Ar. Taylor et al., SPATIAL-ORGANIZATION OF CALCIUM SIGNALING INVOLVED IN CELL-VOLUME CONTROL IN THE FUCUS RHIZOID, The Plant cell, 8(11), 1996, pp. 2015-2031
Subprotoplasts prepared from different regions of rhizoid and thallus
cells of Fucus zygotes displayed mechanosensitive plasma membrane chan
nels in cell-attached patch-clamp experiments by using laser microsurg
ery. In excised patches, this channel was found to be voltage gated, c
arrying K+ outward and Ca2+ inward, with a relative permeability of Ca
2+/K+ of 0.35 to 0.5, and an increased open probability at membrane po
tentials more positive than -80 mv. No significant difference was foun
d in the density of this channel type from different regions of rhizoi
d or thallus cells. Hypoosmotic treatment of intact zygotes induced dr
amatic transient elevations of cytoplasmic Ca2+, initiating at the rhi
zoid apex and propagating in a wavelike manner to subapical regions. L
ocalized initiation of the Ca2+ transient correlated with greater osmo
tic swelling at the rhizoid apex compared with other regions of the zy
gote. Ca2+ transients exhibited a refractory period between successive
hypoosmotic shocks, during which additional transients could not be e
licited and the ability to osmoregulate was impaired. Buffering the Ca
2+ transients with microinjected Br(2)BAPTA similarly reduced the abil
ity of rhizoid cells to osmoregulate. Ca2+ influx was associated with
the initiation of the Ca2+ transient in apical regions, whereas intrac
ellular sources contributed to its propagation. Thus, localized signal
transduction is patterned by interactions of the cell wall, plasma me
mbrane, and intracellular Ca2+ stores.