Osmotic calcium signalling in Fucus embryos

Abstract

Fucoid algae grow in the intertidal region where they experience dramatic daily
fluctuations in external salinity. Tolerance to hypo-osmotic shocks in Fucus
embryos is greatest in species that live higher up the shore and varies with the
age of the embryo. The polarized rhizoid cell of the Fucus embryo provides a useful system for determining the propagation of Ca²⁺ signals in response to
osmotic stress. Treatment with relatively small hypo-osmotic shocks caused
elevations of Ca²⁺ that were restricted to rhizoid apices. Treatment with more
severe hypo-osmotic shocks caused Ca²⁺ elevations that propagated as waves in
sub-apical regions of cells. The pattern of apical and perinuclear Ca²⁺ signals
correlated well with endoplasmic reticulum-rich regions of the, largely vacuole-free, rhizoid cell. An increase of Ca²⁺ in the nuclear region only, caused a slowing of the rhizoid cell cycle, whilst an apical Ca²⁺ elevation only, caused a reduction in cell volume. It thus appears that specificity of response can be encoded in the spatiotemporal pattern of the Ca²⁺ signal. Mitochondria appeared to function as spatial buffers that restricted the passage of small apical Ca²⁺ elevations. Detailed analysis of propagating Ca²⁺ signals revealed the presence of
unitary Ca²⁺ elevations at the wavefront. Ins(1,4,5)P_3-induced and osmotically-induced Ca²⁺ events did not differ significantly in amplitude or spatial dimensions. Ca²⁺ elevations at the apex corresponded to sites where the plasma
membrane was in close contact with the cell wall and that were rich in actin.
Specific inhibitors of actin dynamics, such as cytochalasin D, abolished these
localized Ca²⁺ elevations which was consistent with a role for actin in the
maintenance of the apical Ca²⁺ gradient possibly through regulation of Ca²⁺-
permeable ion channels. The presence in the rhizoid cell of a mechanical and an
osmotic sensor have been determined.

Date of Award	Apr 2001
Original language	English
Awarding Institution	University of Wales, Bangor
Sponsors	Sir William Roberts Scholarship & The Laboratory, Marine Biological Association of the United Kingdom
Supervisor	Deri Tomos (Supervisor)