Plant Hormones

In his botanical laboratory at the University of Chicago, Professor George Konrad Karl Link recently made a discovery which he considered so noteworthy that he sent a report of it all the way to England, where it was published in the issue of Nature which came back to the U. S. last week. Dr. Link had found a plant hormone called heteroauxin, previously found elsewhere, in the nodules of red kidney beans. When applied to the bean roots, a paste containing the hormone caused bending, coiling, vertical retardation of root growth, lateral acceleration of root growth, local increase in thickness of the root.

This report followed closely after another from Dr. Link having to do with crown gall, a local infection of apple trees which superficially at least resembles cancer in animals. Crown gall and cancer are both proliferations of unhealthy cells. Botanists have long known that the gall is caused by a bacterium, Phytemonas tumefaciens. Dr. Link succeeded in inducing galls by application of heteroauxin, keeping the bacterium away from the scene of operation.

These reports were welcomed by plant physiologists as two more interesting contributions to the important and already broadly extended research into what makes vegetation grow. It is estimated that one ounce of active plant hormone would stimulate enough vegetation to girdle the earth at the equator. Researchers can now detect the effect on one plant of one ten-billionth of a gram of hormone. No subject has excited plant physiologists more than this in the past decade, and it has seen its major development in the last five years. Yet it was foreshadowed a half century ago by Julius von Sachs, a brilliant German who reasoned that roots and flowers must be produced by special chemical substances, root-forming and flower-forming, elaborated in plant tissue. The foundations of the science were laid about 1910 by Fitting of Germany, and by Boysen Jensen of Denmark. The latter cut off the tip of the leafsheaves in young oats. This stopped the stalk from bending toward light. When Boysen Jensen glued the tip back on, the stalk started bending again, although only the tip was exposed to light. This indicated that some light-sensitive something was dribbling down into the stalk from the tip across the wound gap. The fact that a special substance, instead of a vague irritant, was involved was first clearly demonstrated by Paal of Hungary. In 1925 Seubert of Germany found plant-stimulating substances outside of plants--in saliva, pepsin, malt extract, diastase. These substances were christened "auxins" by Koegl of Holland's Utrecht University, where much of the pioneer work on them was done. In 1928 a tall, dark young man named Fritz Warmolt Went, who began his botanical career at Utrecht under the tutelage of a distinguished father, got enough of one auxin in high concentration to measure its molecular weight. Three years later Koegl and his associates identified an auxin in urine, isolated it in pure form. This is called Auxin A. In 1934 the Utrecht researchers followed with Auxin B and heteroauxin. Heteroauxin has the astonishing effect of making roots sprout from the stem in shaggy masses like beards. It also produces elongation and swelling in stems, stimulates normal root formation, inhibits buds.

Meanwhile at the Boyce Thompson Institute for Plant Research investigators had been observing the effect on plants of certain gases such as ethylene, acetylene, carbon monoxide. These effects in some ways were similar to those produced by the plant hormones. Eastman Kodak Co. was selling a near chemical kin of heteroauxin--indole-3n-propionic acid. The Boyce Thompson chemist thought he might be able to convert one to the other. Before he started, however, Drs. P. W. Zimmerman and A. E. Hitchcock tried out the indole-3n-propionic acid itself. To their unbounded delight, it produced nearly the same phenomena as a plant hormone. Promptly they began experiments with some 30 other likely sub-stances--not hormones--such as naphthalene acids and indole derivatives. About half of these disclosed some form of hormonic activity.

In this instance, the lag of commercial exploitation behind laboratory research was remarkably short. Indolebutyric acid, one of the Boyce Thompson stimulants, has already been placed on the market by several manufacturers as a root stimulator for cuttings. Merck Chemical Co. sells it as "Hormodin A" at a price of $2 for 15 cubic centimetres, which, diluted upwards of 6,000 times, is enough for about 1,500 cuttings. Pennsylvania Chemical Corp. markets it under the name of "Auxilin" at a price of $1 per half ounce. The prospect is that in ten years the nurseryman who neglects to stimulate his cuttings with root activators will be as old-fashioned as a railroad with wood-burning locomotives.

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