Figure 2.

Catabolism of exogenous pyrimidines by etiolated maize seedling tissue to release CO₂. Etiolated maize shoots were incubated in vials containing varying amounts of uracil (○), thymine (●), or dihydrouracil (□) at 30°C for 2 h. Each vial contained 0.4 μCi [2-¹⁴C]pyrimidine. The assays were quenched by injection of 4 n perchloric acid into the vial and the ¹⁴CO₂ released was trapped in a well containing 4 n KOH. The radioactivity in the wells was counted in a liquid scintillation counter to quantitate the amount of CO₂ released. Each point is the average of three replicates.