Genetic engineers who want to improve cereal crops have a powerful new tool to speed their work. It's a technique developed to locate specific genes for specific traits in human DNA. Now an international research team is using the technique on barley, maize, oats, sorghum, rice, and wheat.
To team leader Pamela Ronald at the University of California's Davis campus, this is typical of what she calls the ''tremendous breakthroughs'' that have pepped up the science of crop-plant engineering in the last three years. Looking ahead in 1996, she says that ''things are changing very rapidly'' now in this science, which for many years had been developing fairly slowly.
The ultimate goal for plant geneticists like Professor Ronald is to so thoroughly understand the genetic blueprint of crop plants that they can redesign those plants to better meet human needs. They have to travel a long road from old-fashioned hit-or-miss plant breeding to reach the Star-Trek-like capacity to write a plant's genetic instructions in the laboratory.
Asked how far along that road they have come, Ronald explains that they have reached the point where they can work with natural genes. If scientists can find the genes they want in nature, they can manipulate them and insert them in crop plants. She says it will take ''more years'' to learn to actually synthesize desirable new genes. Yet given the accelerating rate of progress, she adds enthusiastically, ''We're on our way.''
Meanwhile, finding those useful natural genes in cereals defines the work of Ronald and her colleagues at Davis, as well as at the International Laboratory for Tropical Biotechnology at La Jolla, Calif., and the Academic Sinica in Beijing.
When the scientists reported on that research in the journal Science recently, news reports focused on the fact that they had used their new skill to give certain rice strains resistance to a bacterial blight. Ronald acknowledges that this is important because ''we now have improved rice plants.'' Yet putting her team's work in larger perspective, she explains: ''The big news is we have gotten [a powerful gene-hunting technique] to work in monocots.''
That's the class of plants to which cereals belong. Its name is botanists' shorthand for the term monocotyledon, meaning that the plants' embryos have only one seed leaf called a cotyledon. This is in contrast to the dicots whose embryos have two seed leaves.
Finding genes in monocots has not been easy. Genetic instructions which determine the form and function of an organism are encoded in the structure of DNA molecules. The molecule is built like a spiral staircase. Its sides are made of sugar and phosphate. Its ''steps'' are built of four kinds of molecules that chemists call bases - adenine (A), thymine (T), cytosine (C), and guanine (G). Genetic instructions are written in terms of this four-letter ''alphabet''; that is, according to the order in which the spiral staircase ''steps'' are arranged.
The DNA molecules themselves are coiled up in units called chromosomes. The trick to finding useful genes is to locate on a chromosome those bits of DNA that express themselves in useful traits. The international program to decode the human genome (genetic blueprint) has developed a battery of techniques for doing this. Ronald's team has adapted some of those techniques for use with monocot plants.
This opens the way for comprehensive genetic exploration of the major cereals. As Ko Shimamoto of Japan's Nara Institute of Science and Technology in Ikoma noted in a commentary in Science, rice has the smallest genome of major cereals. At the same time, the order of genes on its chromosomes generally parallels that of other cereals, making it a key research topic. ''Once genes with products of interest to agriculture are isolated in rice, counterparts in wheat, maize, and other cereals can be easily identified,'' Mr. Shimamoto said.
Ronald says this is why she expects that the gene-hunting tool her team has demonstrated in rice ''should help us make faster progress on engineering monocots'' generally.
Meanwhile, the pace of plant genetic engineering has picked up in many areas, as a few recently reported examples illustrate:
* At the University of Wisconsin at Madison, molecular biologist Richard Amasino and graduate student Susheng Gan spliced together naturally occurring genetic material to form a hybrid gene that slows or blocks senescence in plants. Dr. Amasino said last month that experimental ''tobacco plants with the gene weighed 50 percent more, had almost twice as many flowers and 50 percent greater seed yields than plants without the gene.'' The gene might also extend the shelf life of harvested vegetables.
* Entomologists at Australia's CSIRO laboratories in Canberra have given plant cells the genetic ability to produce a virus that kills pests in the cotton bollworm family. CSIRO senior research scientist Terry Hanzlik told a chemical congress in Honolulu last month that, because the virus attacks only the target insects, it is an environmentally safe means of pest control.
* Last October, plant biologists David Ho and Qing Xi Shen at Washington University in St. Louis reported that they have identified the genetic switch that turns on the ability of many plants to resist drought and other stresses. They say they now hope to produce strains of barley, wheat, and rice that have enhanced ability to turn on this switch.
''We could be on our way to making plants much more effective in response to stresses,'' Ho says.