Bold approach to gene engineering.

Although scientists are making rapid progress in the transfer of single genes into plant cells, most traits important to agriculture depend on the coordinated activity of a large set of genes, often with more than 100 members, says Robert J. Griesbach of USDA's Agricultural Research Service (ARS) in Beltsville, Md. Such traits include the ability to withstand high salt levels or drought periodsd or to coexist with nitrogen-fixing bacteria. Sometimes the genes behind a trail scattered throughout the plant's genetic material, but often they apppear to be clustered on a single chromosome. Griesbach has developed a technique to transfer a single chromosome, or a piece of a chromosome, into a foreign plant cell. He now reports the first evidence of expression of the genes transferred.

Griesbach uses a fine glass needle to inject a chromosome into a plant cell. Although scientists have been successfully injecting chromosomes into animal cells for five years, major obstacles have slowed the work on plants. First, the rigid cell wall has to be removed with enzymes, leaving a cell called a protoplast. Second, a method had to be developed to avoid puncturing the large strture, called the central vacuole, which contains toxic materials that can kill the cell.

Griesbach removes the vacuole by spinning the protoplast in a centrifuge. The vacuole contains oily chemicals, so it rises against the centrifugal force in the spinning protoplast and eventually is pinched off. When Griesbach, working with petunias, injects a chromosome into the remaining protoplast, about 25 percent of the protoplasts are capable of regenerating into full plants. In about a third of these cells the new chromosome is stably inherited when the cells divide, and Griesbach has evidence from 2-dimensional gel electrophoresis that the foreign genes direct production of proteins.