GC-MS analysis revealed that primary roots of maize contain 6-deoxocathasterone, 6-deoxoteasterone and 6-deoxotyphasterol. These brassinosteroids, and the previously identified campesterol, campestanol, 6-deoxocastasterone and castasterone, in the roots are members of a biosynthetic pathway to castasterone, namely the late C-6 oxidation pathway, suggesting that its biosynthetic pathway is operative in the roots. To verify this, a cell-free enzyme extract was prepared from maize roots, and enzymatic conversions from campesterol to castasterone through the aforementioned sterols and brassinosteroids were examined. The presence for the biosynthetic sequences, campesterol → 24-methylcholest-4-en-3β-ol → 24-methylcholest-4- en-3-one → 24-methylcholest-5 α-cholestan-3-one → campestanol and 6-deoxoteasterone → 6-deoxo-3-dehydroteasterone → 6-deoxotyphasterol → 6-deoxocastasterone → castasterone were demonstrated. These results indicate that maize roots contain a complete set of enzymes involved in the late C-6 oxidation pathway, thereby demonstrating that endogenous brassinosteroids are biosynthesized in the roots.
- Maize root
- The late C-6 oxidation pathway
- Zea mays L.