Figure 8.

Proposed model regulating Arabidopsis somatic embryogenesis. Glb1 is a more effective NO scavenger of Glb2, therefore, their suppression would result in a differential accumulation of NO. The Glb1 RNAi line accumulates more NO than the Glb2−/− line. Accumulation of NO activates the transcription of the two ethylene biosynthetic genes (ACC synthase and ACC oxidase) and would possibly increase ethylene level. Ethylene transcriptionally down-regulates many IAA biosynthetic genes and reduces the IAA signal on the zygotic explants. Since IAA is the inductive signal for somatic embryogenesis, a depletion in IAA reduces the ability of the Glb1 RNAi line to produce embryos.