Response of maize seedling roots to changing ethylene concentrations

Maize roots (Zea mays, cv. DK 626) growing in aerated solutions showed striking variations in the amount of ethylene produced during different stages of development. As endogenous ethylene increases, root elongation decreases. Exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) supplied to these roots also inhibited their elongation and increased both the fresh weight of the apex and the ethylene produced. The inhibitor of ethylene biosynthesis, 2-aminoethoxyvinyl glycine (AVG), and the inhibitor of ethylene action, silver thiosulfate (STS), also reduced growth and increased swelling. As growth diminishes at reduced ethylene concentrations or with impeded ethylene action, these results support the view that ethylene is necessary for root growth. As ACC treatment also inhibited root elongation, it appears that ethylene was inhibitory at both low and high concentrations. Whereas ACC stimulated ethylene production 4 h after the beginning of treatment, inhibition of root elongation and promotion of fresh weight advanced slowly and needed 24 h to be established. At that time, root elongation reached a maximum response of 60% inhibition and 50% increase in weight. At 48 h, higher doses of ACC were required to provoke the same response as at 24 h. This suggests that the root growth progressively accomodates to higher ethylene concentrations.