title: Poplar woody taproot under bending stress: the asymmetric response of the convex and concave sides.
abstract: Background and Aims Progress has been made in understanding the physiological and molecular basis of root response to mechanical stress, especially in the model plant Arabidopsis thaliana, in which bending causes the initiation of lateral root primordia toward the convex side of the bent root. In the case of woody roots, it has been reported that mechanical stress induces an asymmetric distribution of lateral roots and reaction wood formation, but the mechanisms underlying these responses are largely unknown. In the present work, the hypothesis was tested that bending could determine an asymmetric response in the two sides of the main root axis as cells are stretched on the convex side and compressed on the concave side. Methods Woody taproots of 20 seedlings were bent to an angle of 90° using a steel net. Changes in the anatomy, lignin and phytohormone content and proteome expression in the two sides of the bent root were analysed; anatomical changes, including dissimilarities and similarities to those found in poplar bent woody stem, were also considered. Key Results Compression forces at the concave side of poplar root induced the formation of reaction wood which presented a high lignin content and was associated with the induction of cambium cell activity. Auxin seemed to be the main hormone triggering lignin deposition and cell wall strengthening in the concave sides. Abscisic acid appeared to function in the water stress response induced by xylem structures and/or osmotic alterations in the compression sides, whereas gibberellins may control cell elongation and gravitropisms. Conclusions Poplar root reaction wood showed characteristics different from those produced in bent stem. Besides providing biomechanical functions, a bent root ensures water uptake and transport in the deforming condition induced by tension and compression forces by two different strategies: an increase in xylem thickness in the compressed side, and lateral root formation in the tension side.
authors: Dipartimento di Bioscienze e Territorio, University of Molise, 86090 Pesche (IS), Italy.
authors: Elena
authors: E
authors: De Zio
authors: Dipartimento di Bioscienze e Territorio, University of Molise, 86090 Pesche (IS), Italy.
authors: Dalila
authors: D
authors: Trupiano
authors: Dipartimento di Biotecnologie e Scienze della Vita, University of Insubria, 21100 Varese, Italy.
authors: Antonio
authors: A
authors: Montagnoli
authors: Dipartimento di Biotecnologie e Scienze della Vita, University of Insubria, 21100 Varese, Italy.
authors: Mattia
authors: M
authors: Terzaghi
authors: Dipartimento di Biotecnologie e Scienze della Vita, University of Insubria, 21100 Varese, Italy.
authors: Donato
authors: D
authors: Chiatante
authors: Dipartimento di Biologia, University of Rome 'Tor Vergata', 00133 Rome, Italy.
authors: Alessandro
authors: A
authors: Grosso
authors: Dipartimento di Biologia, University of Rome 'Tor Vergata', 00133 Rome, Italy.
authors: Mauro
authors: M
authors: Marra
authors: Proteomics and Mass Spectrometry Laboratory, ISPAAM, National Research Council, 80147 Napoli, Italy.
authors: Andrea
authors: A
authors: Scaloni
authors: Dipartimento di Bioscienze e Territorio, University of Molise, 86090 Pesche (IS), Italy.
authors: Gabriella S
authors: GS
authors: Scippa
keywords: Mechanical stress; phytohormones; proteomics; reaction wood; root anatomy