Science: Toward Control of Growth

Amid the gently rolling countryside of Beltsville, Md., there is a strange garden that would drive any weekend horticulturist to distraction. Among the odd sights: pine trees that grow only 8 in. tall, chrysanthemums that flower in spring instead of fall, poinsettias that bloom in June’s heat instead of Christmastime cold. But these plant anomalies are manmade. For U.S. Department of Agriculture scientists have discovered the mysterious chemical in plants that regulates plant growth, have found that they can stunt trees at their pleasure, make flowers bloom when they choose.

Light in the Darkness. Nurserymen have known since 1920 that certain plants could be made to bloom earlier than usual by shading them with opaque cloth for part of each day. Guess was that something in the plant’s internal mechanism recorded the smaller amount of sunlight, signaled the plant that the days had shortened, that colder weather was approaching, and that it had better flower fast. But botanists were unable to identify the day-measuring mechanism or explain how it worked.

To study this mechanism, Beltsville scientists under Dr. Sterling B. Hendricks, 60, first played all the colors of the spectrum on a variety of plants. Most colors had no effect. But when red light was played on the plants, the effect was dramatic. They reacted even to a brief, 30-sec. flash of red light during a 14-hour period of darkness. Apparently programed to the proposition that a new day had begun, the plants altered growth cycles accordingly.

Having learned that red light was the key, the scientists squeezed the juice out of bean seedlings, separated the juices into many different fractions, and tested each for its reaction to red light. Their quarry proved to be a protein-containing pigment that makes up only one part in one million of the juice.

Change in the Morning. In a way that scientists still do not fully comprehend, the pigment changes its chemical structure when red light hits it. As long as the red light lasts, the new structure persists. When the light dies, the pigment begins slowly to change back to its original state, a process that takes roughly twelve hours. Thus, when the red rays in the morning sun strike a leaf, the light-sensitive pigment changes into its new state and stays that way until sundown. This tells the plant, in the chemical language to which it responds, how long the day is and therefore what the season is,

To check their findings, Beltsville’s men dosed plants with red light at all hours of the night. Fooling plants into believing the nights were longer or shorter than they really were seasonally, the scientists were able to make plants bloom months early or late. They have so efficiently programed some pine trees that they grew only 8 in. in four years—responding to the signal that it is winter, no time for growth—while their unmolested neighbors rose to 20 ft.

The Beltsville substance is so new to chemists that it has not yet been analyzed or even named. But it is a major discovery in basic knowledge, may lead to bigger crops grown faster, and to control over harvesting times. “It’s as if we had been hitting a carburetor with a hammer for years in an attempt to adjust it,” says Dr. Hendricks. “Discovering this pigment is like learning that a screw on the bottom of the carburetor is what regulates it.”