1,2 ) This process is called de-etiolation or photomorphogenesis. 2,3 ) When plants are grown under light conditions, seedlings show light-adapted development characterized by a decrease of hypocotyl elongation, opened cotyledons, induction of true leaf expansion and biosynthesis of chlorophyll and anthocyanin. 1 ) In dicotyledonous plants, etiolated seedlings grown in the dark have elongated hypocotyls, closed apical hooks, unopened cotyledons, and undeveloped chloroplasts. Light induces transitions from dark-grown (etiolated) to light-grown (de-etiolated) morphology. The results strongly suggest that SL and KAR induce photomorphogenesis of Arabidopsis in an STH7-dependent manner. GR24 and KAR 1 treatment significantly increased the expression level of photosynthesis-related genes LHCB1 and rbcS. Furthermore, the chlorophyll and anthocyanin content was increased in STH7ox lines when de-etiolated with light and GR24-treated plants had enhanced anthocyanin production. Hypocotyl elongation of STH7- SRDX mutants was less sensitive to both GR24 and KAR 1 treatment than that of wild-type Arabidopsis under weak light conditions. In this study, we used STH7-overexpressing ( STH7ox) lines and functionally defective STH7 ( STH7- SRDX) mutants to investigate roles of SLs and KARs in photomorphogenesis of Arabidopsis. GR24 and KAR 1 up-regulate the expression of STH7, encoding a transcription factor belonging to the double B-box zinc finger subfamily. GR24, a synthetic SL and KAR 1, a KAR, inhibit the hypocotyl elongation of Arabidopsis thaliana in a weak light.

Strigolactones (SLs) and karrikins (KARs) regulate photomorphogenesis.

Srdx light or dark