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Title: Unusual trichome structure and composition in mericarps of catchweed bedstraw (Calium aparine)

item Bowling, Andrew
item Maxwell, Brian
item Vaughn, Kevin

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2008
Publication Date: 6/26/2008
Citation: Bowling, A.J., Maxwell, B.H., Vaughn, K.C. 2008. Unusual trichome structure and composition in mericarps of catchweed bedstraw (Calium aparine). Protoplasma 233:223-230.

Interpretive Summary: Bedstraw is an unusual weed in that it is able to climb over other plants, much as do vines, but without the twining or tendrils characteristic of vines. We used anatomical and immunochemical techniques to determine why bedstraw has this unique ability. Interestingly bedstraw has trichomes (plant hairs) that are similar to the hook shaped structures on Velcro ™ and a second type of trichome along the ridges of the stem. Immunochemical evidence indicates that the second trichome type has in addition a composition enriched in sticky pectins. The stems are hollow, making the bedstraw plants very light. Thus, both the ability to adhere to other objects through the unique trichomes and the light stem enables bedstraw to scramble through other plants, much as do vines, without the benefit of tendrils or twining stems.

Technical Abstract: Although catchweed bedstraw neither twines or produces tendrils, it has the ability to climb over other vegetation and scramble, much as do vines. In this study, we used microscopic and immunochemical approaches to investigate this apparent ability. Bedstraw stems, leaves and carpels surrounding the flowering structures and seeds are covered with highly barbed or hooked trichomes. Structurally those on leaves and around the fruits resemble the hooks found on Velcro ™ hooks. The trichomes on the stems are concentrated on the four exposed ridges on the stem. Internally the stem consists of a central hollow pith surrounded by an extensive cylinder of lignified xylary fibers. Photosynthetic parenchyma exists as a thin ridge around the periphery, except for the tips of the ridges, where collenchyma cells are present. Immunocytochemical probes indicate that the fibers are highly enriched in sticky de-esterified pectins and that the collenchyma and xylary fibers are enriched in xylans. These data explain both a structural (hooked trichomes) and compositional (de-esterified pectins) for the ability of bedstraw to stick to other objects. The lightweight (achieved by a hollow pith) and elastic (achieved by strong xylary fibers and collenchyma surrounded by pectins) stems allow the bedstraws to ascend on other plants and scramble freely.