Physiology of the Cell Surface of Neurospora Ascospores. III. Distinction Between the Adsorptive and Entrance Phases of Cation Uptake

SUMMARY

The germination of ascospores of Neurospora tetrasperma has been shown to be inhibited by continual incubation in very small amounts of metal cations. Of these, Ag⁺, and p-chloromercuribenzoic acid (PCB) are the most toxic. Furthermore, these cations were shown to be adsorbed to the surface of the dormant ascospore from where they can penetrate to affect sensitive loci within or upon the surface of the cell. Cations like Ag⁺, Cu⁺⁺ and UO₂⁺⁺ can be taken up in sufficient quantity by the dormant cell so that germination is inhibited, even when the activated cells are incubated in distilled water. On the other hand, cations like Th⁺⁺⁺⁺ and Al⁺⁺⁺ do not inhibit under the latter conditions despite the fact that they are bound to the cell surface and are quite toxic when continually incubated with the germinating ascospore. These experiments support the idea that the dormant cell is impermeable to cations whereas this barrier is raised when germination is induced. Although, in a general way, the toxicity of some of the metals tested varies directly as a function of the insolubility of their mercaptide, the slope of the curve does not agree with that found by Shaw for other organisms.