INFLUENCE OF INDOLE‐3‐ACETIC ACID ON THE RESPIRATION AND GROWTH OF INTACT WHEAT SEEDLINGS

INVESTIGATION OF the influence of auxins on different phvsiological processes constitutes an important, but as yet relatively unexplored, aspect of plant hormone research. Although the ultimate effect of auxins is usually measured in terms of cell or organ enlargement, little is known regarding the mechanism by which the final result is attained. Accelerated respiration might be expected to accompanv increased growth, especially if this involves cell multiplication and increase in protoplasm in addition to mere enlargement of cells. Several investigators, however, have failed to detect any accelerating influence of auxin on respiration; they noted retardation when high concentrations were employed (BoysenJensen and Nielsen, 1925; Bonner, 1936; 2 Kogl, Haagen-Smit, and van Hulsen, 1936). Calculations led Thimann and Bonner (1933) to conclude that auxins do not enter directly into the growth reactions of the Avena coleoptile but "act in some indirect manner that allows each molecule to exert its influence a number of times." The coleoptile of grass seedlings is an ephemeral structure with relatively low metabolic activity. In an attempt to discover the influence of auxins on metabolic processes of plants, it seems of interest, therefore, to investigate organs that are physiologic,ally more active. The present experiments were performed in order to study the effect of indole-3-acetic acid, or heteroauxin, on the respiration and early growth of intact wheat seedlings. The work was done in the laboratory of plant physiology of Columbia Iniversity. The friendly and helpful criticism of Prof. Sam F. Trelease is appreciatively acknowledged. MATERIALS AND METHODS.-Fresh solutions of crystalline indole-3-acetic acid (Eastman Kodak Co.) were prepared for each experiment by dissolving a suitable quantity in 1-'2 cc. of 95 per cent ethyl alcohol and then diluting with water distilled from Pyrex flasks through quartz condensers.3 The stock solution was heated to evaporate the alcohol. Similar quantities of alcohol were added to the water to be used in control tests and were evaporated in the same way.