Fig 9.

Neurospora can modulate the K⁺ concentration dependence of growth rate and the substrate affinities of both K⁺ transporters. (A) Apparent dependence of specific growth rate upon the intracellular K⁺ concentration, early (1.5 h) and midway (4.5 h) in exponential growth. Parametric plot of data from Fig. 3; smooth curves were drawn by hand. (B and C) Net K⁺ fluxes plotted against extracellular K⁺ concentrations for cells growing exponentially after inoculation into Vogel's medium (K⁺-free) supplemented with 0.1 mM KCl. Initial values of [K⁺]_o at time 0 were greater than 0.1 mM due to loss of cellular K⁺ during the lag phase. [K⁺]_o was then gradually depleted by net uptake. Smooth curves were fitted to a Michaelis function having an offset concentration, 49.7 and 103.5 μM, respectively. Below the offset concentrations, steady fluxes were calculated as the average values out to 8 h: 9.04 and 3.26 mM/h, respectively.