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First published online December 29, 2005; 10.1104/pp.105.073130 Plant Physiology 140:603-612 (2006) © 2006 American Society of Plant Biologists
Progressive Inhibition by Water Deficit of Cell Wall Extensibility and Growth along the Elongation Zone of Maize Roots Is Related to Increased Lignin Metabolism and Progressive Stelar Accumulation of Wall Phenolics1Plant Physiology Laboratory, Department of Environmental, Water, and Agricultural Engineering, Faculty of Civil and Environmental Engineering (L.F., R.L., P.M.N.) and Faculty of Biology (S.G.), Technion-Israel Institute of Technology, Haifa 32000, Israel; Plant Physiology Laboratory, Department of Information and Biological Sciences, Graduate School of Natural Sciences, Nagoya City University, Nagoya 467–8501, Japan (E.T.); and Biology and Chemistry Laboratory, Tezukayama University, Nara 631–8585, Japan (R.Y.)
Water deficit caused by addition of polyethylene glycol 6000 at –0.5 MPa water potential to well-aerated nutrient solution for 48 h inhibited the elongation of maize (Zea mays) seedling primary roots. Segmental growth rates in the root elongation zone were maintained 0 to 3 mm behind the tip, but in comparison with well-watered control roots, progressive growth inhibition was initiated by water deficit as expanding cells crossed the region 3 to 9 mm behind the tip. The mechanical extensibility of the cell walls was also progressively inhibited. We investigated the possible involvement in root growth inhibition by water deficit of alterations in metabolism and accumulation of wall-linked phenolic substances. Water deficit increased expression in the root elongation zone of transcripts of two genes involved in lignin biosynthesis, cinnamoyl-CoA reductase 1 and 2, after only 1 h, i.e. before decreases in wall extensibility. Further increases in transcript expression and increased lignin staining were detected after 48 h. Progressive stress-induced increases in wall-linked phenolics at 3 to 6 and 6 to 9 mm behind the root tip were detected by comparing Fourier transform infrared spectra and UV-fluorescence images of isolated cell walls from water deficit and control roots. Increased UV fluorescence and lignin staining colocated to vascular tissues in the stele. Longitudinal bisection of the elongation zone resulted in inward curvature, suggesting that inner, stelar tissues were also rate limiting for root growth. We suggest that spatially localized changes in wall-phenolic metabolism are involved in the progressive inhibition of wall extensibility and root growth and may facilitate root acclimation to drying environments.
1 This work was supported by FMW chair and Manlam (grant to P.M.N.) and a Zeff Fellowship (to R.L.). The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Peter M. Neumann (agpetern{at}tx.technion.ac.il). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.073130. * Corresponding author; e-mail agpetern{at}tx.technion.ac.il; fax 972–4–8228898. Received October 20, 2005; returned for revision October 20, 2005; accepted November 21, 2005. This article has been cited by other articles:
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