Abstract:To explore the possible mechanism of high rates of ammonium nitrate (NH4NO3) in the regulation of root hair formation, we grew wild type (WT), auxininsensitive and ethyleneinsensitive mutant seedlings on vertically oriented agar plates. Our study found that: (1) high rates of ammonium nitrate (NH4NO3) supply stimulated the branched root hair formation and inhibited root hair elongation. (2) The effect of NH4NO3 on root hair formation were blocked by reactive oxygen species (ROS) and diphenylene iodonium chloride (DPI), suggesting that ROS was involved in NH4NO3induced branched root hair formation. (3) The treatment of auxin or ethylene under high NH4NO3 condition completely inhibited high NH4NO3 induced branched root hair formation. (4) Either eir13 seedlings treated with auxin or aux17 and axr13 treated with ACC, the NH4NO3 induced branched root hair formation was inhibited. The results above showed that ROS, auxin and ethylene involved in high NH4NO3induced branched root hair formation. Auxin played a compensating role in the absence of an ethylene response and ethylene played a supplemental role in the absence of an auxin response. A higher level of auxin was required for preventing branched root hair formation in the absence of ethylene signaling.