Abstract
Catchweed bedstraw is famous for its ability to adhere to other objects due to the presence of numerous trichomes surrounding the stem and mericarps and on the surfaces of the leaves. These trichomes serve as an efficient vector for the movement of the propagules via animals. In this study, we examined the structure and composition of the mericarp trichomes by microscopic and immunocytochemical techniques to determine the distribution of polysaccharides. Trichomes present around the mericarps are distinguished by a pronounced hooked tip, resembling in many ways those on Velcro™. In semi-thin sections, the hooked area of the trichome contains little or no lumen but rather appears to be solidly composed of cell wall material. This solid hook appears to be divided into a plug-like zone of material and a highly thickened primary wall. These trichomes are also compositionally unique. They contain very little xyloglucan, even though other tissues in the plant reacted strongly with antibodies that recognize these polysaccharides. The distribution of pectin epitopes on these hooked trichomes was extremely distinctive, with each of the antibodies recognizing domains along the surface of the primary wall and/or in the plug area. Despite the heavily thickened nature of the walls of these trichomes, xylans were not present. Thus, the unique plugged, thickened, and hooked tip of these trichomes appears to be the result of a specific combination and distribution of various pectic polysaccharide molecules. This unusual wall composition may facilitate the formation of highly curved structures that might be difficult to form with the more rigid xyloglucans and xylans.
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Abbreviations
- RGI:
-
rhamnogalacturonan I
References
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Acknowledgements
Andrew J. Bowling was supported in part by the USDA-ARS Research Associate program funding. We thank the many visitors to our poster at the Weed Science Society of America meeting, especially A. DiTommaso, for their many comments on this species and the nature of trichomes in this and related species. Dr. Jarrod Leland graciously allowed the use of his stereo microscope and camera for the examination of living specimens. J. Paul Knox generously provided LM15 antibodies for this study. Production of the CCRC monoclonal antibodies was supported by a NSF grant to Michael Hahn, Complex Carbohydrate Center, U Georgia. Mention of a trademark, proprietary product or brand does not constitute an endorsement of that product or brand by the USDA.
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An erratum to this article can be found at http://dx.doi.org/10.1007/s00709-008-0008-5
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Bowling, A.J., Maxwell, H.B. & Vaughn, K.C. Unusual trichome structure and composition in mericarps of catchweed bedstraw (Galium aparine). Protoplasma 233, 223–230 (2008). https://doi.org/10.1007/s00709-008-0006-7
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DOI: https://doi.org/10.1007/s00709-008-0006-7