A Study of the Interaction between Auxin and Ethylene in Wild Type and Transgenic Ethylene‐Insensitive Tobacco during Adventitious Root Formation Induced by Stagnant Root Zone Conditions

Wild type (Wt) and transgenic plants ( etr1‐1 gene from Arabidopsis thaliana; encoding for a defective ethylene receptor; Tetr) of Nicotiana tabacum L. were subjected to experiments to resolve the role of the interaction between ethylene and auxin in waterlogging‐induced adventitious root formation. Plants were grown in aerated or stagnant deoxygenated nutrient solution and treated with the following plant growth regulators: ethylene, the synthetic auxins 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 1‐naphthaleneacetic acid (1‐NAA), and the auxin efflux inhibitor naphthylphthalamic acid (NPA). The superior growth of Wt in stagnant solution suggests that the ability to sense and respond to ethylene partially mediates tolerance to stagnant root zone conditions. Wt produced around 2 ‐ 2.5‐fold more adventitious roots than Tetr in aerated and stagnant solution. Treatment with NPA phenocopied the effects of ethylene insensitivity by reducing the number of adventitious roots on Wt to Tetr levels. Additionally, application of 1‐NAA to the shoot of Tetr increased the number of adventitious roots on Tetr to similar levels as the untreated Wt. However, this level was only around half the number achieved by 1‐NAA‐treated Wt. The results suggest an interplay between ethylene and auxin in the process of adventitious root formation in waterlogged tobacco, most likely on the level of polar auxin transport. However, a separate non‐auxin‐related role as a transcription regulator for genes essential to adventitious root formation cannot be excluded.