title: Biosynthetic relationship between C₂₈-brassinosteroids and C₂₉-brassinosteroids in rice (Oryza sativa) seedlings.
abstract: A crude enzyme solution was prepared from young rice seedlings, and the metabolism of C29-brassinosteroids identified from the seedlings was examined. When 28-homoteasterone was added as a substrate, 28-homotyphasterol, teasterone, and 26-nor-28-homoteasterone were characterized as enzyme products by GC-MS/SIM analysis. With 28-homotyphasterol, 28-homoteasterone, typhasterol, 28-homocastasterone, and 26-nor-28-homotyphasterol were formed and identified as products. When 28-homocastasterone was used, castasterone and 26-nor-28-homocastasterone were identified as products. Together with the reduced biological activity of C29-brassinosteroids and their metabolites in the rice lamina inclination assay, these metabolic studies suggest a biosynthetic sequence, 28-homoteasterone↔28-homotyphasterol→28-homocastasterone for C29-brassinosteroid biosynthesis is connected to the biosynthetic sequence teasterone↔typhasterol→castasterone for C28-brassinosteroids by C-28 demethylation, i.e., in order to increase biological activity in the rice plant. Additionally, the C29-brassinosteroids seem to bio-degrade their C-26 demethylated C28-brassinosteroid analogs to reduce brassinosteroid activity in planta. In conclusion, the biosynthesis of C29-brassinosteroids is a likely alternative route to the biologically-active brassinosteroid, castasterone, in rice.
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Se-Hwan
authors.initials: SH
authors.lastname: Joo
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Mun-Seok
authors.initials: MS
authors.lastname: Jang
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Min Kyun
authors.initials: MK
authors.lastname: Kim
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, Republic of Korea.
authors.forename: Ji-Eun
authors.initials: JE
authors.lastname: Lee
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, Republic of Korea. Electronic address: skkimbio@cau.ac.kr.
authors.forename: Seong-Ki
authors.initials: SK
authors.lastname: Kim
mesh_terms: D060406:Brassinosteroids / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D002777:Cholestanols / Q000737:chemistry / Q000378:metabolism; D002778:Cholestanones / Q000737:chemistry / Q000378:metabolism; D015394:Molecular Structure; D012275:Oryza / Q000737:chemistry*; D036226:Seedlings / Q000737:chemistry*
chemical_list: D060406:Brassinosteroids; D002777:Cholestanols; D002778:Cholestanones; C083545:castasterone; C070164:homocastasterone
keywords: Biosynthesis; C(29)-brassinosteroids; C-28 demethylation; Castasterone; Gramineae; Oryza sativa; Rice