Developmental and Structural Section
Spicer , Rachel , Tisdale-Orr, Tracy .
Auxin response and transport during the initiation of secondary growth in Populus.
The plant hormone auxin (indole-3-acetic acid) is a master regulator of plant morphology, but despite its prominent role in vascularization and apical dominance, little is known about the role of auxin in woody plant development. We sought to visualize auxin response in a woody stem during the transition from primary to secondary growth by developing several transgenic lines of Populus tremula x alba expressing GUS under the control of the synthetic auxin-responsive promoter DR5. Exogenous application of both auxin and the auxin transport inhibitor NPA induced significant GUS expression, with the latter occurring above the point of NPA application. GUS expression patterns in untreated pDR5-GUS Populus suggest that two separate routes of basipetal auxin transport exist in young woody stems, one formed by the primary xylem parenchyma of leaf traces, and one formed by the vascular cambium. Further up the stem, just beneath the shoot apex and before the appearance of a unified vascular cambium, GUS expression occurred in arcs of developing primary xylem. Current work is focused on improving methods of tissue preservation and sectioning of the vascular cambium to determine if the GUS expression is in fact restricted to cambial initials, or if it is instead concentrated in expanding xylem. The latter observation would be consistent with the GUS expression in the expanding primary xylem above, as well as a well-documented role of auxin in developing vasculature. However, current published measurements of auxin quantified by mass spectrometry suggest high concentrations in the vascular cambium itself. Transport assays with radiolabeled auxin confirmed the existence of two routes of basipetal auxin transport, an outer route near the vascular cambium and an inner route via the primary xylem parenchyma. Future work will focus on combining visualization of the auxin response in pDR5-GUS Populus with radiolabeled auxin transport assays to determine the route of auxin transport from the developing leaves into the nascent vascular cambium and/or the expanding vessel elements.
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1 - Connecticut College, Department of Botany, 270 Mohegan Avenue, New London, CT, 06320, USA
2 - Harvard University, Rowland Institute, 100 Edwin H. Land Boulevard, Cambridge, MA, 02142, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Waterman Room/Chase Park Plaza
Date: Tuesday, July 12th, 2011
Time: 9:00 AM