Regulation of channel activity underlying cell volume and polarity signals in Fucus

Abstract

Polarized zygotes of the marine alga Fucus have been used to investigate the spatial control of Ca(2+) signals in a plant cell during apical growth and cell volume regulation in response to external osmotic fluctuations. UV laser microsurgery has been refined to enable plasma membrane patch clamp recordings from localized regions of the polarizing or polarized zygote. A plasma membrane cation channel that is mechanosensitive and significantly permeable to Ca(2+) was characterized in cell-attached and excised patch configurations. Parallel measurements of intracellular Ca(2+) using ratio photometric and imaging techniques were used to monitor temporal and spatial changes in cytoplasmic Ca(2+) (Ca(2+)(cyt)) in response to activation of these ion channels by osmotic swelling of the rhizoid. In polarized rhizoid cells spatial regulation of voltage- and mechanosensitive-Ca(2+) channels in the plasma membrane underlie changes in Ca(2+) that are crucial in signal-response transduction. Direct mechanical stimulation of channels in the plasma membrane of isolated sub-protoplasts from the apex of rhizoid cells can elicit changes in Ca(2+) in the underlying cytosol.

Cellular responses of developing Fucus serratus embryos exposed to elevated concentrations of Cu2+

“…Attenuation of the polar Ca 2+ signal by moderate [Cu 2+ ] ext may therefore on its own be sufficient to inhibit axis fixation and rhizoid elongation. Ion channel mediated Ca 2+ flux from the external medium into the cytoplasm is required for the growth related apical Ca 2+ elevation in Fucus rhizoids (Taylor et al 1996(Taylor et al , 1997. The inhibition of apical Ca 2+ elevations by Cu 2+ suggests an inhibition of channel-mediated Ca 2+ influx as one of the early effects of Cu 2+ .…”

“…Attenuation of the polar Ca 2+ signal by moderate [Cu 2+ ] ext may therefore on its own be sufficient to inhibit axis fixation and rhizoid elongation. Ion channel mediated Ca 2+ flux from the external medium into the cytoplasm is required for the growth related apical Ca 2+ elevation in Fucus rhizoids (Taylor et al . 1996, 1997).…”

“…Polarized signals underlying these localizations include localized Ca 2+ elevation at the rhizoid pole that is maintained, at least in part, by ion channel mediated influx of Ca 2+ across the plasma membrane (Taylor, Roberts & Brownlee 1992; Taylor & Brownlee 1993; Berger & Brownlee 1993; Roberts, Berger & Brownlee 1993; Taylor et al . 1996; Taylor, Manison & Brownlee 1997; Pu & Robinson 1998). The present study sets out to determine the susceptibility of different stages of Fucus zygote development to Cu 2+ exposure and to examine mechanisms of toxicity and tolerance.…”

Ion mapping in plant cells – methods and applications in signal transduction research

“…A tip-focused, steep gradient of cytoplasmic Ca 2+ is a common feature of such cells and has been imaged in pollen tubes (Fura-2-dextran, Pierson et al 1996), root hairs (confocal imaging with Indo-1, Wymer et al 1997), and Fucus rhizoid cells (confocal imaging with Calcium Green-dextran, Berger and Brownlee 1993). It derives from Ca 2+ entry via clustered Ca 2+ channels in the apical region of the plasma membrane (Pierson et al 1996;Taylor et al 1997;Wymer et al 1997) that acts in concert with unknown, endogenous polarity-determining factors . The apical Ca 2+ gradient, which is a prerequisite of directed growth (Malho et al 1995;Malho and Trewavas 1996;Trewavas and Malho 1997), shows characteristic oscillations that have been imaged with Fura-2 dextran (Franklin-Tong et al 1997).…”

Ion Fluxes and Modification of the Extracellular Matrix During Gamete Release in Fucoid Algae

“…Quantitative studies of K and Cl exchange between the receptacle and bulk medium to test this idea would be complicated by the two possible routes of flux (i.e. via the conceptacle pore and across the epidermis), but patch‐clamp electrophysiological approaches (Taylor et al 1997, Buchanan et al 2000) may be successful.…”