada's research station in Morden, Manitoba. He notes that during droughts, however, villagers are as likely to lack fuel as water.
Even where water and firewood are available, Butler finds, pretreating "is not always sufficient to render [grass peas] safe."
In Ethiopian villages, Butler recently collected small portions of grass-pea cuisine that had been prepared from peas pretreated with 10 minutes of soaking in hot water. She then had the samples tested by chemists at Kings College, London.
The results, which she reported earlier this month at the International Workshop on African Archaeobotany in Frankfurt, Germany, show that "levels of ... the lathyrism-causing toxin are not appreciably reduced by the detoxification methods used." More extensive pretreatments, including boiling the peas, are thought to remove more--but still not all--of the poison.
Over the past few decades, several research centers have been investigating the activity of grass-pea toxin. The unusual amino acid bears the unwieldy name beta-N-oxalyl-L-alpha-betadiaminopropionic acid, which is abbreviated as ODAP. Scientists speculate that in the grass pea, this toxin probably confers resistance to pests or climatic extremes.
More important from a human perspective, Spencer notes, the amino acid seems to masquerade as a signal molecule, called glutamate, that's found in animals. This natural compound is similar to the flavor-enhancing commercial food additive monosodium glutamate (MSG). Spencer's team and others have been teasing out why ODAP, acting as a glutamate mimic, proves so toxic.
ODAP seems to kill nerves through overstimulation.
Individual nerve cells carry electrical impulses over long distances, such as from the brain to the lower spinal cord. To transmit signals across the gaps separating adjacent cells, the ends of neurons produce chemical clarions. Glutamate is one such chemical messenger. When it docks with its receptor on the target nerve cell, it helps excite that neuron to generate its own electrical impulse.
Glutamate receptors come in several flavors, Spencer says. One type, called AMPA, triggers the fast excitatory signals running through the brain and nervous system. It's these glutamate receptors that ODAP turns on, Spencer's research shows.
In fact, he notes, ODAP can so over-stimulate the AMPA receptors that nerve cells can "experience exhaustion and, ultimately, death." The most vulnerable neurons, Spencer found, are those that regulate leg movement.
Damage to them explains the strange scissored gait of many lathyrism victims. In the disease's early stages, legs develop a muscle rigidity and spasticity, forcing people to walk by crossing one limb in front of the other. Weakness and intense aching may also plague the affected muscles. In advanced cases, Spencer says, the victim's lower limbs "become useless--locked in a cross-legged, fixed position."
ODAP concentrations tend to naturally hover between 1 and 2 percent by weight in most grass peas, notes Campbell, now with Kade Research in Morden. Eating small quantities of legumes harboring these concentrations is harmless. Only when a person's grass-pea consumption reaches about 30 percent of daily calories and persists for several months will lathyrism typically develop.
Because of the seriousness of lathyrism and the popularity of grass peas in drought-prone regions, ICARDA launched a research effort about 15 years ago to develop low-ODAP strains.
A similar program had already been under way at Agriculture Canada's Morden lab for a couple years. Starting with an Indian line of grass peas, this federal project bred nine different low-toxin strains. "Our first variety," Campbell recalls, "came out with just 0.06 percent ODAP." Eventually, his team created a line that reliably produced just 0.01 percent ODAP.
As natives of India, however, many of these strains didn't offer high yields under conditions encountered elsewhere. Moreover, the new seeds often looked different from those cultivated in Nepal, Ethiopia, or Afghanistan. In one case, Campbell says, villagers objected to the seeds as being too large.
"In commercial production, such things wouldn't much matter," he says. "But if Mama is going to be cooking this material, it had better have the same look, taste, and color as what she's used to, or she won't accept it."
So Campbell's team distributed its new strains to breeders throughout research centers in Africa and Asia for hybridization with locally adapted, popular lines of the species. Unfortunately, he notes, 10 years later, these hybrids have yet to make it into farmers' hands.
