Interactions between ethylene and auxins with gibberellins in the control of hypocotyl growth in Arabidopsis

Signalling pathways are currently viewed as an intricate network ultimately linking the internal and external cues with the phenotype of the plant, resulting from the activity of response genes and their products. We have analysed the interactions between ethylene and two other hormones, auxins, and gibberellins (GA). Each one of these growth factors can promote hypocotyl elongation of Arabidopsis seedlings grown in the light on a medium with a relatively low nutrient concentration. Exogenously applied ethylene and GA exert their effects on hypocotyl elongation in a synergistic manner. Auxin and GA have at least an additive effect enhancing hypocotyl elongation. We also compared growth of a GA insensitive mutant (gai) and an ethylene resistant mutant (etrl-3) with wild type Arabidopsis plants. Taken together, the results indicate that hypocotyl elongation is mainly mediated via the GA signalling pathway and that ethylene and auxin enhance the response to GA.