Auxin transport in roots of young pea seedlings.

The effect of root and shoot apices and their replacement with IAA (Indolyl-Acetic-Acid) on the development of cambium in pea roots was studied. The movement of IAA in intact seedlings was studied by treating the seedlings on either the root or shoot apex end with IAA-C14, and counting the radioactivity in the extracts from the treated tissues after a certain period. The movement and fate of externally applied IAA-C14 was studied by means of a paper chromatogram scanning technique. The distribution of IAA in different segments of the seedlings was studied by preparing micro-autoradiographs. The data found suggested that IAA coming down from the shoot apex initiates cambial activity in the roots. An upward movement of IAA from the root apex is absent. The undetectability of an upward movement of auxin from the root is not due to the presence of a predominantly strong basipetal movement of IAA from the shoot apex. Movement of IAA in intact seedlings was mainly basipetal but a little radioactivity derived from IAA was found to be transported acropetally as well, i.e. towards the shoot base. This was mainly through the xylem tissues. When IAA was applied to the cut shoot apex end of the seedling, IAA was found to be present in all the living tissues and comparatively less in the xylem. When IAA was applied to the cut shoot apex end, it was found to remain in its original chemical form in the shoot and the upper part of the root; but when IAA was applied on the cut root (iv) apex end it was found to break down into at least three compounds in the root segments. The literature related to the experiments is reviewed and the results of the present investigations are discussed.