Some Effects of Decapitation on Electrical and Elongation Phenomena in the Avena Coleoptile.

Growth of the Avena coleoptile, including elongation and curvature responses, is dependent on the auxin which is produced only by the cells in the extreme apex (4, 12, 13). A polar force is required to direct and control the distribution of this auxin. It frequently has been suggested that the inherent electrical field could function as this force and there is evidence that is consistent with this thesis (9). However, if the inherent electrical field is dependent on the auxin-regulated elongation process, then this hypothesis would be untenable. For this reason, it is important to test this possibility by experimentation. Preliminary evidence, from experiments which were not specifically designed to evaluate this point, indicates that the longitudinal electrical polarity of the Avena coleoptile is not directly dependent on the presence of auxin that is required for elongation (4, 14). It also has been demonstrated that a transverse electrical polarity, in response to mechanical and electrical stimulation, can be established in the etiolated oat seedling in which the auxin has been decreased by removal of the apex before stimulation (7, 10). However, no previous attempt has been made to measure simultaneously the elongation rate, as a manifestation of the functional auxin content, and the longitudinal electrical polarity of the Avena coleoptile. It is generally accepted that decapitation of the coleoptile removes the source of auxin and results in its gradual decrease in the remaining tissue, because auxin disappears in the process of growth (2). Since growth of the coleoptile is proportional to the amount of auxin added (2, 11, 13), it is permissible to use the rate of elongation as an index of the quantity of auxin used in this process. The present experiments were performed to determine the effects of decreased auxin supply resulting from decapitation, as measured by the elongation rate, on the longitudinal component of the electrical pattern of the coleoptile.