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

Abstract

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 0.5, and an increased open probability at membrane potentials more positive than -80 mV. No significant difference was found in the density of this channel type from different regions of rhizoid or thallus cells. Hypoosmotic treatment of intact zygotes induced dramatic transient elevations of cytoplasmic Ca2+, initiating at the rhizoid apex and propagating in a wavelike manner to subapical regions. Localized initiation of the Ca2+ transient correlated with greater osmotic swelling at the rhizoid apex compared with other regions of the zygote. Ca2+ transients exhibited a refractory period between successive hypoosmotic shocks, during which additional transients could not be elicited and the ability to osmoregulate was impaired. Buffering the Ca2+ transients with microinjected Br2BAPTA similarly reduced the ability of rhizoid cells to osmoregulate. Ca2+ influx was associated with the initiation of the Ca2+ transient in apical regions, whereas intracellular sources contributed to its propagation. Thus, localized signal transduction is patterned by interactions of the cell wall, plasma membrane, and intracellular Ca2+ stores.

Calcium signaling in plants

“…The spatial and temporal characteristics were strikingly similar to those observed in animal cells during fertilization. It is clear that the interaction between gametes during reproduction in higher plants involves dynamic changes in [Ca 2 + ] i , a situation that has been observed for algae [75,76], sea urchins [77] and mammals [78]. The spatial and temporal characteristics of these increases vary to some extent, though they all appear to take the form of a Ca 2 + wave across the cell, originating from the point of fertilization.…”

“…In this way, the response of a cell may be integrated using information from a single message (the original point source of Ca 2 + ). Ca 2 + waves appear to be a distinctive feature of fertilization, in animal cells [96], algal cells [76] and plant cells [74]. This may be a characteristic 'Ca 2 + signature' evoked by the fertilization event, with increases in Ca 2 + propagating from the point of initial fertilization across the cell.…”

A tip-high, Ca2+-interdependent, reactive oxygen species gradient is associated with polarized growth in Fucus serratus zygotes

“…BrieXy, for microinjection zygotes were superfused with 0.1 M sorbitol to reduce internal turgor pressure and dyes (1 mM in artiWcial intracellular solution, 200 mM KCl, 10 mM Hepes, 550 mM mannitol, pH 7.0) were pressure microinjected to a Wnal intracellular concentration of 10-50 M, using dry bevelled pipettes fabricated from 1.2 mm Wlamented borosilicate glass (Taylor et al 1996).…”

Fusion and fission of plasma-membrane material accommodates for osmotically induced changes in the surface area of guard-cell protoplasts

“…Kell and Glaser (1993) have postulated that a transient increase in cytosolic Ca 2+ occurs during membrane expansion, which in turn may stimulates exocytosis. Indeed, an increase in cytosolic Ca 2+ has been observed upon hypoosmotic shock of Fucus (Taylor et al 1996) and Lamprothamnium (Okazaki et al 1987). A plausible link between membrane tension during hypoosmotic shock and an increase in cytosolic Ca 2+ may be provided by mechanosensitive Ca 2+ -permeable ion channels (SA Ca 2+ channels), which have been described in the plasma membrane of guard cells of Vicia faba (Cosgrove and Hedrich 1991).…”