During that decade, ICARDA's breeders were busy crossing strains of L. sativus with a low-neurotoxin Middle Eastern relative, Lathyrus ciliolatus, notes William Erskine, the institute's director of germ plasm research. Additional strains were developed by growing cells from various Ethiopian grass peas in tissue culture. As these cells multiplied, chromosomes were sometimes lost or pieces moved about, producing natural variants of the parent. ICARDA let the variants mature and then measured ODAP in thousands of them.
The best performers from these two ICARDA programs produce only about 0.04 percent ODAP but taste like the original plant.
A few farmers scattered throughout lathyrism-prone areas are already field-testing these new grass peas, notes John H. Dodds, the Washington, D.C.-based assistant director general of ICARDA. However, as a research center, his institute isn't in the business of producing and distributing large quantities of seed. That must be managed by others.
It also poses an unusual challenge, Dodds says.
Though growers around the world cultivate some 1.5 million hectares of conventional grass peas each year, most of their plots "are no more than 3 hectares [around 7.5 acres], and probably less than 1," he notes. Largely a subsistence crop, its growers don't tend to buy their seed but produce it themselves or receive it in barter with neighbors. No central distribution point disseminates new plants, and no institution is available to educate the million or so potential planters about varieties' advantages.
To cope with the problem, ICARDA has recently hired sociologists, anthropologists, economists, and other social scientists. Their mission is to work with officials in developing countries on establishing customized networks for the quick distribution of seed within the barter economies of small landholders.
However, Campbell hopes ICARDA won't stop there.
His own studies and those of legume researchers in many other developed countries indicate that planting grass peas may offer even relatively wealthy ranchers and prairie farmers a commercially attractive alternative to cereals, especially as a proteinaceous livestock feed or forage.
The protein content of grass peas runs about 28 percent, by weight--twice that of wheat. In his part of the northern Great Plains, Campbell can achieve grass-pea yields of 5,000 pounds per acre. That's comparable to field peas and three times the productivity of soybeans.
Moreover, when drought hits, nothing beats it, he says. "One year, we still got more than 1,000 lbs per acre despite just 2.5 inches of rainfall." By contrast, Campbell notes, "wheat came up just 4 inches high, then shriveled and died."
Even with what he perceives as the grass pea's great prospects for western rangelands, he concedes that convincing North American growers to try it will probably prove a tough sell. "Everybody is so hung up on this ODAP," he laments. "When we point out we got concentrations down to 0.01 percent, they ask why not zero."
Meanwhile, he notes, plenty of other commonly cultivated crops, such as broccoli, carry their own toxins, which similarly prove harmless when consumed in small amounts.
Indeed, Lambein told SCIENCE NEWS that he has found that the root of Korean ginseng (Panax ginseng) contains the same toxicant--ODAP--as L. sativus, "and at almost the same [natural] concentrations." Yet he hardly expects the finding to deter natural-products aficionados from downing Korean ginseng, which is prescribed by Chinese herbalists to overcome fatigue, weakness, premature aging, and stress.
"We live in a water-challenged world, one that is becoming more so each year as 80 million additional people stake their claims to the Earth's water resources," notes Lester R. Brown, an agricultural economist and chairman of the World-watch Institute in Washington, D.C. Each year, he notes, communities pump another 160 billion tons of water from underground aquifers for drinking, hygiene, industry, and food production.
Yet in the increasingly intense competition for water between these various sectors of the economy, irrigation for agriculture "almost always loses," he observes. Countries tend to offset the resulting loss in their food-production capacity by simply importing more grain from rain-fed croplands or areas with more-plentiful water resources.
Last year, he notes, the water required to produce the grain and foods imported into Ethiopia and other portions of parched North Africa "was roughly equal to the annual flow of the Nile River." However, if low-toxin L. sativus strains permit the expansion of grass peas throughout lands too dry to support grains, he says, they might offer a way to safely increase dryland food production.
Alternatively, he notes, the new, less-toxic grass peas might enable some farmers to plant a second, soil-nitrogen-replenishing crop during an otherwise dry, fallow season.
Still, Brown maintains, expanding the grass pea's range would only buy a little extra time. Ultimately, he argues, restoring the balance between water use and supplies will require reining in population growth, eliminating water waste, and shifting to more water-efficient technologies.
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|Date:||Jul 29, 2000|
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