A Study of the Effect of Bulges on Bar Formation in Disk galaxies

We use N-body simulations of bar formation in isolated galaxies to study the effect of bulge mass and bulge concentration on bar formation. Bars are global disk instabilities that evolve by transferring angular momentum from the inner to outer disks and to the dark matter halo. It is well known that a massive spherical component such as halo in a disk galaxy can make it bar stable. In this study we explore the effect of another spherical component, the bulge, on bar formation in disk galaxies. In our models we vary both the bulge mass and concentration. We have used two sets of models, one that has a dense bulge and high surface density disk. The second model has a less concentrated bulge and a lighter disk. In both models we vary the bulge to disk mass fraction from 0 to 0.7. Simulations of both the models show that there is an upper cutoff in bulge to disk mass ratio M b /M d above which bars cannot form; the cutoff is smaller for denser bulges( M b /M d = 0.2) compared to less denser ones (M b /M d = 0.5). We define a new criteria for bar formation in terms of bulge to disk radial force ratio (F b /F d ) at the disk scale lengths above which bars cannot form. We find that if F b /F d > 0.35, a disk is stable and a bar cannot form. Our results indicate that early type disk galaxies can still form strong bars in spite of having massive bulges.Comment: Accepted at MNRAS,12 pages, 19 figure

Isolation and characterisation of endophytic bacteria present in the leaves of Glycosmis pentaphylla (Retz.) Correa

Endophytes are an endosymbiotic group of microorganisms that dwell in plant tissues and are reservoirs of bioactive compounds. However, the researches on this area are limited. The present investigation was undertaken to isolate and characterise endophytic bacteria from the leaves of Glycosmis pentaphylla (Retz.) Correa. An effective surface sterilisation procedure was developed from the experiment to isolate endophytic bacteria from the leaves of the candidate species. There was no bacterial growth observed in the sterility test. A total of 3 endophytic bacteria were isolated from leaves of G. pentaphylla. Isolates showed distinct morphological and biochemical characteristics. Biochemical characterisation of the isolates was performed by following Bergey’s manual of systematic bacteriology. Two isolates were found gram-positive, and one was gram-negative. All three isolates were found positive for the catalase test and negative for the indole test; two isolates (GP-1, GP-3) were positive for the oxidase test; 2 isolates (GP-1, GP-2) were found positive for both citrate and methyl red test. Some plant growth-promoting activities of the isolates were also performed. All the 3 isolates (GP-1, GP-2, and GP-3) were found positive for the ammonia production test; isolate GP-2 was found positive for phosphate solubilisation test; isolate GP-3 was found positive for both IAA production and lipase activity test. The isolated endophytic bacteria survived in different salt concentrations

In vitro propagation and plant regeneration of Torenia crustacea (L.) Charm. & Schltdl; an important ethnic medicinal plant

Torenia crustacea (L.) Charm. & Schltdl is an important medicinal herb used in India, Indonesia and Malaysia. This herb is used by Bodo tribes in the Bodoland Territorial Region, Assam to treat various diseases like diabetes. The present experiment developed an efficient protocol for in vitro mass propagation technique for Torenia crustacea species using its nodal explants. For tissue culture, the rapidly growing nodal explants of Torenia crustacea were used. Effective explant surface sterilisation was found at 15 min. of treatment with 2% sodium hypochlorite resulting in a maximum explant survival rate and a lower rate of explant contamination after 21 days of explant culture. Media containing full strength MS (Murashige and Skoog's) + BAP (6- Benzyl amino purine) (1 mg/l) were found most effective for the establishment of the explant. The highest shoot proliferation and multiplication were observed in the media containing full strength MS + BAP (1 mg/l) + NAA (Naphthalene acetic acid) (0.2 mg/l); in this combination, an average of 16 shoots formed per nodal explant. The rooting of explants was observed highest in MS media along with 0.4 mg/l concentration of NAA and 1 mg/l BA. The in vitro multiplied shoots were grown in plastic pots containing vermicompost fertiliser and soil mixture and successfully grown in the open field condition

In vitro propagation and somaclonal variation study of Phlogacanthus thyrsiformis Nees an ethnic medicinal plant

Bodoland Territorial Region is very rich in natural bioresources, and the Bodo tribes of the region use numerous ethnic medicinal plants to treat different kinds of diseases. Phlogacanthus thyrsiformis Nees is an important medicinal shrub species used in the region to treat different kinds of diseases. The objectives of the present study were to develop an efficient in vitro mass propagation technique of the species using nodal explant and study genetic stability in the genome of in vitro propagated plantlets by different RAPD markers. Effective explant surface sterilisation resulted at 2 minutes of treatment with 0.1% mercuric chloride. Explant responses were found most effective in the full strength MS + 1mg/l BAP (6- benzyl amino purine), and explant highest shoot proliferation multiplication and rooting were found in the media MS + 1 mg/l BAP + 0.250 mg/l NAA. Ex vitro rooting of micro propagated plants was most effective when the explants were dipped in 1mg/l IBA for an hour. RAPD assays were conducted using eight sets of random primers (OPC02, OPC05, OPC07, OPC08, OPC09, OPX06, DK2 and OPA01). All the primers except OPC07 and OPA01 formed monomorphic DNA bands in gel electrophoresis and polymorphism was detected by OPC07 and OPA01 primer