Metabolic Study on C∧29-Brassinosteroids in Young Rice Plants

It has been recently demonstrated the presence of not only biosysnthesis, but also and biosynthesis in plants, suggesting that BRs biosynthesis are complicatedly connected to produce biologically active BR (s). This prompted us to investigation of metabolism of a , 28-homoCS in seedlings of rice from which such as 28-homoTE and 28-homoTY have been identified. In vitro enzyme conversion study using a crude enzyme solution prepared from rice seedlings revealed that 28-homoCS is converted into both CS and 26-nor-28-homoCS, but their reversed reaction did not occur. This indicated that 28-homoCS is biosynthetically converted into more biologically active , CS by C-28 demethylation and biodegraded into 26-nor-28-homoCS by C-26 demethylation. Next, bio-conversion of 28-homoCS to 28-homoBL was examined by the same enzyme solution. No 28-homoBL as a metabolite of 28-homoCS was detected, meaning that biosynthetic reaction for 28-homoCS to 28-homoBL is not contained, and main connection of and biosynthesis is between CS and 28-homoCS in the rice seedling. This study is the first demonstrated that and bionsynthetic pathways are connected, and that biosynthetic pathway is an alternative biosynthetic pathway to produce more biologically active , CS in plant.