Adenine salvage activity during callus induction and plant growth

Adenine phosphoribosyltransferase (APRT; EC 2.4.2.7) activity was monitored in crude extracts of Arabidopsis thaliana tissues and callus. Changes in APRT activity during germination were determined within different organs of the mature plant and during callus induction. APRT activity was constitutively expressed in all organs examined. There was an increase in APRT activity detected in seeds beginning 3 days following imbibition, after which the level decreased to that found in leaf tissue of mature plants. There was also an increase in APRT activity early during callus induction. A mutant that lacks APRT activity had a diminished capacity for callus induction in both the presence and absence of exogenous cytokinin. The results are consistent with the hypothesis that an increase in APRT activity is associated with actively dividing cells. The significance of these observations is discussed relative to the role of APRT in adenylate and cytokinin metabolism during plant development.