Effect of OA-inhibitor of protein phosphatases PP1 and PP2A — on initiation of DNA replication and mitosis in Vicia faba root meristems

According to the principal control point (PCP) hypothesis, experiments with excised, carbohydrate-starved stationary root meristems of Vicia faba var. minor have demonstrated that cells which previously divided asynchronously were preferentially blocked in G1 (PCP1) and G2 (PCP2) phases. When stationary phase meristems are supplied with exogenous carbohydrate (2 % sucrose), the G1- and G2-arrested cells start out DNA replication and mitotic divisions, respectively. The resumption of DNA synthesis and mitosis is not immediate and the delays of G1- and G2-arrested cells are found different. Using this model, we examined the effects of 4 pulse incubations with okadaic acid (OA), a specific inhibitor of PP1 and PP2A, on the duration of intervals elapsing between the provision of sucrose and the first appearance of S- and M-phase cells. We have found that depending on the period during which OA had been applied, the release from G1 and G2 phase arrest-points becomes prolonged, showing different time-course modifications. The obtained data provide evidence that activation of PP1 and PP2A is required to allow the cells for both PCP1→S and PCP2→M transitions in root meristems of V. faba.