Understanding how protein-protein interactions depend on the choice of buffer, salt, ionic strength, and pH is needed to have better control over protein solution behavior. Here, we have characterized the pH and ionic strength dependence of protein-protein interactions in terms of an interaction parameter kD obtained from dynamic light scattering and the osmotic second virial coefficient B22 measured by static light scattering. A simplified protein-protein interaction model based on a Baxter adhesive potential and an electric double layer force is used to separate out the contributions of longer-ranged electrostatic interactions from short-ranged attractive forces. The ionic strength dependence of protein-protein interactions for solutions at pH 6.5 and below can be accurately captured using a Deryaguin-Landau-Verwey-Overbeek (DLVO) potential to describe the double layer forces. In solutions at pH 9, attractive electrostatics occur over the ionic strength range of 5-275 mM. At intermediate pH values (7.25 to 8.5), there is a crossover effect characterized by a nonmonotonic ionic strength dependence of protein-protein interactions, which can be rationalized by the competing effects of long-ranged repulsive double layer forces at low ionic strength and a shorter ranged electrostatic attraction, which dominates above a critical ionic strength. The change of interactions from repulsive to attractive indicates a concomitant change in the angular dependence of protein-protein interaction from isotropic to anisotropic. In the second part of the paper, we show how the Baxter adhesive potential can be used to predict values of kD from fitting to B22 measurements, thus providing a molecular basis for the linear correlation between the two protein-protein interaction parameters.

The study revealed the occurrence of 528 species of vascular plants belonging to 356 genera and 111 families in the Sundarban Mangrove Forest of Bangladesh. Among these species, 24 were pteridophytes and the rest were angiosperms, of which only 24 were true mangroves and 70 were mangrove associates. Magnoliopsida and Liliopsida were represented by 373 and 131 species, respectively. These species belonged to 345 herbs, 89 shrubs and 94 trees. Sixty-four species were climbers, 14 were epiphytes, 6 were parasites, and 7 were palms. The species number per family varied from 1 to 42. In pteridophytes, Pteridaceae with 4 genera and 5 species was the largest family. In angiosperms, Fabaceae with 24 genera and 42 species and Poaceae with 27 genera and 42 species were the largest families, respectively, in Magnoliopsida and Liliopsida. Most of the species included in this checklist were found in oligohaline zone, Sarankhola range and the forest margins, and recognized as economically important. Eleven species categorized as threatened in Bangladesh were found to occur in this mangrove forest.

Abstract:The study was undertaken to examine banana cv. Kanthali floral bud apex as an alternative source material for in vitro propagation because huge number of explants die due to microbial contamination in case of shoot tip explants. Contamination free cultures were established by treating the floral bud explants with 0.1% HgCl 2 for 6 min. This study found that inflorescence tissues of experimental plant was almost contamination free but was high in phenolic compounds. Phenolic compounds secretion was successfully stopped by pre-soaking them in an antioxidant solution of 0.125% potassium citrate: citrate. After antioxidant treatment the floral bud explants were cultured on MS medium supplemented with different concentrations and combinations of BA+Kn+IAA/IBA+15%CW. Compact, white/greenish white callus was formed in different amount at all concentrations after 3 weeks of culture. All were again subcultured at same medium and after another 30-35 days at 2.0 mg L 1 BA+2.0 mg L 1 Kn+2.0 mg L 1 IAA+15%CW some callus showed embryogenic structure.

This study was carried out to provide the baseline data on the composition and distribution of the angiosperms and to assess their current status in Rajkandi Reserve Forest of Moulvibazar, Bangladesh. The study reports a total of 549 angiosperm species belonging to 123 families, 98 (79.67%) of which consisting of 418 species under 316 genera belong to Magnoliopsida (dicotyledons), and the remaining 25 (20.33%) comprising 132 species of 96 genera to Liliopsida (monocotyledons). Rubiaceae with 30 species is recognized as the largest family in Magnoliopsida followed by Euphorbiaceae with 24 and Fabaceae with 22 species; whereas, in Lilliopsida Poaceae with 32 species is found to be the largest family followed by Cyperaceae and Araceae with 17 and 15 species, respectively. Ficus is found to be the largest genus with 12 species followed by Ipomoea, Cyperus and Dioscorea with five species each. Rajkandi Reserve Forest is dominated by the herbs (284 species) followed by trees (130 species), shrubs (125species), and lianas (10 species). Woodlands are found to be the most common habitat of angiosperms. A total of 387 species growing in this area are found to be economically useful. 25 species listed in Red Data Book of Bangladesh under different threatened categories are found under Lower Risk (LR) category in this study area.

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