Ammonium-Stimulated Root Hair Branching is Enhanced by Methyl Jasmonate and Suppressed by Ethylene in Arabidopsis thaliana

Root hair development is orchestrated by nutritional factors and plant hormones. We investigated the action of ammonium (NH₄+) and its interactions with methyl jasmonate (MeJA) and ethylene in Arabidopsis root hair growth. The formation of root hair branches was dramatically stimulated in media containing 1.25 to 20 mM NH₄+ at pH values of 4.0 to 6.5. The NH₄+-treated root hairs showed a very short tip growth stage and swells on the sides that indicated the emergence of branches. MeJA (0.08 to 10 μM) worked in synergism with NH₄+ to enhance hair branching. In contrast, ethylene had an antagonistic effect; the stimulation of hair branching by NH₄+ was suppressed by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and was diminished in ethylene-overproducing mutant eto1-1 seedlings. Moreover, the application of Ag+, an ethylene inhibitor, reduced the ACC-induced inhibition of NH₄+-stimulated hair branching and restored NH₄+-stimulated hair branching in eto1-1 seedlings. Thus, the actions of jasmonate and ethylene appear to be dependent on nutritional conditions such as available nitrogen.