Melatonin application differentially modulates the enzymes associated with antioxidative machinery and ascorbate-glutathione cycle during arsenate exposure in indica rice varieties.

Arsenic (As) contamination and accumulation in rice is a serious concern causing severe oxidative damage. Melatonin acts as a protective agent in plant defence against multiple abiotic stresses. The mechanism of antioxidant function of melatonin during As stress in rice genotypes is less studied. In this study, hydroponically-grown As-susceptible (Khitish) and As-tolerant (Muktashri) rice cultivars, subjected to 150 µm arsenate stress, were supplemented with exogenously applied melatonin (20 µm) to examine the plant defence mechanism. Melatonin (Mel) increased root and shoot length, fresh and dry weight, chlorophyll a and b content and activated reducing power and free radical scavenging capacity in both rice cultivars. The role of Mel in the sensitive variety appeared to be more prominent with respect to reduced water saturation deficit by reducing endogenous As and H2 O2 accumulation, and enhancing overall antioxidant capacity by imposing reduced requirement of catalase for ROS detoxification, and restoring As-inhibited activity of glutathione-S-transferase, glutathione peroxidase and dehydroascorbate reductase. In contrast, melatonin treatment in the tolerant cultivar required reduced involvement of ascorbate peroxidase to deal with As toxicity, and complemented the stress-mediated inhibition of guaiacol peroxidase activity. Isozyme profiling also established extensive varietal differences with regard to induction of new isoform(s) by Mel during As treatment. This study provides clear insights into mechanistic details of the regulation of antioxidative enzymes by melatonin in contrasting rice genotypes, which may prove helpful in generating As tolerance in susceptible rice varieties grown in marginalized soils, thereby improving crop yield and productivity.

Transmigrated mandibular permanent canine: a case report.

A case of transmigration of mandibular canine is presented. The importance of anesthetizing the transmigrated tooth from the side of origin is highlighted.

Dietary garlic extract in modifying clastogenic effects of inorganic arsenic in mice: two-generation studies.

Mice are fed by gavage crude garlic extract (100 mg/kg b.wt.) for 30 consecutive days. One set was administered sodium arsenite (0.1 mg/kg b.wt.) simultaneously. Another set was treated with sodium arsenite only. Mice given distilled water were kept as negative control. Exposed mice from each set were sacrificed and bone marrow preparations examined for chromosomal aberrations and damaged cells. Sodium arsenite is a strong clastogen and the effects were reduced to a significant level by prolonged administration of garlic extract. For F1 studies, exposed male mice were mated with exposed female mice, and the progeny examined. In the progeny, clastogenic effects of sodium arsenite persisted in a lower degree, indicating that the metal is able to cross the transplacental barrier. There was no statistically significant difference between the effect in progeny of parents only given sodium arsenite when given simultaneously for prolonged periods in the parents; however, the effect is meagre in the next generation.

Modification of clastogenicity of three known clastogens by garlic extract in mice in vivo.

The anticlastogenic activity of crude extract of garlic (Allium sativum L.) was studied in bone marrow cells of mice. Male laboratory-bred Swiss albino mice were given one of three concentrations of the freshly prepared extract (100 mg, 50 mg, and 25 mg/kg body weight) as a dietary supplement by gavage for 6 consecutive days. On the seventh day the mice were administered a single acute dose of two known clastogens, mitomycin C(1.5 mg/kg) and cyclophosphamide (25 mg/kg) or sodium arsenite (2.5 mg/kg), simultaneously with garlic extract. After 24 hr, chromosome preparations were made from the bone marrow cells. The endpoint studied were chromosomal aberrations and damaged cells. Garlic extract alone induced a low level of chromosomal damage. The clastogenicity of all three mutagens were reduced significantly in the animals which had been given garlic extract as dietary supplement. The extent of reduction was different for the three clastogens and may be attributed to the interaction with the different components of the extract.