Radioautographic analysis of the distribution of label from h-indoleacetic Acid supplied to isolated coleus internodes.

Isolated fifth internodes of Coleus blumei Benth. were supplied with (3)H-IAA at their apical ends. Microradioautography, using thin sections (0.25-0.5 microns) of Epon embedded tissue and liquid emulsion techniques, revealed extremely specific localization of the acetone-insoluble derivatives of IAA. Changes in the patterns of labeling were followed over periods of 3, 24, and 48 hr at various distances from the source of applied auxin. Progressively basipetal labeling of the cell walls of the youngest xylem elements was evident with time. At the end of 24 hr the label was detected also within the cytoplasm or slime of phloem elements. After 24 to 48 hr, labeling of plastids was evident. The results suggest a continued incorporation of IAA derivatives into cell wall precursors.