title: Cell wall hemicellulose contributes significantly to aluminum adsorption and root growth in Arabidopsis.
abstract: The cell wall (CW) has been recognized as the major target of aluminum (Al) toxicity. However, the components responsible for Al accumulation and the mechanisms of Al-induced CW function disruption are still elusive. The contribution of different CW components (pectin, hemicellulose 1 [HC1], and HC2) to adsorb Al and the effect of Al on xyloglucan endotransglucosylase/hydrolyase activity were investigated in Arabidopsis (Arabidopsis thaliana) in this study. A fractionation procedure was optimized to effectively extract different CW components, especially to prevent the HC fraction from pectin contamination. When CW materials extracted from Al-treated roots (50 μm Al for 24 h) were fractionated, about 75% of CW Al accumulated in the HC1 fraction. A time-dependent kinetic study showed that only when the HC1 fraction was removed was the amount of Al adsorbed decreased sharply. In vivo localization of xyloglucan endotransglucosylase (XET) activity showed that Al greatly inhibited this enzyme activity within 30 min of exposure, which was concomitant with Al-induced callose deposition in roots. Results from real-time reverse transcription-polymerase chain reaction indicated that three genes may constitute the major contributors to XET activity and that the inhibition of XET activity by Al is caused by transcriptional regulation. These results, to our knowledge for the first time, demonstrate that HC is the major pool for Al accumulation. Furthermore, Al-induced reduction in XET activity could play an important role in Al-induced root growth inhibition.
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, China.
authors.forename: Jian Li
authors.initials: JL
authors.lastname: Yang
authors.forename: Xiao Fang
authors.initials: XF
authors.lastname: Zhu
authors.forename: You Xiang
authors.initials: YX
authors.lastname: Peng
authors.forename: Cheng
authors.initials: C
authors.lastname: Zheng
authors.forename: Gui Xin
authors.initials: GX
authors.lastname: Li
authors.forename: Yu
authors.initials: Y
authors.lastname: Liu
authors.forename: Yuan Zhi
authors.initials: YZ
authors.lastname: Shi
authors.forename: Shao Jian
authors.initials: SJ
authors.lastname: Zheng
mesh_terms: D000327:Adsorption; D000535:Aluminum / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000737:chemistry*; D018506:Gene Expression Regulation, Plant; D016695:Glycosyltransferases / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics
chemical_list: D011134:Polysaccharides; D018749:RNA, Plant; C007916:hemicellulose; D000535:Aluminum; D016695:Glycosyltransferases; C473049:xyloglucan - xyloglucosyltransferase