Effects of Dimethyl Sulfoxide and pH on Indoleacetic Acid-Induced Lateral Root Formation in the Radish Seedling Root

Segments (2.5 cm) cut from 3-day-old seedling roots of radish (Raphanus sativus L. ;Scarlet Globe') were cultured in medium with or without indoleacetic acid (IAA). Lateral root primordia frequency, determined for the central centimeter of segments, was dependent on IAA concentration and on conditions affecting IAA uptake. Dimethyl sulfoxide treatment, or a relatively low medium pH, greatly enhanced the response to exogenous IAA. It was concluded that a permeation barrier exists between the external medium and the hormone responsive sites within the radish seedling root.