Plant and Cell Physiology Advance Access originally published online on December 13, 2006
Plant and Cell Physiology 2007 48(1):159-168; doi:10.1093/pcp/pcl047
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Wall Ingrowths in Epidermal Transfer Cells of Vicia faba Cotyledons are Modified Primary Walls Marked by Localized Accumulations of Arabinogalactan Proteins
1Southern Weed Science Research Unit, USDA-ARS, Stoneville, MS 38776-0350, USA
2 School of Environmental and Life Sciences, The University of Newcastle, Newcastle, NSW 2308, Australia
*Corresponding author: E-mail, David.McCurdy{at}newcastle.edu.au; Fax, +61-2-49-21-6923.
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Abstract |
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Despite the importance of transfer cells in enhancing nutrient transport in plants, little is known about how deposition of the complex morphology of their wall ingrowths is regulated. We probed thin sections of mature cotyledon epidermal transfer cells of Vicia faba with affinity probes and antibodies specific to polysaccharides and glycoproteins, to determine the distribution of these components in their walls. Walls of these transfer cells consist of the pre-existing primary wall, a uniformly deposited wall layer and wall ingrowths which are comprised of two regions; an electron-opaque inner region and an electron-translucent outer region. The primary wall reacted strongly with antibodies against esterified pectin, xyloglucan, the side chains of rhamnogalaturonan-1 and a cellulase–gold affinity probe. The electron-opaque inner region of wall ingrowths displayed a similar labeling pattern to that of the primary wall, showing strong cross-reactivity with all antibodies tested, except those reacting against highly de-esterified pectins. The electron-opaque outer layer of developmentally more mature wall ingrowths reacted strongly with anti-callose monoclonal and polyclonal antibodies, but showed no reaction for pectin or xyloglucan antibodies or the cellulase–gold affinity probe. The plasma membrane–wall interface was labeled strongly with anti-arabinogalactan protein (AGP) antibodies, with some AGP-reactive antibodies also labeling the electron-translucent zone. Nascent wall ingrowths were labeled specifically with AGPs but not anti-callose. A reduction in wall ingrowth density was observed when developing transfer cells were exposed to ß-D-glucosyl Yariv reagent compared with controls. Our results indicate that wall ingrowths of transfer cells are primary wall-like in composition and probably require AGPs for localized deposition.
Keywords: Arabinogalactan proteins - Cell wall - Immunocytochemistry - Transfer cells - Vicia faba - Wall ingrowths
Abbreviations:
AGP, arabinogalactan protein; BSA, bovine seum albumin; 
GalY, -D-galactosyl Yariv reagent; ßGlcY, ß-D-glucosyl Yariv reagent; GPI, glycosylphosphatidylinositol; PBS, phosphate-buffered saline; RG, rhamnogalacturonan; SEM, scanning electron microscopy.
3 Present address: Microscopy Unit, CSIRO Plant Industry, Canberra, ACT, 2601, Australia.
(Received September 13, 2006; Accepted November 25, 2006)
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