Calcium and morphogenetic fields.

Experiments on polarizing fucoid eggs indicate that they drive a steady calcium ion current through themselves as they establish a developmental axis. Moreover, the experiments strongly suggest that this current establishes a pCa gradient within the egg which is part of the mechanism which establishes this axis. It is suggested that Child's 'metabolic gradients' (as well as Bünning's unequal plant cell divisions) likewise include pCa gradients with Child's 'high' ends and Bünning's antimeristemoid ends being regions of low pCa. Evidence for other developmental calcium currents (obtained with a vibrating extracellular voltage electrode) is reviewed, and the development of a vibrating extracellular pCa electrode is proposed. Finally, progress towards direct observations of intracellular pCa gradients is reviewed. This includes visualization of an apparent steady high calcium cap at the vegetal (and perhaps, too, the animal) pole of medaka fish eggs with the aid of aequorin.