The movement of 2,4-dichlorophenoxy acetic acid in root segments of Pisum sativum L. : II. Immobilisation and oscillations in uptake and transport.

An acropetal polarisation of the movement of 2,4-dichlorophenoxy acetic acid (2,4-D) through subapical segments of Pisum seedling primary roots has been monitored throughout a 60 h transport period in darkness at 25° C using [1-(14)C]2,4-D and [2-(14)C]2,4-D. Uptake of 2,4-D does not proceed at a constant rate; periods in which the amount of (14)C in the root segments and receiver blocks increases rapidly are followed by periods in which the amount of radioactivity remains relatively constant or declines slightly. These oscillations do not appear to be related to the time of day at which the experiments are begun or ended. Immobilisation and degradation of 2,4-D during transport in the segments seems to be low. Replacement of [1-(14)C]2,4-D donor blocks after 25 h by blocks containing unlabelled 2,4-D results in continued transport of the compound into receiver blocks, with only small amounts of (14)C remaining in the root tissues. Radioactivity is also exported from the segments into the blocks used to replace the donor blocks, with larger amounts being exported into the blocks applied to the apical ends than into those applied to the basal ends of the segments. This radioactivity may be taken-up again by the segments but more (14)C is exported into these blocks towards the end of the experiments. The possibility of regular oscillations in uptake and movement of 2,4-D in Pisum root segments is discussed.