The Absorption and Translocation Of 2,4-Dichlorophenoxyacetic Acid by Bean Plants

Abstract

The curvature reaction of kidney bean seedlings was used as a measure of the translocation of 2,4-D from the leaves. When a small quantity of 2,4-D was applied to 1 leaf of a bean seedling under greenhouse conditions, curvature started in approx. 2 hrs., and reached a max. in about 6 hrs., at which time recovery began. The time from appln. of 2,4-D to the beginning of curvature was independent of the amt. of 2,4-D applied. The max. curvature attained was a measure of the amt. of 2,4-D absorbed and translocated, and the rate of bending, once it began, was likewise detd. by the dose. It was found that the 2,4-D moved through the cuticle, epidermis, and mesophyll to the phloem with a velocity of approx. 30[mu]/hr. Once inside the phloem it was translocated several centimeters to the epicotyl at a velocity varying through a range of 10 to 100 cm./hr. After the 2,4-D reached the epicotyl, about 40 min. elapsed before curvature began, and when the supply of 2,4-D to the epicotyl was interrupted, 1 hour elapsed before recovery began. Under the conditions of these tests, the max. amt. of 2,4-D was absorbed by leaves in the first 4.5 hrs. after treatment.