A Chemical Inhibitor of Auxin-Induced Lateral Root Initiation in Roots of Pisum.

Using a new lateral root initiation assay based on the stimulation or inhibition of indoleacetic acid-induced root initiation in excised root segments of Pisum sativum cultured in vitro, a study has been made of ether-and alcohol soluble inhibitors extracted from seedling roots of Pisum and separated by paper chromatography. Substances with characteristic R_f values in a given solvent system were eluted directly from paper sections into a sterile nutrient medium in which root segments were allowed to develop new root primordia under the influence of added auxin. The detection of an inhibitor was dependent on the degree of suppression of root initiation. Inhibitors of lateral root initiation were detected in both the alkaline and the acidic ether-soluble fraction of a cold absolute ethanol extract of seedling pea roots. A detailed study of the alkaline fraction separated by paper chromatography showed that two inhibitor spots were present. The first compound with R_f0.2-0.3 in an n-butanol-ammonia-water solvent showed a bright-blue fluorescence in ultraviolet light, an orange-red color after spraying with Salkowski reagent and a yellow color with Ehrlich's reagent. The compound was not further characterized. A second compound in the alkaline extract, which appeared to be the most active inhibitor, had an R_f of 0.7-0.8 in the same solvent system, showed no UV-fluorescence. formed a purple-brown color with Salkowski reagent but no color with Ehrlich's reagent. When chromatographed at 23°C, with water-saturated ethyl acetate as the solvent, the compound was apparent as an oily spot at R_f 0.3-0.6. From solubilities, its slightly acidic nature, its reducing properties, its reaction to a variety of color tests, and its ultraviolet absorption characteristics, the inhibitor has been tentatively identified as a phenolic compound. Its possible physiological role in controlling the site of lateral root initiation in pea seedlings has been suggested, but elucidation of its role awaits further physiological study. [ABSTRACT FROM AUTHOR]