Auxin acts upstream of ethylene biosynthesis. A, Average hypocotyl length of 7-d-old Arabidopsis seedlings Col-0 (gray) and ein2-1 (blue) with and without NAA. Control represents untreated seedlings developed under +DIF (n = 5 × 25). B, Total ethylene emitted per hour of Arabidopsis seedlings grown under −DIF with and without 1 µm
NAA (n = 6 × 30) measured at midday (6 h). C and D, The effect of 10 µm ACC and 1 µm
NAA application on hypocotyl elongation in acs2,4,5,6,7,8,9,11 (acs2-1acs4-1acs5-2acs6-1acs7-1acs9-1amiRacs8acs11; purple) seedlings grown for 7 d under −DIF and wild-type seedlings grown in the presence of AVG (gray; n = 5 × 25). Bars represent means ± se. Bars with different letters differ significantly (P < 0.05). E, ACS (2,4,5,6,7,8,9,11)::GUS staining in 7-d-old seedlings in the basal part of the hypocotyl under +DIF, −DIF, and −DIF in the presence of 1 µm
NAA performed at midday (6 h).