Showing papers by "Shashi B. Pandey published in 2023"

Evolution of Rotating 25 M$_{\odot}$ Population III star: Physical Properties and Resulting Supernovae

Abstract: In this Letter, we report the outcomes of 1-D modelling of a rotating 25 M$_{\odot}$ zero-age main-sequence Population III star up to the stage of the onset of core collapse. Rapidly rotating models display violent and sporadic mass losses after the Main-Sequence stage. In comparison to the solar metallicity model, Pop III models show very small pre-supernova radii. Further, with models at the stage of the onset of core collapse, we simulate the hydrodynamic simulations of resulting supernovae. Depending upon the mass losses due to corresponding rotations and stellar winds, the resulting supernovae span a class from weak Type II to Type Ib/c. We find that the absolute magnitudes of the core-collapse supernovae resulting from Pop III stars are much fainter than that resulting from a solar metallicity star. From our simulation results, we also conclude that within the considered limits of explosion energies and Nickel masses, these transient events are very faint, making it difficult for them to be detected at high redshifts.

In Silico Dissection of Regulatory Regions of PHT Genes from Saccharum spp. Hybrid and Sorghum bicolor and Expression Analysis of PHT Promoters under Osmotic Stress Conditions in Tobacco

Abstract: Phosphorus (P) is the second-most essential macronutrient required for the growth and development of plants. It is involved in a number of cellular processes that contribute to the plant’s growth and development. This study investigated Saccharum spp. hybrid and Sorghum bicolor promoter regions of Phosphate transporters (PHT), viz., PHT1, PHT2, PHT3, PHT4, and PHO1, through in silico analysis. The transcription start sites (TSS), conserved motifs, and CpG islands were studied using various computational techniques. The distribution of TSSs indicated the highest promoter prediction scores (1.0). MSh2 and MSb4 were recognized as the common promoter motifs for PHT promoters, found in with 85 to 100% percentage of distribution. The CpG analysis revealed that the promoter regions of most PHT genes had low CpG density, indicating a possible tissue-specific expression. The PHT promoters were investigated for the presence of biotic- and abiotic-stress-associated transcription factor binding sites (TFbs) that revealed the presence of binding motifs for major transcription factors (TFs), namely, AP2/ERF, bHLH, bZIP, MYB, NAC, and WRKY. Therefore, the in-silico analysis of the promoter regions helps us to understand the regulation mechanism of phosphate transporter promoters and gene expression under stress management. The 5′ regulatory region of the EaPHT gene was isolated from Erianthus, a wild relative of the genus Saccharum. The promoter construct was prepared and transformed in tobacco wherein the promoter drove the expression of GUS. Analysis of GUS expression in transgenic tobacco revealed enhanced expression of GUS under salt-stress conditions. This is the first report of the isolation and characterization of a phosphate transporter gene promoter from Erianthus and is expected to be useful for the development of salt-stress transgenic crop plants.

Evolution and Final Fates of a Rotating 25 M$_{\odot}$ Pop III star

Abstract: In this proceeding, we present the 1-dimensional stellar evolution of two rotating population III (Pop III) star models, each having a mass of 25 M$_{\odot}$ at the zero-age main-sequence (ZAMS). The slowly rotating model has an initial angular rotational velocity of 10 per cent of the critical angular rotational velocity. In contrast, the rapidly rotating model has an initial angular rotational velocity of 70 per cent of the critical angular rotational velocity. As an effect of rotationally enhanced mixing, we find that the rapidly rotating model suffers an enormous mass loss due to the deposition of a significant amount of CNO elements toward the surface after the main-sequence phase. We also display the simulated light curves as these models explode into core-collapse supernovae (CCSNe).

Induction of Polyploidy in Citrus Rootstocks through In Vitro Colchicine Treatment of Seed-Derived Explants

Abstract: Polyploidy, frequently observed in citrus species, aids in achieving better adaptation to environmental stresses. In this context, the current work aims to develop stable tetraploids in citrus rootstock cultivars, viz., Rough lemon, Rangpur lime and Alemow, through in vitro colchicine treatments. Seed-derived explants were obtained by culturing sterile seeds on MS basal media. Seedlings with a size of 5–8 mm (hypocotyl) were exposed to colchicine treatment. After treatment, the surviving seedlings were minigrafted onto six-month-old rootstock for better growth. Colchicine concentrations of 0.1%, 0.2%, 0.3% and control for durations of 16 or 24 h were tested with respect to the induction of polyploidisation. Treatment with 0.1% colchicine for 24 h resulted in high rates of mutation for polyploidisation and showed the highest tetraploid induction percentage (18.3%) in all the rootstock cultivars. High colchicine concentration and long exposure time decreased the survival of the observed seedlings. Flow cytometry and cytological methods were used for confirmation of autotetraploidy in the analysed samples. The surviving seedlings were identified on the basis of morphological and cytological variables, such as leaf area and stomata size, which significantly increased with increasing ploidy level. The proposed method was found to be an effective way to induce the polyploidy in Rangpur lime, Rough lemon and Alemow rootstocks.