LACK OF INHIBITION OF LATERAL BUDS BY THE GROWTH-PROMOTING SUBSTANCE PHENYLACETIC ACID

Abstract

It is now a well-known fact that indole acetic and indole butyric acids, when applied in lanolin to cut apices of stems suppress the formation of lateral buds, as do the terminal buds themselves. Thimann and Skoog (9) were the first to demonstrate this when they applied an extract from Rhizopus suinus to decapitated Vicia faba seedlings and found that the lateral buds were inhibited. It was later found that the active substance was indole acetic acid. Since that time other investigators have demonstrated the same thing for other plants (2, 3, 6, 7, 8, 9,10). In some laboratory experiments with Helianthus annuus the writer applied indole acetic acid and phenylacetic acids in lanolin to the cut surfaces of stems. After some time it was noticed that some of the treated plants had produced lateral buds while others had not and when a check was made it was found that the treated plants that produced shoots were the ones that had been treated with phenylacetic acid. This interesting observation led to a more detailed and carefully controlled experiment. Helianthus annuus was used again because under normal treatment it never produces any lateral buds or branches. Four lots of 16 plants each were carefully selected, besides some control plants not decapitated. These plants were between 60 and 70 centimeters tall; no flower buds had as yet been formed. Ten to 15 cm. of the top were cut off from each one of these 64 plants. The cut was always about one centimeter above a node. One per cent, indole acetic, indole butyric, and phenylacetic acids mixed separately in lanolin, as well as lanolin alone, were used. Sixteen plants were treated with each chemical on March 20, 1939. A considerable amount of material was smeared on the freshly cut surface, but it was not repeated during the time of the experiment. On April 10 representative plants from each group were photographed (fig. 1). At that time the plants treated with the auxin showed the typical gall formation, but no buds or lateral shoots had been formed on any of the plants treated with indole acetic and butyric acids. The plants treated with phenylacetic acid had on the other hand formed as many and nearly as large buds as the plants treated with plain lanolin. A month later (May 13) representative plants from each lot were again photographed (fig. 2). As the photograph shows, all of the plants except those not decapitated had by now produced some buds or branches. It is to be remembered that during a period of 54 days no new auxin application had been made. By