Morphactin transport and metabolism in tree bark tissues: comparative studies in vitro

Abstract

AbstractBark banding of morphaction is an effective means of controling stem elongation in Pinus radiata D. Don (Monterey pine) but not Juglans regia L. (English walnut). Diffusion coefficients of 14C‐labeled morphactin across excised disks of tree bark, measured in specially designed diffusion chambers, were 11 to 85 fold greater in pine than walnut. In seedlings of comparable age, the suberin layer of walnut bark is much thicker than that of pine; if the layer is removed, diffusion of 14C‐morphactin is enhanced 39‐fold in pine and 285‐fold in walnut.Morphactin applied to the bark as an ester is rapidly hydrolyzed to its carboxylic acid derivative in both pine and walnut. This conversion occurs rapidly in the bark of both species and does not appear to limit the rate of morphactin movement across the bark.These results suggest that diffusion across the suberin layer and not metabolism limits morphactin transport across the bark.