Science: Busier Green Plants

For the first time in the history of science or agriculture, man may be about to make a fundamental improvement in the unique power of plants to manufacture food out of carbon dioxide and water in the presence of light. Selective breeding, long practised to increase the yield of plants, may eventually be looked back on as little better than superficial when compared with a new method described last week by Cornell’s Botanist Lewis Knudson. Using X-rays, Knudson has permanently increased the size of plants’ cnloroplasts—the cell’s tiny granular bodies where chlorophyll makes sugar and starch out of inorganic matter by the process of photosynthesis—most important chemical reaction in the world.

Botanist Knudson suspects that the bigger its chloroplasts, the bigger is a plant’s power to synthesize food for its own growth—and for the nourishment of man and beast. So Knudson’s colleagues are eagerly planning to adapt his method to develop more productive strains of corn, wheat, clover, other crops.

Though Knudson uses X-rays to modify plants, his results have no relation to those of other scientists who for 15 years have also been creating mutations of plants (and animals) with X-rays (TIME, April 14). Such previous mutations were caused by the ionizing—or “electrifying” —effect of X-rays on the cell’s chromosomes, kneading these heredity-determining units into unusual patterns and thus producing freakish plants which would seldom occur in nature.

Knudson’s X-rays produce their changes not by affecting the chromosomes, but rather the chloroplasts themselves. Reason: chloroplasts are passed on directly from parent plant to its offspring through the seed or spore instead of arising anew in each generation under the genetic influence of the chromosomes. Knudson worked with fern spores, because they are simple and sexlessly reproductive.

Some 80 of his thousands of X-rayed spores germinated with enlarged, disk-shaped* chloroplasts. Since this abnormality has persisted for almost ten years in his ferns, Knudson concludes that the chloroplasts of useful plants may also be enlarged for good, increasing their ability to perform the chemical reaction on which agriculture, and all life, is based.

* The disk-or lens-shaped chloroplasts of most plants are capable of a remarkable movement: when light is weak, they turn toward it their flat surface; when light is strong, they present only their edges. This tends to equalize their rate of photosynthesis.