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Higher extracellular pH suppresses tracheary element differentiation by affecting auxin uptake
Naoki Shinohara1, Munetaka Sugiyama, Hiroo Fukuda
1Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo, 113-0033 Tokyo, Japan. shino@biol.s.u-tokyo.ac.jp
Planta
|February 2, 2006
Summary
Extracellular pH influences plant cell differentiation. Higher pH reduces auxin uptake, decreasing tracheary element differentiation in Zinnia elegans, suggesting pH-dependent auxin signaling is crucial.
Area of Science:
- Plant developmental biology
- Plant physiology
- Cell biology
Background:
- Mesophyll cells from Zinnia elegans can differentiate into tracheary elements (TEs) in vitro with auxin and cytokinin.
- Neutral pH significantly suppresses TE differentiation, but high auxin levels can overcome this suppression.
- Understanding the role of extracellular pH in auxin-mediated TE differentiation is critical.
Purpose of the Study:
- To physiologically characterize auxin actions in TE differentiation under varying extracellular pH.
- To investigate the influence of extracellular pH on auxin uptake, metabolism, and signaling.
Main Methods:
- Determined dose/response relationships of auxin concentrations (NAA, 2,4-D) and TE differentiation ratios at different pH.
- Quantified intracellular auxin concentrations (free and metabolized forms) using radiolabeled auxins.
- Employed liquid scintillation counting and thin-layer chromatography autoradiography for auxin analysis.
Main Results:
- Elevated extracellular pH reduced auxin potency for TE differentiation and decreased intracellular auxin accumulation.
- Auxin uptake and signaling were found to be pH-dependent, with variations between auxin species.
- Higher pH led to lower auxin uptake, resulting in diminished intracellular auxin signal perception.
Conclusions:
- Extracellular pH significantly impacts auxin's ability to induce TE differentiation in Zinnia elegans.
- Reduced auxin uptake at higher pH is the primary mechanism weakening auxin potency.
- A model for auxin action incorporating membrane transport, metabolism, and perception is proposed.
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