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Effects of Indoleacetic Acid on Dictyosomes of Apical and Expanding Cells of Oat Coleoptiles ^1,2

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

We found that the auxin-induced growth is mediated through the activation of the dictyosomes (collectively, the Golgi apparatus). Incubation of oat (Avena sativa) coleoptile segments in indoleacetic acid-sucrose-phosphate buffer changes significantly the number of dictyosomes in the expanding cells. A further indication of auxin enhancement of dictyosome activity is a decrease in dictyosomal cisternae (flattened membranous sacs) number. This decrease occurred after 6 minutes of incubation in auxin, and then was followed by a reduction in the organelle number per se. These times are in keeping with the rapid action of auxin-induced cell elongaton, and the latent period of geotropism. In the apical cells, the effect of indoleacetic acid is more subtle and complex. The periods of increased dictyosome utilization and of increased dictyosome synthesis in auxin-treated segments alter with those of the control. These observations indicate that dictyosomes not only have a function in cell elongation, but also may participate in processes such as auxin transport and stimuli perception. The expanding cells have five times as many dictyosomes as the cells in the apex. Dictyosome number within a cell appears to be directly proportional to the length of the cell. The fluctuation of dictyosome number and the effect of auxin on the rate of elongation of individual outer epidermis are discussed.

¹ This work was supported by the United States Atomic Energy Commission, and Grant W12792 from the United States National Aeronautics and Space Administration.

² We dedicate this paper to Solon A. Gordon, who died October 5, 1973. Dr. Gordon devoted his career to the study of hormonal physiology. He and his life's work will remain with us a presence, more than a remembrance. We are grateful for his enthusiastic support, encouragement, and helpful discussion throughout this study.