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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Cell Wall Proteome in the Maize Primary Root Elongation Zone. II. Region-Specific Changes in Water Soluble and Lightly Ionically Bound Proteins under Water Deficit^1,[W],[OA]

Division of Plant Sciences (J.Z., M.E.L., I.-J.C., H.T.N., R.E.S.) and Molecular Cytology Core (M.S.), University of Missouri, Columbia, Missouri 65211; Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (S.A., E.L.M., S.C., D.P.S.); and Department of Plants, Soils and Climate, Utah State University, Logan, Utah 84322 (Y.W.)

Previous work on the adaptation of maize (Zea mays) primary roots to water deficit showed that cell elongation is maintained preferentially toward the apex, and that this response involves modification of cell wall extension properties. To gain a comprehensive understanding of how cell wall protein (CWP) composition changes in association with the differential growth responses to water deficit in different regions of the elongation zone, a proteomics approach was used to examine water soluble and loosely ionically bound CWPs. The results revealed major and predominantly region-specific changes in protein profiles between well-watered and water-stressed roots. In total, 152 water deficit-responsive proteins were identified and categorized into five groups based on their potential function in the cell wall: reactive oxygen species (ROS) metabolism, defense and detoxification, hydrolases, carbohydrate metabolism, and other/unknown. The results indicate that stress-induced changes in CWPs involve multiple processes that are likely to regulate the response of cell elongation. In particular, the changes in protein abundance related to ROS metabolism predicted an increase in apoplastic ROS production in the apical region of the elongation zone of water-stressed roots. This was verified by quantification of hydrogen peroxide content in extracted apoplastic fluid and by in situ imaging of apoplastic ROS levels. This response could contribute directly to the enhancement of wall loosening in this region. This large-scale proteomic analysis provides novel insights into the complexity of mechanisms that regulate root growth under water deficit conditions and highlights the spatial differences in CWP composition in the root elongation zone.

² These authors contributed equally to the article.

³ Present address: Department of Botany, University of Florida, Gainesville, FL 32610.

⁴ Present address: Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

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: Robert E. Sharp (sharpr{at}missouri.edu).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.107250

^* Corresponding author; e-mail sharpr{at}missouri.edu.

Received August 11, 2007; accepted October 13, 2007; published October 19, 2007.

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