Patterns of Phenoxy Herbicide Translocation in Bean Seedlings

Abstract

The translocation of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and 2,4-D [(2,4-dichlorophenoxy) acetic acid] in bean (Phaseolus vulgarisL. ‘Stringless Greenpod’) seedlings was studied.14C-labeled herbicides in amounts of 0.75 to μg were injected into the center of the stem at the cotyledonary node with a 1-μL syringe pipette. The effects of time and duration of treatment, herbicide concentration, and herbicide interaction on acropetal and basipetal translocation subsequent to treatment were determined. There was considerable basipetal as well as acropetal translocation of herbicide from the site of injection. Acropetal translocation of 2,4,5-T to primary leaves was very rapid until 2 hr after treatment, and during the following hours of treatment the14C disappeared from the primary leaves. Acropetal translocation of 2,4,5-T to the young shoots was slow but continuous up to 6 hr after treatment, did not decrease during the latter hours of treatment, and was enhanced by high 2,4,5-T treatment levels. Translocation of 2,4,5-T to the nutrient solution continued for at least 72 hr after treatment while the roots accumulated maximum amounts in 6 to 12 hr. High treatment levels of 2,4,5-T enhanced the translocation of 2,4-D in the young shoots. However, 2,4-D did not promote the translocation of 2,4,5-T. Considerable variation occurred in the total translocation of 2,4,5-T when treatments were made at various times during the day. Translocation rates to the nutrient solution were at a maximum at about 12 A.M. and 12 P.M. each day regardless of the time of application of the 2,4,5-T.