Participation of endomembrane cation/H+ exchanger AtCHX20 in osmoregulation of guard cells

Senthilkumar Padmanaban, Salil Chanroj, June M. Kwak, Xiyan Li, John M. Ward, Heven Sze

Research output: Contribution to journalArticle

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Abstract

Guard cell movement is induced by environmental and hormonal signals that cause changes in turgor through changes in uptake or release of solutes and water. Several transporters mediating these fluxes at the plasma membrane have been characterized; however, less is known about transport at endomembranes. CHX20, a member of a poorly understood cation/H+ exchanger gene family in Arabidopsis (Arabidopsis thaliana), is preferentially and highly expressed in guard cells as shown by promoter:: β-glucuronidase activity and by whole-genome microarray. Interestingly, three independent homozygous mutants carrying T-DNA insertions in CHX20 showed 35% reduction in light-induced stomatal opening compared to wild-type plants. To test the biochemical function of CHX20, cDNA was expressed in a yeast (Saccharomyces cerevisiae) mutant that lacks Na+(K+)/H+ antiporters (Δnhx1 Δnha1 Δkha1) and plasma membrane Na+ pumps (Δena1-4). Curiously, CHX20 did not enhance tolerance of mutants to moderate Na+ or high K+ stress. Instead, it restored growth of the mutant on medium with low K+ at slightly alkaline pH, but had no effect on growth at acidic pH. Green fluorescent protein-tagged CHX20 expressed in mesophyll protoplasts was localized mainly to membranes of the endosomal system. Furthermore, light-induced stomatal opening of the Arabidopsis mutants was insensitive to external pH and was impaired at high KCl. The results are consistent with the idea that, in exchanging K+ for H+, CHX20 maintains K+ homeostasis and influences pH under certain conditions. Together, these results provide genetic and biochemical evidence that one CHX protein plays a critical role in osmoregulation through K+ fluxes and possibly pH modulation of an active endomembrane system in guard cells.

Original languageEnglish (US)
Pages (from-to)82-93
Number of pages12
JournalPlant physiology
Volume144
Issue number1
DOIs
StatePublished - May 2007

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Osmoregulation
osmoregulation
guard cells
Cations
cations
mutants
Arabidopsis
plasma membrane
Cell Membrane
endomembrane system
Light
Sodium-Hydrogen Antiporter
Protoplasts
Glucuronidase
turgor
Growth
Green Fluorescent Proteins
green fluorescent protein
cell movement
pumps

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Participation of endomembrane cation/H+ exchanger AtCHX20 in osmoregulation of guard cells. / Padmanaban, Senthilkumar; Chanroj, Salil; Kwak, June M.; Li, Xiyan; Ward, John M.; Sze, Heven.

In: Plant physiology, Vol. 144, No. 1, 05.2007, p. 82-93.

Research output: Contribution to journalArticle

Padmanaban, Senthilkumar ; Chanroj, Salil ; Kwak, June M. ; Li, Xiyan ; Ward, John M. ; Sze, Heven. / Participation of endomembrane cation/H+ exchanger AtCHX20 in osmoregulation of guard cells. In: Plant physiology. 2007 ; Vol. 144, No. 1. pp. 82-93.
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