Transport of indoleacetic acid in intact roots of Phaseolus coccineus

Abstract

Indoleacetic acid (IAA)-5-³H (2×10^-9) was applied to intact roots of Phaseolus coccineus seedlings at the apex or 2 cm above the apex, and the movement of IAA-³H and its metabolites traced by sectioning and chromatography. Basipetal movement of label occurred for 2 cm or less, declining exponentially, and the amount increased with time. Acropetal transport from above the apex showed quantitatively less movement of radioactivity. After a 6h treatment period a decline of label occurred in the first 0.5cm, below which there was a long distance movement of small amounts of label, mainly in IAA, towards the apex where the label concentrated by a factor of approximately 2. Short-distance basipetal movement consisted of about equal amounts of IAA and metabolites, and only metabolites were found in areas more basipetal than 2cm. Label from solutions of sucrose-¹⁴C and ³H₂O followed the same general pattern of movement as label from IAA-³H, except that acropetal movement of water showed a steady decrease in the amount of label as the distance from the area of application increased. The short distance basipetal transport of label with the breakdown of IAA-³H indicates that the extent of basipetal movement was limited by catabolic processes. The acropetal pattern of IAA-³H movement with the concentration of the transported material close to the apex, is possibly the result of transport in the phloem.