The Differential Action of 2,4 –Dichlorophenoxyacetic Acid on the Hypocotyl and Radicle of Germinating Seedlings

Abstract

Studies with the germination inhibitors 2,4-dichlorophenoxyacetic acid (2,4-D) and 4 amino-3,5,6-trichloropicolinic acid (Tordon) have shown that seedlings, treated with concentrations of these inhibitors which just permit germination, are considerably shortened in length and frequently terminate in dome-like callus growths. The callus-tissue-distortion seemed confined to the radicle, suggesting that the cells of the radicle might be in some way distinct from those of the hypocotyl. Germinating seeds treated with 2,4-D at concentrations ranging from 0.1 to 1000 parts per million show a decreasing percentage of germination corresponding to the rise in 2,4-D concentration. Observations at set time intervals after imbibition reveal not only that there is a similar correlation in the reduction of overall seedling length, but also that the ratio of hypocotyl length to radicle length is altered by increasing 2,4-D concentrations. Such observations suggest that the cells of the radicle might be physiologically distinct from those of the hypocotyl.