SCIENCE/TECHNOLOGY
Herbicide-Resistant Crops Focus of Biotechnology Debate policy researcher who organized the symposium. Two conflicting views of modern agriculture exist, according to Roger Wrubel, a professor of urban and environmental policy at Tufts. One view holds that agriculture is an essentially healthy endeavor, and such problems that do currently exist are amenable to technological solutions. An essential component of that technoloRudy M. Baum, gy, in this view, is biotechnology. The C&EN West Coast Bureau opposing view is that agriculture as it is currently practiced is environmentally unvery step forward in the biotechtenable, and that biotechnology is simply nology revolution has stirred deanother in a long line of technological fixbate, perhaps none so impases that will only delay a necessary shift in sioned as the issue of introducing genetperspective by farmers. ically engineered organisms into the environment. As a class of genetically Those two views are particularly apengineered plants—one tolerant to parent with regard to genetically engichemical herbicides—moves toward neered herbicide-resistant crops, Wrubel widespread commercial use in the next notes. Biotechnology proponents argue few years, the debate has sharpened, as that herbicide resistance can be environwas evidenced by exchanges at a session mentally beneficial. If a crop can be on agricultural biotechnology at the anmade tolerant to an herbicide with good nual meeting of the American Associaenvironmental characteristics, then such tion for the Advancement of Science herbicides can replace others that do held recently in Boston. more damage to the environment. Additionally, on crops that currently are treatResistance to herbicides is only the ed with multiple herbicides, resistance to first of numerous traits researchers are a single broad-spectrum introducing into crop plants by herbicide could allow a derecombinant DNA techniques. crease in the total amount of Efforts are under way to create herbicide required to grow plants that produce their own the crop. pesticides, that are more resistant to disease, frost, or The opposing view, Wrudrought, and that contain more bel points out, maintains starch or a different mix of prothat agricultural chemicals, teins. Scientists, activists, and like herbicides, fall into two regulators are grappling with categories: ones that have the many issues surrounding been proven to be harmful the introduction of such genetto the environment and/or ically engineered plants into human health; and all the widespread agricultural use other ones, which are also and the foods these plants harmful, even though scienyield to the marketplace. tists have not yet shown why. As such, anything that Supporters of these efforts allows an increase in the maintain that biotechnology is the next logical and essential step Monsanto researchers have genetically modified canola plants use of agricultural chemithat will give farmers the tools in left andrightrows to be resistant to the company's Roundup cals, like genetically engineered herbicide tolerance, they need to feed a burgeoning herbicide. Canola plants in the middle row have not been altered should be discouraged. world population. to resist herbicide
• Arguments reflect conflict in modern agriculture as introduction of genetically engineered crops approaches
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MARCH 8, 1993 C&EN
Opponents fall into two categories, as they have since the dawn of the age of recombinant DNA in the early 1970s. In the one camp are scientists and activists who argue that genetically engineered plants, animals, and microorganisms pose more significant environmental and human health risks than the boosters of biotechnology are willing to acknowledge. These opponents insist that stringent regulatory safeguards are needed to prevent future catastrophes. In the other camp are those opponents who maintain that manipulating the genetics of organisms amounts to "playing God" and is morally wrong. Not surprisingly, these opponents would like most commercial applications of genetic engineering halted. All three views were represented at the AAAS meeting. Although agricultural biotechnology represents only one element of the commercial application of genetic engineering, "about 90% of the media attention and public concern has been directed at this aspect of biotechnology," observed Sheldon Krimsky, the Tufts University
Agricultural biotechnology firms are moving aggressively to develop herbi cide-resistant crops, Wrubel notes. Through the beginning of 1993, 120 per mits had been granted by the U.S. Depart ment of Agriculture for conducting field tests of plants that had been genetically engineered to be resistant to an herbicide. For the same period, a total of 350 permits for field tests of genetically engineered plants were granted by USDA. This emphasis is not surprising, Wrubel says. Herbicides are much more heavily used in the US. than either insecticides or fungicides, with about $3.5 billion per year spent on herbicides. Another speaker at the symposium, Stephen O. Duke of USDA's Southern Weed Science Labora tory, Stoneville, Miss., pointed out that, in developed countries, herbicides represent 70 to 80% of the total amount of pesticides used on crops. Two speakers at the symposium well represented the gulf that exists between proponents and opponents of agricultur al biotechnology in general and its appli cation to development of herbicidetolerant plants in particular. Robert T. Fraley, of the new product division of Monsanto, is