Higher extracellular pH suppresses tracheary element differentiation by affecting auxin uptake

Naoki Shinohara, Munetaka Sugiyama, Hiroo Fukuda

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


In an optimized liquid medium containing auxin and cytokinin, mesophyll cells isolated from Zinnia elegans L. seedlings can be induced to differentiate into tracheary elements (TEs) at high frequency. However, it is known that buffering the medium at neutral pH severely suppresses TE differentiation. In the process of modifying the medium, we found that excessive administration of auxin restored the suppression. Based on this finding, we physiologically characterized auxin actions involved in TE differentiation by focusing on the influence of extracellular pH. First, dose/response relationships between auxin [1-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D)] concentrations and differentiated cell ratios were determined under various extracellular pH conditions. Secondly, intracellular concentrations of free forms and metabolites of auxin species were determined by analyzing extracts from cells cultured with radiolabeled NAA and 2,4-D under different extracellular pH conditions with liquid scintillation counting and thin-layer chromatography autoradiograms. Higher extracellular pH was found to reduce both the auxin potency for inducing TE differentiation and intracellular auxin accumulation. Reduction levels correlatively varied depending on the auxin species. These results suggest that the weakening in auxin potency at higher extracellular pH is ascribed to lower auxin uptake, which leads to decreased intracellular perception of the auxin signal. A model to predict auxin action that considers membrane transport, metabolism, and the perception of auxin is also presented.

Original languageEnglish
Pages (from-to)394-404
Number of pages11
Issue number2
Publication statusPublished - 2006 Jul
Externally publishedYes


  • Auxin
  • Extracellular pH
  • Membrane transport
  • Metabolism
  • Perception
  • Tracheary element differentiation

ASJC Scopus subject areas

  • Genetics
  • Plant Science


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