FREE CALCIUM IN MICRASTERIAS - LOCAL GRADIENTS ARE NOT DETECTED IN GROWING LOBES

Intracelluar free Ca2+ ([Ca2+]) has been measured in growing unicells of two species of the green alga, Micrasterias, which have been inject ed with the indicator dye fura-2-dextran, Ratiometric imaging of Micra sterias denticulata yields levels of 170 to 200 nM [Ca2+] but fails to reveal a significant [Ca2+] gradient associated with the tips of grow ing lobes, or in any other region of the cell, In Micrasterias muricat a slight elevations from a basal value of 350 to 500 nM have been obse rved, but these might be due to a general inward leakage of Ca2+ at th e plasma membrane which is enhanced at the narrow lobes of this cell b ecause of their greater relative surface to volume ratio, Experimental perturbation of the intracellular [Ca2+] with injection of the ion or the addition of the non-fluorescent ionophore, Br-A23187, reveal that [Ca2+] elevations can be generated and indicate that if they naturall y occurred, the image system would have detected them, Further evidenc e that [Ca2+] gradients are lacking derives from studies with BAPTA-ty pe buffers, Injection of 5,5'-dibromo BAPTA and 4,4'-difluoro BAPTA, w hich in several other systems are the most effective at dissipating in tracellular [Ca2+] gradients, have no effect on development of Micrast erias, Taken together, these studies indicate that lobe outgrowth in M icrasterias does not occur in association with marked localized [Ca2+] gradients.