Effects of indoleacetic Acid on dictyosomes of apical and expanding cells of oat coleoptiles.

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.