Bidirectional motion of filaments: Role of motor proteins and passive cross linkers

In eukaryotic cells, motor proteins (MP) bind to cytoskeletal filaments and move along them in a directed manner generating active stresses. During cell division a spindle structure of overlapping antiparallel microtubules (MT) form whose stability and dynamics under the influence of MPs has been studied extensively. Although passive cross linkers (PCL) were known to provide structural stability to filamentous network, consequences of the interplay between ATP dependent active forces of MPs and passive entropic forces of PCLs on MT overlap remains largely unexplored. Here, we formulate and characterize a model to study this, using linear stability analysis and numerical integration. In presence of PCLs, we find dynamic phase transitions with changing activity exhibiting regimes of stable partial overlap with or without oscillations, instability towards complete overlap, and stable limit cycle oscillations that emerge via a supercritical Hopf bifurcation characterized by an oscillation frequency determined by the MP and PCL parameters. We show that the overlap dynamics and stability depend crucially on whether both the MTs of overlapping pair are movable or one is immobilized, having potential implications for in vivo and in vitro studies.Comment: 13 pages, 9 figure

Phonon Anomalies, Orbital-Ordering and Electronic Raman Scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: Temperature-dependent Raman Study

We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a wide spectral range of 120-5200 cm-1 from 5K to 300K, covering the tetragonal to orthorhombic structural transition as well as magnetic transition at Tsm ~ 160K. The mode frequencies of two first-order Raman modes B1g and Eg, both involving displacement of Fe atoms, show sharp increase below Tsm. Concomitantly, the linewidths of all the first-order Raman modes show anomalous broadening below Tsm, attributed to strong spin-phonon coupling. The high frequency modes observed between 400-1200 cm-1 are attributed to the electronic Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The splitting between xz and yz d-orbital levels is shown to be ~ 25 meV which increases as temperature decreases below Tsm. A broad Raman band observed at ~ 3200 cm-1 is assigned to two-magnon excitation of the itinerant Fe 3d antiferromagnet.Comment: Accepted for Publication in JPC

ANTIOXIDANT ACTIVITY OF RHIZOME EXTRACTS OF COLEUS FORSKOHLII BRIQ

Objective: The present study was on the analysis of the phytochemical constituents of Coleus forskohlii which was collected from five different areas in Tamil Nadu, where it is grown for commercial purposes.Methods: C. forskohlii tubers were collected from five areas (Thiruvannamalai, Kanchipuram, Kallakuruchi, Salem, and Vandalur) of Tamil Nadu. Dried tubers were extracted with different solvents such as aqueous, ethanol, and acetone (polar) and petroleum and chloroform (non-polar). Extracts were evaluated for total phenol and flavonoid content and antioxidant activity evaluation by 1,1-diphenyl-2-picrylhydrazyl (DPPH) reduction.Results: The highest DPPH radical scavenging activity (87.6%) was observed in ethanol extract of rhizome collected from Thiruvannamalai area. Total phenol and flavonoid contents were found to be, respectively, 38.82±0.22 mg gallic acid equivalents/g and 21.34±0.32 quercetin equivalent/g.Conclusion: The study clearly indicated the antioxidative potential of different extracts of C. forskohlii and this property may be useful in the preparation of drug formulations, health tonics, and cosmetics

Anomalous Raman scattering from phonons and electrons of superconducting FeSe0.82_{0.82}

We report interesting anomalies in the temperature dependent Raman spectra of FeSe$_{0.82}$ measured from 3K to 300K in the spectral range from 60 to 1800 cm$^{-1}$ and determine their origin using complementary first-principles density functional calculations. A phonon mode near 100 cm$^{-1}$ exhibits a sharp increase by $\sim$ 5% in frequency below a temperature T$_s$ ($\sim$ 100 K) attributed to strong spin-phonon coupling and onset of short-range antiferromagnetic order. In addition, two high frequency modes are observed at 1350 cm$^{-1}$ and 1600 cm$^{-1}$, attributed to electronic Raman scattering from ($x^2-y^2$)to $xz$ / $yz$ $d$-orbitals of Fe.Comment: 19 pages, 4 figures, 1 tabl

Enzymes of Ammonia Assimilation in Fungi: An Overview

Nitrogen is a major element found in many of the simple compounds and nearly all of the complex macromolecules of living cells. Nitrogen can be obtained either from organic source or inorganic source but ultimately it is converted into ammonia and glutamate. Ammonia is the preferred   source of nitrogen. The assimilation of ammonia into glutamate and glutamine plays a central role in the nitrogen metabolism of all organisms. Glutamate dehydrogenase (GDH), Glutamate synthase (GOGAT), and glutamine synthetase (GS) are the key enzymes involved in ammonia assimilation. The specific steps in these pathways vary with the organism, but in virtually all cells glutamate (85%) and glutamine (15%) serve as the nitrogen donors for biosynthetic reactions. In fungi lot of work has been carried out on these enzymes from lower fungi to the higher ones and there are differences in the role played by theses enzymes. Thus knowledge of the formation of glutamate and glutamine from various nitrogen sources is crucial to our understanding of cell growth.  In this review an overall view of the elements present in ammonia assimilation especially in fungi will be carried out along with recent developments and concepts

Comparative morphology and phenetics of Nymphoides species in Kerala

Aquatic plants play an important role in maintaining the ecosystem balance. Nymphoides Seguier (Menyanthaceae) is an emergent, rhizomatous or stoloniferous genus, commonly known as “floating hearts”, identified by its rounded or cordate, floating leaves, petiole like branches and unique floral characters. The present study deals with the comparative morphology and the phenetics of Nymphoides spp. in Kerala. These species are classified into two groups with the help of the dendrogram, which showed 66% dissimilarities among the two groups. N. parvifolia and N. balakrishnanii are closely related species in one group and N. krishnakesara and N. macrosperma are closely related species in other group

Seed storage studies in Mesua ferrea L. a medicinal tree of Indo-Malayan region

This paper, deals with testing the storage and viability of the seeds of Mesua ferrea L. in 5 different storage conditions. Seeds of M. ferrea are recalcitrant in nature and lose viability with a short span 8-15 days. Of the different conventional methods tried using the polycarbonate bottle and bags, M. ferrea seeds retained viability for 150 days with a slow moisture loss from the seeds stored in closed polycarbonate bottles at 10 °C. Here, we have standardised a conventional technique whereby the viability of the seeds can be extended to 150-180 days by storing the seeds in polycarbonate bottles at 10 °C