Abstract Detail

Physiological Section

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

Partial defoliation suggests that mature leaves contribute to the basipetal auxin stream in woody Populus stems.

Knowledge of whole-plant auxin dynamics is important for our understanding of many processes critical to plant growth and development.  Aboveground auxin biosynthesis is currently thought to be restricted to the shoot apex, where auxin is then transported down (i.e., basipetally) through developing vasculature into the stem.  In woody plants, this basipetal auxin transport continues in mature stems through the cambial region and developing secondary xylem.  Regarding the shoot tip as the sole site of auxin biosynthesis is problematic when one considers large woody plants, which maintain relatively constant auxin concentrations along the entire length of the stem despite an increase in diameter.  In addition, earlier work in pea plants using a combination of deuterium labeling and defoliation showed that mature leaves have the capacity to synthesize auxin and that their removal reduces stem auxin content.  Here we present evidence in the model system Populus that mature leaves may contribute to the basipetal auxin stream in the stem.  Three-month-old Populus tremula x alba plants grown in a greenhouse were defoliated starting at the eighth leaf beneath the apex (defined as the cluster of tightly spaced developing leaves at the tip), leaving the apex and seven expanding leaves intact.  Apices and developing xylem were then collected 48 hours after defoliation, with the latter obtained by removing the outer bark and scraping the length of the exposed stem with a razor blade.  Tissues were homogenized following the addition of a known quantity of ¹³C-labeled auxin (i.e., an internal standard) and extracts were purified by SPE and methylated.  Auxin (specifically, the methyl ester of indole-3-acetic acid) was then quantified via LC-MS/MS.  The auxin content of developing xylem was reduced by about 40% in defoliated plants relative to controls (p-value < 0.01, two-tailed t-test).  In contrast, there was no significant reduction in the auxin content of apices (p-value = 0.2).  Current work in the lab is focused on determining the route that leaf-derived auxin may take to enter the stem.  Specifically, petiolar application of the auxin transport inhibitor NPA and phloem-loading of the symplasmic tracer CFDA are being used to determine whether auxin movement out of the leaf is via polar auxin transport or via bulk flow through the phloem.

1 - Connecticut College, Botany Department, 270 Mohegan Avenue, New London, CT, 06320, USA
2 - Connecticut College, Biology Department, 270 Mohegan Avenue, New London, CT, 06320, USA

Keywords:
auxin
Populus
xylem.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Eyrie/Boise Centre
Date: Monday, July 28th, 2014
Time: 5:30 PM
Number: PPS004
Abstract ID:764
Candidate for Awards:Physiological Section Best poster presentation