Circadian clocks drive rhythms with a period near 24 h, but the molecular basis of the regulation of the period of the circadian clockis poorly understood. We previously demonstrated that metabolites affect the free-running period of the circadian oscillator of Arabidopsis (), with endogenous sugars acting as an accelerator and exogenous nicotinamide acting as a brake. Changes in circadian oscillator period are thought to adjust the timing of biological activities through the process of entrainment, in which the circadian oscillator becomes synchronized to rhythmic signals such as light and dark cycles as well as changes in internal metabolism. To identify the molecular components associated with the dynamic adjustment of circadian period, we performed a forward genetic screen. We identified Arabidopsis mutants that were either period insensitive to nicotinamide () or period oversensitive to nicotinamide (). We mapped to, a gene of unknown molecular function that was shown previously to play a role in light signaling. We found that has an early entrained phase, suggesting that the dynamic alteration of circadian period contributes to the correct timing of biological events. Our data provide insight into how the dynamic period adjustment of circadian oscillators contributes to establishing a correct phase relationship with the environment and show that BIG is involved in this process.
Hibiscus tiliaceus, locally known as Bhola was examined for phytochemical properties and its cytotoxic, antibacterial, analgesic and neuropharmacological activities using the ethanol extract of leaf and bark. The phytochemical analysis of the leaf extract indicated the presence of tannins, whereas bark extract indicated the presence of alkaloid, reducing sugar and tannins. A preliminary cytotoxicity of these extracts was determined by a simple and low cost assay using brine shrimp lethality. The leaf extract of the plant exhibited moderate cytotoxic effect (LC 50 : 20 µg/ml, LC 90 : 40 µg/ml) whereas the bark extract exhibited low cytotoxic effect (LC 50 : 50 µg/ml). In the analgesic test, the leaf extract showed comparatively high analgesic action than bark extract. There was no activity found in the leaf extract against the test bacterial strains, however bark extract exhibited a very little inhibitory effect on Staphylococcus aureus and Staphylococcus epidermidis. In the neuropharmacological test, the leaf and bark extract produced a decrease in both the time of onset of sleeping and the total sleeping time. The present study showed evidence that both leaf and bark extract of H. tiliaceus contain medicinally important bioactive compounds, thereby used as traditional medicine.
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