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Rhythmicity in the Basipetal Transport of Indoleacetic Acid through Coleoptiles ¹

^a Division of Biological and Medical Research, Argonne National Laboratory, Argonne, Illinois 60439

¹⁴C-Indoleacetic acid was applied to coleoptiles of corn (Zea mays) and oat (Avena sativa). The coleoptiles were detached from the endosperms at 6-minute intervals after indoleacetic acid application, and the radioactivity was determined in successive 2-millimeter regions. The rate (per cent per minute) of basipetal transport of indoleacetic acid is periodic in various regions of the coleoptile, with a period of about 20 minutes. The possible relation of this cyclic phenomenon to other rhythmic processes of similar periodicities is discussed. A distinct acropetal transport (against the concentration gradient) from the subapical region to the apical 2-millimeter region of the coleoptile was detected.

The velocity of indoleacetic acid transport differs in different regions of the coleoptile. Within an entire coleoptile the velocity can be divided into three classes for corn, 41 millimeters per hour (apical), 13 millimeters per hour (mid), and 34 millimeters per hour (base), and 2 classes for oats, 28 millimeters per hour (apical) and 14 millimeters per hour (remainder). An inverse relationship between the velocity of indoleacetic acid transport, and the growth rate of the coleoptile is discussed. Corn coleoptiles exceed oat coleoptiles both in rate and in velocity of IAA transport.

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