Mesquite Root Inhibition Tests to Study Inhibitory Activity, Absorption and Translocation of 2,4-D and 2,4,5-T

Abstract

mrHE technique used in the tests herein reported is based on the T inhibition of root elongation by growth substances, an exceedingly sensitive response. Two procedures are used in the application of the growth substances. The first consists of applying known amounts of test compounds to the root bathing solution of mesquite seedlings, and the second procedure consists of applying these compounds to the cotyledons. After addition of the growth regulator to the solution subsequent root inhibition is dependent on absorption by the root tissue and accumulation in an active form at the site of action. In cotyledonary applications, translocation as well as absorption is necessary before inhibition of root elongation will occur. It was the objective of this study to investigate various possibilities for using these procedures in herbicide absorption and translocation experiments. The use of root inhibition as a quantitative test for growth hormones was suggested by Lane (13) in 1936. The inhibition of Avena root elongation was employed by Bonner and Koepfli (5) in obtaining dosage response curves suitable for making quantitative estimates of indoleacetic acid (IAA). Thereafter, extensive use was made of this response in studying the action and activity of growth substances. Reviews by Aberg (1), Burstrom (6), and Torrey (18) summarize most of the root inhibition experiments, criticize the technique and discuss the significant findings. In most root inhibition experiments, the compounds have been added to the root bathing medium. However, IAA applications to stumps of shoots (17) and the endosperm (5) of Avena were found to retard root growth. On the other hand, similar applications to Pisum and Zea mays (17) failed to inhibit root development. Crafts (7) reported that measurements of root injury could not be obtained when small dosages of 2,4-D were applied to cotton leaves though large doses killed the roots. Van Overbeek (19) concludes that plant growth regulators are absorbed and translocated in the same manner as other organic compounds. Both direct and indirect evidence indicating the translocation of the intact molecule of phenoxy compounds has been presented by Crafts (7), Fang, et al. (9), Hay and Thimann (12), and many others. On the basis of their findings, it was assumed in the