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Abstract Detail



Physiological Section

Spicer, Rachel [1], Evanich, Daniel [2].

Basipetal auxin transport during secondary xylem development in Populus.

It is well established that polar auxin transport (PAT) – the directional, cell-to-cell transport of auxin mediated largely by the PIN proteins – is critical to vascular patterning in plants. In particular, PAT specifies the location of the procambium by channeling auxin into narrow files of cells in developing leaf primordia at the shoot apex. What is less clear, however, is what role auxin plays in and around the vascular cambium during secondary xylem development. Here we present the results of several experiments designed to characterize auxin transport in woody stems of Populus tremula x alba, including work using an auxin-responsive reporter construct (PtaDR5), several RNAi lines in which the expression of PtaPIN1 is reduced, and direct quantification of auxin via LC-MS/MS. GUS expression indicating an auxin response in PtaDR5 lines suggests that basipetal auxin transport through the procambium is continuous with auxin transport through the vascular cambium, as would be expected. Interestingly, despite the presence of 16 PIN proteins in Populus, reducing the expression of just one − PtaPIN1 − by 60-75% reduced the rate of auxin transport in woody stems by 55-65%. This confirms that basipetal transport in the cambial zone is mediated by the PIN proteins, and suggests that PtaPIN1 is important to this process. In addition to the cambial zone however, GUS expression in PtaDR5 lines shows an additional basipetal auxin stream moving through strands of primary xylem parenchyma surrounding the pith. These strands depart from the stem in a leaf trace, which led us to ask whether auxin might be produced by mature leaves and transported toward and/or into the stem. Application of the auxin transport inhibitor NPA to petioles reduced the auxin content proximal to the site of application by more than 50%, suggesting that indeed, PAT is occurring in the petioles, with auxin moving from the blade toward the stem. Interestingly however, defoliating plants failed to reduce the level of auxin in developing secondary xylem. Similarly, reducing the export of auxin from petioles by about 60% with NPA did not affect the level of auxin in developing secondary xylem or in strands of primary xylem parenchyma. It is thus unclear whether auxin transported in the petiole actually enters the stem, as well as where the auxin in primary xylem parenchyma is synthesized. This work suggests that auxin transport and biosynthesis in woody stems may be more complicated than once thought.


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1 - Connecticut College, Botany, 270 Mohegan Avenue, New London, CT, 06320, USA
2 - Connecticut College, Department Of Botany, 270 Mohegan Avenue, Campus Box 3531, New London, CT, 06320, USA

Keywords:
Populus
auxin
Wood
xylem
cambium.

Presentation Type: Oral Paper:Papers for Sections
Session: 53
Location: Salon 16/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 2:30 PM
Number: 53003
Abstract ID:1295
Candidate for Awards:None


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