Cell cycle inhibitory effects of leaf extract from Curcuma vamana M. Sabu & Mangaly on mitotically synchronous cultures of Physarum polycephalum Schw.

Leaf extracts of C. vamana, endemic to Kerala state in India, were found to inhibit cell cycle progression in synchronous cultures of P. polycephalum in a concentration and phase-specific manner. Crude alkaloid extract (CAE) elicited maximum cell cycle delays in comparison to soxhletted chloroform, acetone and aqueous extracts. Total alkaloid content of CAE was found to be 64.9 mg/g. CAE showed lowest DPPH radical scavenging activity. Other extracts with higher free radical scavenging activity exhibited lesser cell cycle inhibiting potential. Upto 21% decrease in nuclear DNA was observed in CAE treated samples. However, genotoxicity as evidenced by comet assay was not observed. The extracts were also found to be non-toxic to human RBCs at the highest concentration tested (750 µg/mL). CAE treatment completely suppressed a 63 kDa polypeptide with a concomitant, but weak induction of a 60 kDa polypeptide suggesting that these may be cell cycle related. CAE was found to possess potent antiproliferative activity against PBLs. The study clearly demonstrates the cell cycle inhibitory activity of C. vamana leaf extracts, with CAE being the most potent of them.

Periodic events and cell cycle regulation in the plasmodia of Physarum polycephalum.

The multinucleated plasmodia of Physarum polycephalum, a myxomycete, have been extensively used in cell cycle studies. The natural synchrony of mitosis and DNA synthesis, easy culture methods, the ready fusions obtainable between plasmodia, and the amenability to phase specific studies, employing physical and chemical perturbers, are some of the attractive features of this organism. Because of the absence of a Gl phase in the plasmodia, there is a crowding of cell cycle specific marker events at the G2/M boundary, which reflect features of both the G2/M and the Gl/S boundaries of a typical eukaryotic cell. Prominent among these are the synthesis and overall activity of thymidine kinase, the co-triggering of tubulin and histone genes, translation of their mRNA, the organization and duplication of the microtubular organizing centres of the mitotic spindle and the triggering of cdc 2 kinase activity. These above events have not only served as good markers to monitor the progress of the plasmodial cell cycle, but have also been fairly thoroughly analysed by means of specific perturbers such as DNA synthesis inhibitors, antimicrotubular drugs, UV-irradiation, heat-shock etc. Along with fusion studies, these perturbation studies have been helpful in the formulation of various models on regulation of mitosis. These above aspects as well as prospects for future studies employing this organism are discussed.

Synthesis of actinomycin-insensitive RNA during the first postirradiation mitotic cycle, in the synchronously mitotic plasmodia of Physarum polycephalum.

A sucrose density gradient analysis of 3H-uridine pulse-labelled RNA from the first postirradiation mitotic cycle of Physarum polycephalum shows that all the density classes of RNA synthesized during this period are resistant to the peptide-antibiotic, actinomycin D. In fact, the synthesis is found to be greater in the presence of the drug. The heterogenously sedimenting synthetic activity here may represent a single species of RNA and its precursors or more than one kind of RNA. Further characterization of this RNA is meaningful in view of the actinomycin insensitivity of the postirradiation mitotic cycle itself to this antibiotic.