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Abstract Detail


Paleobotanical Section

Sanders, Heather [1], Rothwell, Gar W. [1], Wyatt, Sarah [1].

Upside down auxin suggests the evolutionary origin of isoetalean rhizomorphs.

Lycopsids, including quillworts and clubmosses, are the sister group of all other vascular plants. Paleozoic lycopsids included giant trees that consisted of an aerial and an underground shoot system (rhizomorph) that rooted the plant. In stems of vascular plants, and living lycopsids, the plant growth regulator auxin usually flows from the apex to the base of the shoot. Tracheary elements differentiate along a polar auxin transport (PAT) gradient. The direction of PAT is evidenced by the positions of swirled tracheary elements. When the flow of auxin through differentiating tracheary elements is disrupted by a branch or a node, the auxin pools and the tracheids differentiate in swirls. In stems of both seed plants and lycopsids, where PAT is basipetal, these circular tracheids occur immediately above branches or vascular traces (toward the shoot apex). The rhizomorph also produces swirls of tracheary elements that are a structural fingerprint for the direction of auxin transport. However, they occur away from the apex in the rhizomorph. The position of these swirled tracheids indicates that auxin is flowing backwards in this modified shoot system. Therefore, auxin flow is towards, not away from, the apex in the differentiating tracheary elements of the rhizomorph. This reversed directionality of PAT is correlated with the downward growth and the modification of the rhizomorph for rooting the plants.


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1 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA

Keywords:
auxin
lycopsid
rhizomorph
bipolar growth.

Presentation Type: Oral Paper:Papers for Sections
Session: CP11
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 11:45 AM
Number: CP11007
Abstract ID:1226


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