Protein Phosphorylation During the Transitions from G1 Arrest Point to S and G2 Arrest Point to M in Vicia faba Root Meristem

Abstract

Using monoclonal FITC conjugated antibodies that specifically recognize phosphorylated form of threonine (α-TP-FITC) it was shown that in excised, sugar-starved root meristems of Vicia faba subsp. minor the expression of two principal control points (PCPs) is correlated with a marked decrease in nuclear and nucleolar phosphorylation of proteins. When stationary phase meristems are supplied with 2 % sucrose, the G1-arrested cells start out DNA replication (assessed by pulse 3H-thymidine labeling), while the cells blocked in G2 phase initiate mitotic divisions. Using this model, we have found that depending on the period during which the sucrose-mediated PCP1→S and PCP2→M transitions are affected by 6-dimethylaminopurine, an inhibitor of protein kinases, the release from G1 and G2 phase arrest-points of the cell cycle become prolonged, showing different time-course modifications. Furthermore, our results seem to implicate that both PCP1 and PCP2 comprise subpopulations of cells differing with respect to the rates at which they commence DNA replication and mitosis.