Sci. STKE, 26 August 2003
PLANT BIOLOGY IP6, Another Calcium Mobilizer
Inositol hexakisphosphate (IP6) is emerging as an intracellular signaling molecule in plants, yeast, and animals. In plants, IP6 increases in response to abscisic acid and contributes to the inhibition of a plasma membrane K+ current (IK,in) that leads to stomatal closure, which is the closure of a plasma membrane pore in plant guard cells to conserve water. Lemtiri-Chlieh et al. show that release of caged IP6 in guard cell protoplasts stimulated a transient increase in calcium concentration. IP6 did not stimulate the plasma membrane hyperpolarization-activated calcium current, and IP6-mediated inhibition of IK,in occurred in the absence of extracellular calcium. Thus, IP6 appears to stimulate a calcium transient through release from intracellular stores. In experiments with patch-clamped vacuoles, IP6 stimulated two conductances: the fast vacuolar (FV) conductance and a slow vacuolar (SV) conductance. Thus, IP6 appears able to mobilize calcium from the vacuole to create a calcium signal that contributes to osmoregulation in plants. It remains to be determined how IP6 mediates this effect-- whether there is an IP6 receptor that is a ligand-gated channel or whether IP6 contributes to calcium release through intermediates.
F. Lemtiri-Chlieh, E. A. MacRobbie, A. A. Webb, N. F. Manison, C. Brownlee, J. N. Skepper, J. Chen, G. D. Prestwich, C. A. Brearley, Inositol hexakisphosphate mobilizes an endomembrane store of calcium in guard cells. Proc. Natl. Acad. Sci. U.S.A. 100, 10091-10095 (2003). [Abstract] [Full Text]
Citation: IP6, Another Calcium Mobilizer. Sci. STKE 2003, tw334 (2003).
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