Absorption and Translocation of 2,4-Dichlorophenoxyacetic Acid

Abstract

1. The pronounced morphological response in plants to 2,4- dichlorophenoxyacetic acid is useful in studies of translocation. 2. The regulator passed upward but not downward through dead segments of stems. 3. Stomata did not appear to be important portals for entry of the compound into the leaves when it was used in aqueous sprays. Leaves of young soybeans absorbed maximum amounts of the growth regulator within 6 hours after application. 4. The movement of food materials was regulated by partial clipping of leaves, defoliation, and reduced light intensity. When the growth regulator was applied to aerial portions of plants, the substance readily moved downward whenever translocation of synthesized materials occurred. 5. More extensive growth inhibition of young red kidney bean plants at primary leaf stage resulted when the substance was added to the base of the blade than when added near the tip. When the compound was added to a primary leaf of a young bean plant more extensive growth inhibition resulted when translocation of the growth substance was rapid than when it was slow. 6. When the growth regulator was added to the primary leaf of kidney beans, it was rapidly translocated basipetally to the stem. In one experiment leaves treated with 40 gamma of the growth regulator had to remain on the plant for 24 hours for maximum amount of compound to reach the stem. Experiments in which alfalfa was sprayed with the growth regulator and then clipped at subsequent intervals showed that much of the compound was translocated from upper to lower plant parts within 1 hour. The velocity of downward movement is markedly influenced by the photosynthetic activity of the plant and the age of the tissue involved. 7. When upper portions of stems or of younger leaves were treated with the compound, apical growth was inhibited, much over-all stunting of plants occurred, and axillary shoots often developed. When lower portions of stems or of older leaves were treated much less stunting of plants occurred. There is as yet no explanation for this occurrence. Proximity to the apical meristem, ease of entrance into the leaf, rapidity or readiness of transport of the compound-all may be involved.