title: Microtubules and CESA tracks at the inner epidermal wall align independently of those on the outer wall of light-grown Arabidopsis hypocotyls.
abstract: Microtubules are classically described as being transverse, which is perpendicular to the direction of cell elongation. However, fixation studies have indicated that microtubules can be variably aligned across the epidermis of elongating shoots. In addition, microtubules are reported to have different orientations on inner and outer epidermal surfaces, undermining the idea of hoop-reinforcement. Here, long-term movies of Arabidopsis seedlings expressing GFP-TUA6 allowed microtubule alignment to be directly correlated with the rate of elongation within individual growing cells. We also investigated whether microtubule alignment at the inner or the outer epidermal wall better reflected the growth rate. Movies confirmed that transverse microtubules form on the inner wall throughout elongation, but orientation of microtubules is variable at the outer wall, where they tend to become transverse only during episodes of accelerated growth. Because this appears to contradict the concept that circumferential arrays of transverse microtubules or microfibrils are essential for cell elongation, we checked the organisation of cellulose synthase tracks using GFP-CESA3 and found a similar mismatch between trajectories on inner and outer epidermal surfaces. We conclude that microtubule alignment on the inner wall appears to be a more stable predictor of growth anisotropy, whereas outer-wall alignment is more sensitive to the elongation rate.
authors.affiliation: Department of Cell and Developmental Biology, John Innes Centre, Colney, Norwich NR4 7UH, UK. jordi.chan@bbsrc.ac.uk
authors.forename: Jordi
authors.initials: J
authors.lastname: Chan
authors.forename: Magdalena
authors.initials: M
authors.lastname: Eder
authors.forename: Elizabeth Faris
authors.initials: EF
authors.lastname: Crowell
authors.forename: Janet
authors.initials: J
authors.lastname: Hampson
authors.forename: Grant
authors.initials: G
authors.lastname: Calder
authors.forename: Clive
authors.initials: C
authors.lastname: Lloyd
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D008870:Microtubules / Q000235:genetics / Q000378:metabolism*; D019441:Plant Epidermis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D021381:Protein Transport
chemical_list: D029681:Arabidopsis Proteins; C516179:At5g05170 protein, Arabidopsis; D005964:Glucosyltransferases