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 (I_K,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 I_K,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]

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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, and Charles A. Brearley (19 August 2003)
PNAS 100 (17), 10091. [DOI: 10.1073/pnas.1133289100]
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