Inositol hexakisphosphate mobilizes an endomembrane store of calcium in guard cells.

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 InsP6 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.

Elemental propagation of calcium signals in response-specific patterns determined by environmental stimulus strength.

Plant cells can respond qualitatively and quantitatively to a wide range of environmental signals. Ca(2+) is used as an intracellular signal for volume regulation in response to external osmotic changes. We show here that the spatiotemporal patterns of hypo-osmotically induced Ca(2+) signals vary dramatically with stimulus strength in embryonic cells of the marine alga Fucus.

Regulation of channel activity underlying cell volume and polarity signals in Fucus.

Polarized zygotes of the marine alga Fucus have been used to investigate the spatial control of Ca(2+) signals in a plant cell during apical growth and cell volume regulation in response to external osmotic fluctuations. UV laser microsurgery has been refined to enable plasma membrane patch clamp recordings from localized regions of the polarizing or polarized zygote. A plasma membrane cation channel that is mechanosensitive and significantly permeable to Ca(2+) was characterized in cell-attached and excised patch configurations.

Spatial Organization of Calcium Signaling Involved in Cell Volume Control in the Fucus Rhizoid.

Subprotoplasts prepared from different regions of rhizoid and thallus cells of Fucus zygotes displayed mechanosensitive plasma membrane channels in cell-attached patch-clamp experiments by using laser microsurgery. In excised patches, this channel was found to be voltage gated, carrying K+ outward and Ca2+ inward, with a relative permeability of Ca2+/K+ of 0.35 to 0.