An ethylene and ROS-dependent pathway is involved in low ammonium-induced root hair elongation in Arabidopsis seedlings.

Abstract Root hairs are plastic in response to nutrient supply, but relatively little is known about their development under low ammonium (NH 4 + ) conditions. This study showed that reducing NH 4 + for 3 days in wild-type Arabidopsis seedlings resulted in drastic elongation of root hairs. To investigate the possible mediation of ethylene and auxin in this process, seedlings were treated with 2,3,5-triiodobenzoic acid (TIBA, auxin transport inhibitor), 1-naphthylphthalamic acid (NPA, auxin transport inhibitor), p-chlorophenoxy isobutyric acid (PCIB, auxin action inhibitor), aminoethoxyvinylglycine (AVG, chemical inhibitor of ethylene biosynthesis), or silver ions (Ag + , ethylene perception antagonist) under low NH 4 + conditions. Our results showed that TIBA, NPA and PCIB did not inhibit root hair elongation under low NH 4 + conditions, while AVG and Ag + completely inhibited low NH 4 + -induced root hair elongation. This suggested that low NH 4 + -induced root hair elongation was dependent on the ethylene pathway, but not the auxin pathway. Further genetic studies revealed that root hair elongation in auxin-insensitive mutants was sensitive to low NH 4 + treatment, but elongation was less sensitive in ethylene-insensitive mutants than wild-type plants. In addition, low NH 4 + -induced root hair elongation was accompanied by reactive oxygen species (ROS) accumulation. Diphenylene iodonium (DPI, NADPH oxidase inhibitor) and dimethylthiourea (DMTU, ROS scavenger) inhibited low NH 4 + -induced root hair elongation, suggesting that ROS were involved in this process. Moreover, ethylene acted together with ROS to modulate root hair elongation under low NH 4 + conditions. These results demonstrate that a signaling pathway involving ethylene and ROS participates in regulation of root hair elongation when Arabidopsis seedlings are subjected to low NH 4 + conditions.