Inositol hexakisphosphate mobilizes an endomembrane store of calcium in guard cells

Fouad Lemtiri-Chlieh, Enid A.C. MacRobbie, Alex A.R. Webb, Nick F. Manison, Colin Brownlee, Jeremy N. Skepper, Jian Chen, Glenn D. Prestwich, Charles A. Brearley*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

224 Scopus citations


myo-Inositol hexakisphosphate (InsP6) is the most abundant inositol phosphate in cells, yet it remains the most enigmatic of this class of signaling molecule. InsP6 plays a role in the processes by which the drought stress hormone abscisic acid (ABA) induces stomatal closure, conserving water and ensuring plant survival. Previous work has shown that InsP 6 levels in guard cells are elevated in response to ABA, and InsP6 inactivates the plasma membrane inward K+ conductance (IK,in) in a cytosolic calcium-dependent manner. The use of laser-scanning confocal microscopy in dye-loaded patch-clamped guard cell protoplasts shows that release of InsP6 from a caged precursor mobilizes calcium. Measurement of calcium (barium) currents ICa in patch-clamped protoplasts in whole cell mode shows that InsP6 has no effect on the calcium-permeable channels in the plasma membrane activated by ABA. The InsP6-mediated inhibition of IK,in can also be observed in the absence of external calcium. Thus the InsP6-induced increase in cytoplasmic calcium does not result from calcium influx but must arise from InsP6-triggered release of calcium from endomembrane stores. Measurements of vacuolar currents in patch-clamped isolated vacuoles in whole-vacuole mode showed that InsP6 activates both the fast and slow conductances of the guard cell vacuole. These data define InsP6 as an endomembrane-acting calcium-release signal in guard cells; the vacuole may contribute to InsP6-triggered Ca2+ release, but other endomembranes may also be involved.

Original languageEnglish (US)
Pages (from-to)10091-10095
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number17
StatePublished - Aug 19 2003
Externally publishedYes

ASJC Scopus subject areas

  • General


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