an ardent supporter of the potential of biotechnology to improve agricultural productivity worldwide. Jane F. Rissler, of the National Wildlife Federation's Biotechnology Policy Cen ter, dismisses herbicide tolerance as a technology that is "deeply embedded in a chemical quick-fix mentality." In his presentation, Fraley pointed out that during the past 50 years the cost of food for U.S. consumers dropped 24%, with Americans spending about 14% of their disposable income on food, com pared with a world average of 25%. In that same period, agricultural productiv ity in the U.S. climbed threefold because of new fertilizers, equipment, farm man agement practices, and herbicides. "New technology has been a key contributor to gains made in agricultural productivity/' Fraley says. Monsanto scientists have played a key role in developing techniques for the ge netic engineering of plants, Fraley ob serves. Research at companies like Mon santo and at universities now makes it possible to engineer virtually every com mercially important plant, from grasses, to trees, to legumes, Fraley says. Monsanto's interest in herbicidetolerant crops stems from the company's popular broad-spectrum herbicide, Round-up, the active ingredient of which
Plants are being engineered to resist numerous herbicides Herbicide
Atrazine (triazine)
Physiological effect
Structure
CI
Inhibits photosynthetic electron transport (CH3)2HCHN
Bromoxynil
Chlorosulfuron (sulfonylurea)
Imazapyr (imidazolinone)
Ν
NHC2H5
Inhibits photosynthetic electron transport
Inhibits branchedchain amino acid biosynthesis
Cl Ο Ο , CH 3 /=( Il II N=\ — S — N— C—N—( x Ν
\-^
ΙI
ΙI
O H
Il
H
Inhibits branchedchain amino acid biosynthesis
W
CH(CH3)2 HN-^
Glyphosate
Λ NΙ-?
Inhibits aromatic amino acid bio synthesis
CH3
HO—P—CH2NHCH2COOH
I
OH
Glufosinate
Inhibits glutamine biosynthesis
O
NH2
Il
I
H 3 C—P—CH 2 —CH 2 —CHCOOH
I
OH COOCH3 Diclofop (aryloxyphenoxypropanoate)
Inhibits lipid biosynthesis
Sethoxydim (cyclohexanedione)
Inhibits lipid biosynthesis
Cl
V V - n - A V - O—CH n_ I Cl
CH, "•3
CH,
|
H5C2SHCH2C" ^ "
||
"C 3 H 7 "OH
Source: Stephen O. Duke, U.S. Department of Agriculture
is the compound glyphosate, or N-(phosphonomethyDglycine. Glyphosate blocks the activity of an enzyme, 5-enolpyruvyl-shikimate 3-phosphate synthase (EPSP synthase), that is in volved in aromatic amino acid biosyn thesis and that is produced only by green plants. As such, glyphosate is ex tremely toxic to all green plants and al most nontoxic to other living organ isms. Round-up is generally used as a "preemergence" herbicide: Farmers use it to clear a field of weeds before a crop
sprouts. Monsanto and other agricultur al biotechnology companies are devel oping plants with resistance to glypho sate so that the herbicide can be used more widely as a "postemergence" agent. There are numerous economic and environmental advantages to postemergence herbicide application. Two approaches have been used to produce such plants. Because glyphosate blocks EPSP synthase, additional copies of the EPSP synthase gene have been in corporated into plant genomes to pro vide those plants with the ability to proMARCH 8,1993 C&EN 39
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MARCH 8, 1993 C&EN
SCIENCE/TECHNOLOGY
duce more of the enzyme. Alternatively, because plants cannot naturally degrade glyphosate, efforts have been made to incorporate into plants microbial genes that encode enzymes that break down the herbicide. Both approaches have proved successful, Fraley says, and within two to three years, the first glyphosate-resistant crops—soybean, cot ton, and canola—will be on the market. Although farmers will pay more for herbicide-tolerant plant seeds, Fraley notes, they will pay much less for the herbicides used to control the weeds in a field planted with such an herbicide-tol erant crop. Weed control in soybeans, he adds, now costs farmers about $18 per acre. By contrast, the use of glyphosate on glyphosate-resistant soybeans would cost about $6.00 per acre, he claims. Rissler, on the other hand, who says she approaches the discussion of herbi cide-tolerant crops as "a feminist and an environmentalist/' maintains that it is "ridiculous" to "talk about whether glyphosate is better than paraquat or 2-4-D" for the environment. Modern herbicides like glyphosate and the sul fonylureas "are not environmentally friendly,,, Rissler insists, because they are highly toxic to plants. Rissler argues that modern agricul ture is a product of a mechanistic or re ductionist worldview that holds that plants and animals can be, intellectual ly, broken into their constituent parts and reassembled into something that has been improved. Embedded in the debate over herbicide-tolerant crops are the claims that such crops can con tribute to the conversion to sustainable agriculture and a shift to environmen tally friendly herbicides, Rissler says. Neither claim is true, she maintains. Truly sustainable agriculture must grow out of a "holistic worldview, which sees the whole as more than the sum of its parts," Rissler says. It must embrace ecology and focus on the con nections among all living organisms. Such a worldview "offers the possibility of a new relationship between humans and nonhuman nature," she adds. Agricultural biotechnology embod ied by herbicide-tolerant crops "pro motes business as usual," Rissler says. "It will allow farmers to continue cur rent practices without changing their mind-set, their worldview, to a truly sustainable agriculture. We've been down this route before with DDT and other agricultural chemicals."
