Skip to main content
PMC home page
Plant Physiology logoLink to Plant Physiology
. 1997 Feb;113(2):559–573. doi: 10.1104/pp.113.2.559

Xylem Sap pH Increase: A Drought Signal Received at the Apoplastic Face of the Guard Cell That Involves the Suppression of Saturable Abscisic Acid Uptake by the Epidermal Symplast.

S Wilkinson 1, W J Davies 1
PMCID: PMC158172  PMID: 12223626

Abstract

Drought increased the pH of Commelina communis xylem sap from 6.1 to 6.7. Conductances of transpiring leaves were 50% lower in pH 7.0 than in pH 6.0 buffers, but bulk leaf abscisic acid (ABA) concentration and shoot water status were unaffected by pH. Stomatal apertures of isolated abaxial epidermis incubated on simple buffers increased with external pH, so in vivo this must be overridden by alternative pH effects. Reductions in leaf transpiration rate at pH 7.0 were dependent on the presence of 10-8 mol dm-3 ABA in the xylem stream. We inferred that at pH 7.0 leaf apoplastic ABA concentrations increased: pH did not affect distributions of ABA among leaf tissues, but isolated epidermis and mesophyll tissue took up more 3H-ABA from pH 6.0 than from pH 7.0 buffers. The apoplastic ABA increase at pH 7.0 may result from reduced symplastic sequestration. A portion of 3H-ABA uptake by the epidermis was saturable at pH 6.0 but not at pH 7.0. An ABA uptake carrier may contribute to ABA sequestration by the leaf symplast of well-watered plants, and its inactivity at pH 7.0 may favor apoplastic ABA accumulation in draughted plants. Effects of external pH on stomatal apertures in the isolated epidermis indicate that published data supporting a role for internal guard cell ABA receptors should be reassessed.

Full Text

The Full Text of this article is available as a PDF (1.5 MB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Anderson B. E., Ward J. M., Schroeder J. I. Evidence for an Extracellular Reception Site for Abscisic Acid in Commelina Guard Cells. Plant Physiol. 1994 Apr;104(4):1177–1183. doi: 10.1104/pp.104.4.1177. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Assmann S. M. Signal transduction in guard cells. Annu Rev Cell Biol. 1993;9:345–375. doi: 10.1146/annurev.cb.09.110193.002021. [DOI] [PubMed] [Google Scholar]
  3. Bianco-Colomas J., Barthe P., Orlandini M., Le Page-Degivry M. T. Carrier-Mediated Uptake of Abscisic Acid by Suspension-Cultured Amaranthus tricolor Cells. Plant Physiol. 1991 Apr;95(4):990–996. doi: 10.1104/pp.95.4.990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Cornish K., Zeevaart J. A. Movement of Abscisic Acid into the Apoplast in Response to Water Stress in Xanthium strumarium L. Plant Physiol. 1985 Jul;78(3):623–626. doi: 10.1104/pp.78.3.623. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Hartung W., Radin J. W., Hendrix D. L. Abscisic Acid Movement into the Apoplastic solution of Water-Stressed Cotton Leaves: Role of Apoplastic pH. Plant Physiol. 1988 Mar;86(3):908–913. doi: 10.1104/pp.86.3.908. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Ilan N., Schwartz A., Moran N. External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba. J Gen Physiol. 1994 May;103(5):807–831. doi: 10.1085/jgp.103.5.807. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Kaiser W. M., Hartung W. Uptake and Release of Abscisic Acid by Isolated Photoautotrophic Mesophyll Cells, Depending on pH Gradients. Plant Physiol. 1981 Jul;68(1):202–206. doi: 10.1104/pp.68.1.202. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Schwartz A., Wu W. H., Tucker E. B., Assmann S. M. Inhibition of inward K+ channels and stomatal response by abscisic acid: an intracellular locus of phytohormone action. Proc Natl Acad Sci U S A. 1994 Apr 26;91(9):4019–4023. doi: 10.1073/pnas.91.9.4019. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Stewart P. A. Modern quantitative acid-base chemistry. Can J Physiol Pharmacol. 1983 Dec;61(12):1444–1461. doi: 10.1139/y83-207. [DOI] [PubMed] [Google Scholar]
  10. Tardieu F., Davies W. J. Stomatal response to abscisic Acid is a function of current plant water status. Plant Physiol. 1992 Feb;98(2):540–545. doi: 10.1104/pp.98.2.540. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Trejo C. L., Clephan A. L., Davies W. J. How Do Stomata Read Abscisic Acid Signals? Plant Physiol. 1995 Nov;109(3):803–811. doi: 10.1104/pp.109.3.803. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Windsor M. L., Milborrow B. V., McFarlane I. J. The Uptake of (+)-S- and (-)-R-Abscisic Acid by Suspension Culture Cells of Hopbush (Dodonaea viscosa). Plant Physiol. 1992 Sep;100(1):54–62. doi: 10.1104/pp.100.1.54. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Plant Physiology are provided here courtesy of Oxford University Press

RESOURCES