Endoplasmic reticulum,calciosomes and their possible roles in signal transduction

Summary Recent fluorescence, AVEC-DIC, and confocal laser scanning microscopic studies have revealed the dynamic nature and structural extent of a calcium-sequestering endoplasmic reticulum (ER) in plant cells. Various investigators have proposed different roles for the ER in cell motility. One, the ER plays a direct role in the generation of intracellular particle motions or two, the ER regulates particle motions indirectly. We show that the ER can be extruded fromAcetabularia cells, stains brightly with the fluorescent dye DiOC₆(3), and small (ca. 100 nm diameter) fluorescent vesicles are observed to move in or along the ER tubules. Intracellular particle movements in the giant algal cellAcetabularia can be transiently inhibited by IP₄, IP₃, and IP₂, compounds which in animal cells are known to cause the release of free calcium ions. A model is proposed which clarifies the possible relationships between the ER, calciosomes, calcium ions, and the microfilament-generated intracellular particle movements observed in plant cells.Abbreviations AVEC-DIC video microscopy in differential interference contrast - CFLSM confocal laser scanning microscope - DiOC₆(3) 3,3-dihexyloxacarbocyanine iodide - ER endoplasmic reticulum - IP₃ inositol triphosphate - N.A. numerical aperture - SIT silicon intensified target video camera - SR sarcoplasmic reticulum