A deficiency of hypoxanthine phosphoribosyltransferase in a sycamore callus resistant to azaguanine.

Sycamore (Acer pseudoplatanus L.) calluses resistant to azaguanine were isolated after mutagenesis with nitrosoguanidine. One callus SNC61 was highly variable in its growth on 10 μg/ml azaguanine and it was concluded that its resistance was not due to a stable alteration in the callus. Another callus SNE31 was isolated after 4.5 months culture in 0.5 or 1 μg/ml azaguanine which had a 10-fold increase in resistance to azaguanine. This was shown to be accompanied by a reduction to 50% of the normal level of hypoxanthine phosphoribosyltransferase (E.C.2.4.2.8).