Rissler's presentation provoked an intriguing exchange later during the session. Florence M. Wambugu, a plant pathologist with the Kenyan Agricultural Research Institute who is now working at Monsanto in an effort to develop virus-resistant sweet potatoes through genetic engineering, pointed out that in Africa, women are responsible for the majority of agricultural labor. African women working in the fields spend as much as 60% of their time pulling weeds, Wambugu added, suggesting that it was disingenuous for Rissler to state that feminists should oppose herbicide-resistant crops. "Agricultural problems in Africa are due to a lack of intensive agricultural development, a lack of inputs, and a lack of knowledge," Wambugu says. "We need to transfer agricultural technology from the U.S. and Europe to improve our food production." Wambugu's work at Monsanto on sweet potatoes, which is being funded by a grant by the U.S. Agency for International Development and Monsanto, will help improve the sturdiness of one of the major Third World food crops. It will also, Wambugu says, provide her with knowledge she can transfer to other African scientists upon her return to Kenya. USDA's Duke puts the issue of herbicide-resistant crops into some perspective. Herbicide-resistant crops will have to compete with other options a farmer has for weed control and will not eliminate a farmer's options, as activists like Rissler suggest, he says. And herbicidetolerant crops face obstacles other than the antipathy of environmental activists, Duke points out. There are questions about whether the public will accept genetically engineered food, about the rise of herbicide tolerance in weed species, and about pleiotropic effects such as reduced yield accompanying herbicide tolerance. Herbicide-resistant crops are unlikely to have much effect on the total acreage treated with herbicides, Duke says, because most agricultural land already is treated with herbicides. They are, however, likely to reduce the total volume of herbicides used. Although such crops will improve the efficiency of reduced-tillage agriculture, they are also likely to accelerate the evolution of herbicide-resistant weeds. Ironically, herbicide-resistant crops are likely to be a tool in managing such resistance, Duke concludes. •
Catalysis facilitates oil refinery changes The "oil refinery of the future" is here now. Environmental regulation has made it necessary, technical and economic conditions notwithstanding. As regulations become more restrictive and prescriptive, the oil refiners of the past, the so-called oil boilers, are converting their refineries into the largest chemical plants in the world. The Netherlands has been in the forefront of this changeover, and some insights from the Dutch perspective come from Jeop E. Naber, director of process research and Ian E. Maxwell, catalytic research and development manager for Shell Research B.V. Both are industry consultants to the Netherlands new Institute for Catalysis Research (C&EN, March 1, page 27). Catalysis is a key discipline in the modification of processes and the development of new ones to make environ-
Looking
mentally acceptable fuels. Conversion of crude oil is expected to remain the principal source of motor fuels for many years, but production of fuel additives in large quantities along with conversion of natural gas will become significant. The various oil crises arising from political problems in the Middle East during the past 20 years provided the push to convert more crude oil to motor fuels. This usually has been accomplished, at least in Dutch refineries, through catalytic cracking and flexicoking, a process for gasifying high-sulfur coke. Although bottom-of-the-barrel upgrading has helped to minimize the effects of higher crude prices, it has also given birth to a new petrochemical processing industry. In particular, the upgrading has meant increased attention to top-of-the-barrel technology. The lighter, C, to C4 components have become important feedstocks. Using these feedstocks, though, means increasing their molecular weights through such processes as oligomerization and paraffin alkylation.
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