. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CALCIUM AND CELL POLARIZATION until germination does it accumulate at the rhizoid site. However, this may only indicate that CTC fluorescence does not reflect the pertinent Ca:+ pool within the cell, , the free, cytoplasmic Ca2+. To date, other probes spe- cific for cytoplasmic Ca2+ have not been used to investi- gate the Ca2+ distribution during axis formation in either Fiicus or Pelvetin. Externally imposed gradients have also been used to investigate the role of Ca:+ in early development. Pel- vet ia zygotes grown in
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CALCIUM AND CELL POLARIZATION until germination does it accumulate at the rhizoid site. However, this may only indicate that CTC fluorescence does not reflect the pertinent Ca:+ pool within the cell, , the free, cytoplasmic Ca2+. To date, other probes spe- cific for cytoplasmic Ca2+ have not been used to investi- gate the Ca2+ distribution during axis formation in either Fiicus or Pelvetin. Externally imposed gradients have also been used to investigate the role of Ca:+ in early development. Pel- vet ia zygotes grown in the presence of a gradient of CaCl: or of the Ca24-ionophore A23187 form rhizoids toward the more concentrated end of the gradient (Robinson and Jaffe, 1976; Robinson and Cone, 1980). This sug- gests that an induced cytoplasmic Ca2+ gradient is suffi- cient to orient the axis. However, at least 15 other exter- nal gradients also polarize fucoid zygotes (Jaffe, 1968). In the context of ionic currents, I find it most intriguing that zygotes germinate on the high side of imposed pH and K" gradients (Jaffe, 1968), yet the role of these ions in polarization has not been fully investigated. Whether all the imposed gradients act via a common mechanism, and whether that mechanism involves Ca2+, is unclear. In my opinion, the results discussed above do not pro- vide a clear picture of the role of calcium in polarization. A Ca2+ current begins to flow at the time of axis forma- tion, but there is no direct evidence that an internal gra- dient is generated. If a cytoplasmic gradient is essential for axis formation, then zygotes must be able to establish it in the absence of Ca2+ influx, and presumably in the absence of a transcellular Ca2+ current. Although growth in external Ca2+ and A23187 gradients can be expected to generate cytoplasmic Ca2+ gradients, the significance of the polarization induced under these conditions is tempered by the observation that other ionic gradients are
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
