Diagram illustrating light, NO, ethylene (ET), and auxin (AUX) cross talk during the acquisition of photomorphogenic traits in tomato seedlings. During light-evoked cotyledon greening and chloroplast differentiation, negative and positive feedback regulatory loops orchestrate NO-ET and NO-AUX interactions, respectively. The mutual NO-ET antagonism occurs at biosynthetic levels involving the negative regulation of NR and ACO by ET and NO, respectively. By repressing negative regulators of light signal transduction such as DET1, DDB1, and COP1 and modulating the AUX-ET balance, NO promotes the accumulation of the chloroplast differentiation transcription factor GLK and inhibits key plastid division genes such as FTsZs, ARCs, CRL, and Min. Biosynthetic enzymes are represented with gray ovals. Arrows at the ends of lines indicate stimulatory effects, whereas bars indicate inhibitory effects.