BIG Regulates Dynamic Adjustment of Circadian Period in Arabidopsis thaliana

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 (Arabidopsis thaliana), 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 (sin) or period oversensitive to nicotinamide (son). We mapped son1 to BIG, a gene of unknown molecular function that was shown previously to play a role in light signaling. We found that son1 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.

Evaluation of pharmacological activity of Hibiscus tiliaceus

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 (LC50: 20 µg/ml, LC90: 40 µg/ml) whereas the bark extract exhibited low cytotoxic effect (LC50: 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.

NO-Mediated [Ca2+]cyt Increases Depend on ADP-Ribosyl Cyclase Activity in Arabidopsis

Cyclic ADP ribose (cADPR) is a Ca(2+)-mobilizing intracellular second messenger synthesized from NAD by ADP-ribosyl cyclases (ADPR cyclases). In animals, cADPR targets the ryanodine receptor present in the sarcoplasmic/endoplasmic reticulum to promote Ca(2+) release from intracellular stores to increase the concentration of cytosolic free Ca(2+) in Arabidopsis (Arabidopsis thaliana), and cADPR has been proposed to play a central role in signal transduction pathways evoked by the drought and stress hormone, abscisic acid, and the circadian clock. Despite evidence for the action of cADPR in Arabidopsis, no predicted proteins with significant similarity to the known ADPR cyclases have been reported in any plant genome database, suggesting either that there is a unique route for cADPR synthesis or that a homolog of ADPR cyclase with low similarity might exist in plants. We sought to determine whether the low levels of ADPR cyclase activity reported in Arabidopsis are indicative of a bona fide activity that can be associated with the regulation of Ca(2+) signaling. We adapted two different fluorescence-based assays to measure ADPR cyclase activity in Arabidopsis and found that this activity has the characteristics of a nucleotide cyclase that is activated by nitric oxide to increase cADPR and mobilize Ca(2.)