Abstract
Woody plants develop a specialized secondary xylem known as reaction wood to enable formation of an ideal shape. Reaction wood in coniferous species is known as compression wood, and that of woody angiosperms as tension wood. However, the genus Buxus which is classified as an angiosperm, forms compression-wood-like reaction wood. We investigated the mechanism of lignification in coniferous compression wood and Buxus reaction wood: 1) Several lignin synthesis genes were upregulated in differentiating reaction wood of Buxus microphylla; 2) B. microphylla possesses a specific laccase gene that is expressed specifically in differentiating reaction wood (BmLac4); 3) laccase activity localization was closely related to lignification of reaction wood, and laccase activity was high in the secondary wall middle layer; 4) in reaction wood cell walls, galactan was present in the outer portion of the secondary wall middle layer, and the level of xylan was reduced. These findings suggest that lignification in B. microphylla reaction wood is identical to that of coniferous compression wood. These may represent general mechanisms of increasing lignin content in various reaction woods.
Highlights
Woody plants develop a specialized secondary xylem known as reaction wood to enable formation of an ideal shape [1] [2]
We investigated whether the lignification mechanism of Buxus reaction wood is identical to that of compression wood by assessing the lignification process in both Buxusreaction wood and coniferous compression wood
We demonstrated that: 1) expression of a laccase (CoLac1) in Chamaecyparis obtusa is very low in differentiating normal wood but very high in differentiating compression wood; 2) laccase activity is higher in the S2L region than in other parts of the S2 layer; 3) Colac1 is expressed at the onset of secondary wall thickening and is localized to the S2L region [16] [17]
Summary
Woody plants develop a specialized secondary xylem known as reaction wood to enable formation of an ideal shape [1] [2]. Woody gymnosperms (conifers) develop reaction wood on the lower side of inclined stems and branches, which is known as compression wood [3] [4]. Buxus species form no tension wood, and instead develop compression-wood-like reaction wood on the lower side of inclined stems and branches [7], which generates compressive growth stress [8]. Buxus reaction wood is similar in chemical and anatomical features to compression wood [7] [8]; it shows eccentric growth on the lower side of inclined stems and branches; the xylem is darker brown than normal wood; the wood fiber and vessels in the transverse plane are circular; and the wood fiber has a large microfibril angle in the secondary wall, and an increased lignin content in the cell wall. The cell wall develops a highly lignified region in the outer portion of the secondary wall middle layer (S2) [9], which is a remarkable characteristic of coniferous compression wood and known as S2L
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
