Fig. 1. Generation of superoxide during early development. (A) Ax2 cells were starved after plating onto plastic dishes under buffer at a density of 1.4x10⁶ cells/cm², and superoxide generation was measured using the XTT assay. The increase in optical density results from the accumulation of the brightly coloured product of the reaction of XTT and superoxide. XTT reduction in the absence of cells was subtracted from each time point. Data are the means ± s.d. of five experiments. (B) Ax2 cells were starved in shaking suspension at a density of 2x10⁷ cells/ml in the presence () and absence () of 100 units/ml Cu/Zn SOD. Data are the means ± s.d. of three experiments. (C) Ax2 cells were developed exactly as for A but with the addition of various concentrations of sodium diethyldithiocarbamate (DEDTC). The absorbance was measured after 7 hours. The data are expressed relative to the control lacking DEDTC, and are the means ± s.e.m. of three experiments.