Acropetal Auxin Transport and Xylem Regeneration-A Quantitative Study

Abstract

Earlier experiments on the polarity of auxin-transport in shoots are critically discussed. The following points are emphasized: The importance of short-time experiments; the value of using physiological auxin-concentrations; the need for relating transport data to normal physiological processes; and, in particular, the necessity of guaranteeing that no movement of auxin is occurring in a surface film of water. Previous research on the relation between auxin and xylem regeneration in vegetative Coleus shoots has been extended and quantified. Evidence is presented that: 1. In young No. 2 internodes the ratio of basipetal to acropetal auxin-transport is 3 : 1, when physiological auxin concentrations are used. 2. The amount of xylem regenerated when a vascular strand is severed is limited by the amount of auxin which can reach the regenerating area from the leaves. 3. The amount of auxin which can reach the regenerating area is, in turn, normally limited by the transport-capacity of the internode.