Sunflower (Helianthus annuusL.) seedlings were grown in aeroponic chambers which allowed for easy access to and easy harvesting of undamaged roots. In different portions of these roots we followed the rate of ethylene production, levels of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), N‐malonyl‐ACC and ACC oxidase mRNA and activity of ACC oxidase. ACC oxidase was measured with an in vitro assay, ACC and N‐malonyl‐ACC by selected ion monitoring gas chromatography‐mass spectrometry. Ethylene production was highest in the tip of the root and tower in the middle and basal (part nearest the hypocotyl) portions of the root. The levels of ACC and ACC oxidase mRNA mirrored the levels of ethylene production. The lowest quantities of N‐malonyl‐ACC were found in the root tips. Upon gentle transfer of seedlings from an aeroponic system to treatment tubes, ACC content transiently increased; the greatest increase occurred in the tips. This brief rise in ACC content was not correlated with an increase in ethylene production. ACC oxidase activity was lowest in the tip and higher in the middle and base; the opposite of the pattern of ethylene production. Treating the seedlings with ACC produced a rapid rise in ACC content and ethylene production and inhibited root elongation. ACC oxidase activity was not induc