title: Xyloglucan endotransglucosylase/hydrolase (XTH) overexpression affects growth and cell wall mechanics in etiolated Arabidopsis hypocotyls.
abstract: Growth and biomechanics of etiolated hypocotyls from Arabidopsis thaliana lines overexpressing xyloglucan endotransglucosylase/hydrolase AtXTH18, AtXTH19, AtXTH20, and PttXET16-34 were studied. Overexpression of AtXTH18, AtXTH19, and AtXTH20 stimulated growth of hypocotyls, while PttXET16-34 overexpression did not show this effect. In vitro extension of frozen/thawed hypocotyls measured by a constant-load extensiometer started from a high-amplitude initial deformation followed by a slow time-dependent creep. Creep of growing XTH-overexpressing (OE) hypocotyls was more linear in time compared with the wild type at pH 5.0, reflecting their higher potential for long-term extension. XTH-OE plants deposited 65-84% more cell wall material per hypocotyl cross-sectional area than wild-type plants. As a result, their wall stress under each external load was lower than in the wild-type. Growing XTH-OE hypocotyls had higher values of initial deformation·stress(-1) compared with the wild type. Plotting creep rates for each line under different loads against the respective wall stress values gave straight lines. Their slopes and intercepts with the abscissa correspond to ϕ (in vitro cell wall extensibility) and y (in vitro cell wall yield threshold) values characterizing cell wall material properties. The wall material in XTH-OE lines was more pliant than in the wild type due to lower y values. In contrast, the acid-induced wall extension in vitro resulted from increasing ϕ values. Thus, three factors contributed to the XTH-OE-stimulated growth in Arabidopsis hypocotyls: their more linear creep, higher values of initial deformation·stress(-1), and lower y values.
authors.affiliation: Department of Biology, Plant Growth and Development, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.
authors.forename: Eva
authors.initials: E
authors.lastname: Miedes
authors.forename: Dmitry
authors.initials: D
authors.lastname: Suslov
authors.forename: Filip
authors.initials: F
authors.lastname: Vandenbussche
authors.forename: Kim
authors.initials: K
authors.lastname: Kenobi
authors.forename: Alexander
authors.initials: A
authors.lastname: Ivakov
authors.forename: Dominique
authors.initials: D
authors.lastname: Van Der Straeten
authors.forename: Ester P
authors.initials: EP
authors.lastname: Lorences
authors.forename: Ewa J
authors.initials: EJ
authors.lastname: Mellerowicz
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Verbelen
authors.forename: Kris
authors.initials: K
authors.lastname: Vissenberg
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology; D002473:Cell Wall / Q000378:metabolism / Q000502:physiology*; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D016695:Glycosyltransferases / Q000096:biosynthesis / Q000502:physiology*; D018546:Hypocotyl / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism / Q000502:physiology; D060888:Real-Time Polymerase Chain Reaction; D013718:Tensile Strength
chemical_list: D016695:Glycosyltransferases; C473049:xyloglucan - xyloglucosyltransferase
keywords: Arabidopsis hypocotyl; XTH; cell wall; creep test; extensiometry; growth