New `green revolution'? Not yet
NEWS reports already call it the second ``green revolution.'' A National Academy of Sciences report proclaims, ``What scientists will now be able to accomplish through the use of molecular genetic techniques [in agriculture] is awesome.'' But to biologists working on this promising frontier, it's the basic unknowns that seem awesome right now. Corn that makes its own nitrogen fertilizer, extra-nutritious rice, and superwheat that resists all pests are still on wish lists. Only relatively simple improvements, such as making soybeans resistant to herbicides, seem imminent.
Agriculture's long-term future, however, may depend on the success of genetic engineers. The academy has also warned that the genetic diversity of many crops is dangerously narrow. The fact that the entire South American 1984 banana crop depended on a single variety may be an extreme example. But breeding for production of food, oil, and fiber has brought a genetic uniformity in many crop species, weakening their ability to adapt to changes in pests and weather.
Traditional crop breeders can only shuffle the plant's genes themselves, using a shrinking reservoir of wild varieties to renew genetic vigor. The molecular botanists will be able to search far more widely for the genetic material they need. And, if nature doesn't provide it, they may even be able to synthesize it themselves.
Plants are far more complicated than the simple bacteria that genetic-engineering techniques have focused on. Few traits important to the world's food crops depend on single genes. Most are governed by assemblies of genes, such as the 17-gene group involved in fixing nitrogen fertilizer from the air. Scientists are only beginning to discover how this complexity works. They are also only beginning to develop the tools they need to deal with it.
Molecular tinkerers have had considerable success sneaking genes into many plants with the help of Agrobacterium tumefaciens. This bacterium, which naturally infects these plants, carries a tiny ring of DNA called the Ti plasmid. Engineers replace a bit of the plasmid with the gene they want to transfer. The plasmid then smuggles this gene into cells of the plant.
This works best with peas, beans, and other broad-leafed plants (dicots). Narrow-leafed, grass-type plants (monocots), which include the major cereals, aren't easily infected by the plasmid. So the green engineers are looking for other means to smuggle in their genes.
Virginia Walcot of Stanford University announced an important technical breakthrough last March when she showed how to use a kind of electric shock treatment to get monocot cells to take up foreign DNA. The cells open up temporary holes in their walls through which the DNA can slip. Although biologists have known about this effect for a decade, Dr. Walcot has made it into a practical tool for genetic engineers.
Other researchers treat monocot cells with polyethylene glycol to induce them to take up foreign DNA. In Japan, for example, scientists at the University of Tsukuba have slipped a gene for antibiotic resistance into rice with this technique.
Redesigning cells is only part of the work. To be useful agriculturally, those cells have to grow into whole plants. So far, such cell culture is hit or miss. But there are some successes. In Japan, at Kyoto University and in laboratories of the Mitsubishi and Mitsui Toatsu industrial groups, research teams have produced whole plants from rice cells. At Cornell University, corn plants grown by tissue culture are thriving. And in Champaign, Ill., United Agriseeds Inc. reported that two years of research has enabled its scientists to grow seed-bearing soybean plants by tissue culture.
While such results encourage plant geneticists, they still have a great barrier between them and a genetically engineered agricultural revolution -- the barrier of their own ignorance. There is no well-established theory to guide their efforts to grow viable plants from cells. It's done by trial and error. They know only a few of the genes and gene complexes that are important to crop-plant properties. They still don't know how plant genes work or even what turns their functions on and off.
Walcot notes that, while her method allows foreign genes to enter corn cells, no one understands how those genes become effective. Only about 1 to 2 percent of the treated cells actually gained new genetic material.
Some plant traits, such as herbicide resistance, stem from single genes and are more easily handled. Ciba-Geigy Corporation is growing 8,000 tobacco plants that were given herbicide resistance. The experiment is a prelude to efforts to confer this resistance on soybeans. That would allow farmers to use weed killers without harming this valuable crop plant. Monsanto Company is following similar research.