Hydrostatic pressure mimics gravitational pressure in characean cells.
Hydrostatic pressure applied to one end of a horizontal Chara cell induces a polarity of cytoplasmic streaming, thus mimicking the effect of gravity.  A positive hydrostatic pressure induces a more rapid streaming away from the applied pressure and a slower streaming toward the applied pressure.  In contrast, a negative pressure induces a more rapid streaming toward and a slower streaming away from the applied pressure.  Both the hydrostatic pressure-induced and gravity-induced polarity of cytoplasmic streaming respond identically to cell ligation, UV microbeam irradiation, external Ca2+ concentrations, osmotic pressure, neutral red, TEA Cl-, and the Ca2+ channel blockers nifedipine and LaCl3.  In addition, hydrostatic pressure applied to the bottom of a vertically-oriented cell can abolish and even reverse the gravity-induced polarity of cytoplasmic streaming.  These data indicate that both gravity and hydrostatic pressure act at the same point of the signal transduction chain leading to the induction of a polarity of cytoplasmic streaming and support the hypothesis that characean cells respond to gravity by sensing a gravity-induced pressure differential between the cell ends.
Staves
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MP
Section of Plant Biology, Cornell University, Ithaca, New York, USA.
Wayne
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R
Leopold
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AC
D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D016764:Cell Polarity; D000460:Chlorophyta / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003595:Cytoplasmic Streaming / Q000187:drug effects / Q000502:physiology*; D006112:Gravitation; D018466:Gravity Sensing / Q000187:drug effects / Q000502:physiology*; D006874:Hydrostatic Pressure; D007811:Lanthanum / Q000494:pharmacology; D008027:Light; D009499:Neutral Red / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D009997:Osmotic Pressure; D026902:Potassium Channel Blockers; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers; D013757:Tetraethylammonium Compounds; C028521:lanthanum chloride; D009499:Neutral Red; D019789:Tetraethylammonium; D007811:Lanthanum; D009543:Nifedipine; D002118:Calcium