Brassinolide and [26, 28-2H6]Brassinolide are differently demethylated by loss of c-26 and c-28, respectively, in Marchantia polymorpha

Metabolism of brassinolide in Marchantia polymorpha was investigated by use of in vivo suspension cultured cells. GC-MS analysis of metabolites derived from non-labelled brassinolide and [26, 28-H-2(6)]brassinolide revealed that brassinolide was converted to 26-norbrassinolide while [26, 28-H-2(6)]brassinolide to [26-H-2(3)]28-norbrassinolide. It seems that Marchantia cells recognized [26, 28-H-2(6)]brassinolide as a xenobiotic rather than brassinolide and deteriums attached to C-28 significantly affect demethylation reaction due to isotopic effect. Thus, demethylation of brassinolide in planta seems to proceed by loss of C-26 rather than C-28, The present finding is the first evidence for demethylation metabolism of brassinosteroids. The biological activity of 26-norbrassinolide was 10-fold reduced as shown by the rice lamina inclination test. However, because of its high biological activity, it remains difficult to conclude whether or not C-26 demethylation serves as an important deactivation process of brassinolide.