Distribution of ions inNeurospora crassa determined by quantitative electron microprobe analysis

Summary It was investigated whether the low membrane potential at the tip of hyphae ofNeurospora crassa could be described as a diffusion potential. The distribution of Na, K and P inNeurospora was measured by electron microprobe analysis of freeze-dried hyphae. Quantitative determinations were made with freeze-dried gelatin standards and with crystalline standards. The local concentrations of Na and K were in accordance with the theory that at the tip of the hyphe, these ions are distributed passively across the plasma membrane.