Asymmetric responses of the woody poplar taproot axis to bending stress

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Mechanical bending stress can result in cell wall strengthening and increased wood formation across root axes together with an attendant asymmetrical accumulation of phytohormones. De Zio et al. show how different mechanical force intensities act across the compressed concave and stretched convex sides of the woody bent poplar taproot.

Model summarizing the main anatomical, phytohormonal and proteomical changes observed in the convex and concave sides of three bent taproot sectors
Model summarizing the main anatomical, phytohormonal and proteomical changes observed in the convex and concave sides of three bent taproot sectors (ABS, BS and BBS). Phytohormone (IAA, ABA, GAs, Kin and ethylene) changes are represented by diverse coloured blocks. Proteomic and anatomical changes are indicated by arrows. Zones with the highest lateral root number and lignin content are also reported. ABS, above bending sector; AlaT1, alanine aminotransferase 1 (spot 20); Ara4, ara4-interacting protein (spot 1); BS, bending sector; BBS, below bending sector; CBS1, cystathionine-β-synthase 1 (spot 60); CCN, cambial cell number; CDC48, cell division cycle protein 48 (spot 2); ERP, ethylene-responsive protein; MMSDH, methylmalonate semialdehyde dehydrogenase (spot 17); NDPK, nucleoside diphosphate kinase (spot 64); RPT, relative phloem thickness; RXT, relative xylem thickness; SHMT, serine hydroxymethyltransferase (spot 19); SVA, specific vessel area; SVN; specific vessel number.

The results show that, in contrast to the response of the poplar stem, bending stress applied to woody poplar taproots results in increased wood formation toward the concave side (compressed zone), characterized by the highest values of quantity of cambial cells, xylem thickness and lignin content. The highest quantity of lateral roots is revealed in the stretched zone of the convex side, which constitutes the site for an asymmetrical accumulation of auxin, the phytohormone responsible for triggering lignin deposition and cell wall strengthening in the concave sides.

Root Biology Issue This paper is part of the Root Biology Special Issue.

Reference

Elena De Zio, Dalila Trupiano, Antonio Montagnoli, Mattia Terzaghi, Donato Chiatante, Alessandro Grosso, Mauro Marra, Andrea Scaloni, Gabriella S. Scippa, 2016, 'Poplar woody taproot under bending stress: the asymmetric response of the convex and concave sides', Annals of Botany, vol. 118, no. 4, pp. 865-883 http://dx.doi.org/10.1093/aob/mcw159


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