title: Exogenously applied 24-epi brassinolide reduces lignification and alters cell wall carbohydrate biosynthesis in the secondary xylem of Liriodendron tulipifera.
abstract: The roles of brassinosteroids (BRs) in vasculature development have been implicated based on an analysis of Arabidopsis BR mutants and suspension cells of Zinnia elegans. However, the effects of BRs in vascular development of a woody species have not been demonstrated. In this study, 24-epi brassinolide (BL) was applied to the vascular cambium of a vertical stem of a 2-year-old Liriodendron, and the resulting chemical and anatomical phenotypes were characterized to uncover the roles of BRs in secondary xylem formation of a woody species. The growth in xylary cells was clearly promoted when treated with BL. Statistical analysis indicated that the length of both types of xylary cells (fiber and vessel elements) increased significantly after BL application. Histochemical analysis demonstrated that BL-induced growth promotion involved the acceleration of cell division and cell elongation. Histochemical and expression analysis of several lignin biosynthetic genes indicated that most genes in the phenylpropanoid pathway were significantly down-regulated in BL-treated stems compared to that in control stems. Chemical analysis of secondary xylem demonstrated that BL treatment induced significant modification in the cell wall carbohydrates, including biosynthesis of hemicellulose and cellulose. Lignocellulose crystallinity decreased significantly, and the hemicellulose composition changed with significant increases in galactan and arabinan. Thus, BL has regulatory roles in the biosynthesis and modification of secondary cell wall components and cell wall assembly during secondary xylem development in woody plants.
authors.affiliation: Department of Biosystems Engineering, Korea University, Seoul 136-701, Republic of Korea.
authors.forename: Hyunjung
authors.initials: H
authors.lastname: Jin
authors.affiliation: Department of Biotechnology, Korea University, Seoul 136-701, Republic of Korea.
authors.forename: Jihye
authors.initials: J
authors.lastname: Do
authors.affiliation: Department of Wood and Paper Science, Chungbuk National University, Cheongju 361-763, Republic of Korea.
authors.forename: Soo-Jeong
authors.initials: SJ
authors.lastname: Shin
authors.affiliation: Department of Forest Sciences, Seoul National University, Seoul 151-742, Republic of Korea.
authors.forename: Joon Weon
authors.initials: JW
authors.lastname: Choi
authors.affiliation: Division of Forest Biotechnology, Korea Forest Research Institute, Suwon 441-350, Republic of Korea.
authors.forename: Young Im
authors.initials: YI
authors.lastname: Choi
authors.affiliation: Department of Biotechnology, Korea University, Seoul 136-701, Republic of Korea.
authors.forename: Wook
authors.initials: W
authors.lastname: Kim
authors.affiliation: Department of Biotechnology, Korea University, Seoul 136-701, Republic of Korea. Electronic address: mikwon@korea.ac.kr.
authors.forename: Mi
authors.initials: M
authors.lastname: Kwon
mesh_terms: D060406:Brassinosteroids / Q000737:chemistry / Q000494:pharmacology*; D002241:Carbohydrates / Q000096:biosynthesis*; D002473:Cell Wall / Q000187:drug effects* / Q000378:metabolism; D008031:Lignin / Q000378:metabolism*; D031567:Liriodendron / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D015394:Molecular Structure; D010937:Plant Growth Regulators / Q000737:chemistry / Q000494:pharmacology*; D018547:Plant Stems / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D013260:Steroids, Heterocyclic / Q000737:chemistry / Q000494:pharmacology*; D052584:Xylem / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism
chemical_list: D060406:Brassinosteroids; D002241:Carbohydrates; D010937:Plant Growth Regulators; D013260:Steroids, Heterocyclic; D008031:Lignin; C023623:brassinolide
keywords: Arabinan; Brassinolide (BL); Cell wall; Cellulose; Crystallinity; Galactan; Hemicellulose; Lignin; Liriodendron tulipifera; Magnoliaceae; Pectin; Secondary xylem; Yellow poplar