A COMPARATIVE STUDY OF DIFFERENT METHODS OF DETERMINING ACTIVITIES OF GROWTH‐PROMOTING SUBSTANCES

PLANTS RESPOND to growth-promoting substances in a number of ways, but most of these responses are of such a nature that they are not readily measurable. However, during the last decade attempts have been made to utilize many of these responses to determine growth-promoting activities; while some of them are only qualitative, others are at least semiquantitative. There is no unanimity among investigators as to the accuracy or appropriateness of the various methods in general use; in fact, the situation is exactly the opposite. The reason for this disagreement, as the writer sees the situation, is partly due to prejudice and partly to the difference in viewpoint. One group has been mainly interested in discovering new chemical compounds which would elicit one or more of the many responses of plants to growth-promoting substances. These investigators have been for the most part interested in qualitative result, though they have also attempted to obtain some information as to relative activity of the different compounds. This group has used various plants grown under normal greenhouse conditions. Then there are those investigators who are interested in discovering the mechanism of the action of growth hormones on plants. The etiolated oat coleoptile grown under rigidly controlled conditions has been the main test object of this group, though etiolated pea seedlings have also been used to some extent. A third and more recent group of growth hormone investigators has in the main been attempting to determine the amount of hormone present in plants, and to associate this with growth habit, age, environment, etc. In other words this group has been interested in the application of the results of growth hormone studies to an understanding of the growth of plants. Several investigators (among them Zimmerman and Hitchcock, 1937; Thimann and Schneider, 1939; and Avery, Berger and Shalucha, 1942) have recognized the fact that different test methods give different results. To emphasize this fact further the writer decided to try out, in his laboratory, tests representative of all schools so that the results, all of which would be obtained by the same investigator under comparable conditions, could be more accurately compared than if done by several different investigators in different laboratories. The writer has had access to a number of new compounds which fact has made theinvestigation doubly interesting and worth while. METHODS AND MATERIAL.-After some preliminary experimentation it was decided to study stem curvature, epinasty, and gall formation in the to1 Received for publication March 25, 1943. Paper from the Department of Botany of the University of Michigan, no. 823. This investigation has been aided financially by the Horace H. Rackham Trust Fund of the University of Michigan. mato, the parthenocarpic development of fruits in the tomato, bud inhibition and enlargement (gall formation) of the cut stem of the sunflower, and curvature of the Avena coleoptile. The John Baer tomato was used throughout for the experiments on stem curvature, epinasty, and gall formation (enlargement of the stem at the point of application of the lanolin paste); the plants were grown in the greenhouse and were usually about 12 to 15 inches in height; careful choice as to size was made in each experiment. The parthenocarpic experiments were for the most part conducted in the field. The Russian mammoth sunflower grown in light was used throughout in the experiments on bud inhibition and gall formation, (Laibach, Mai, and Miiller, 1934). These plants were used when the first internode above the cotyledons was 3 to 4 centimeters long, except in some experiments where the influence of distance of application of the chemical was studied. Only plants with both cotyledons present and in good condition were chosen. The Victory oats, obtained from Batavia, New York, were used for the Avena experiments. The following chemicals were used: 2-fluoreneacetic (2-FIA), 4-fluoreneacetic (4-FIA), 9-fluoreneacetic (9-FlA), 7-acenaphthaleneacetic (7ANA), ,(-7-acenaphthalenepropionic (,/-7-ANP), diphenylacetic (DipA), 3, 4-dihydronaphthaleneacetic (3, 4-diHNA), 2-ethyl-1-naphthaleneacetic (2-ethNA), ,(-naphthoxyacetic (NOA),2 naphthaleneacetic (NA), naphthalenepropionic (NP), naphthalenebutyric (NB), indoleacetic (IA), indolepropionic (IP), indolebutyric (IB), phenylacetic (OA) acids, and naphthaleneacetamide (NAA). When applied to tomatoes or sunflowers, the chemicals were mixed with lanolin; in the experiments with Avena the chemicals were applied in the usual way in an agar block. The curvature and epinasty experiments with tomato plants were set up according to the method of Zimmierman and Hitchcock (1937), i.e. the lanolin paste was smeared on one side of the stem either in the second or third internode from the top; the position varied with each experiment, but in later experiments the second internode from the top was used. The experiments on bud inhibition and gall formation were carried out with young sunflower plants. As previously pointed out by the writer (1941a), the Russian sunflower rarely produces branches when intact, but will do so when the apical 2 The three fluoreneacetic acids, 7-ANA, ,B-7-ANP, 3,4-diHNA, 2-ethNA and NOA were supplied by Dr. John Sheehan of the Chemistry Department of the University of Michigan. The NOA was also supplied by Dr. P. W. Zimmerman of the Boyce Thompson Institute, Yonkers, N. Y. NAA, NP, and NB were supplied by the American Chemical Paint Co., Ambler, Pa. To all of these the writer wishes to express his appreciation.