Assessment of genetic diversity within and between pearl millet landraces

A minimum core subset of pearl millet [Pennisetum glaucum (L.) R. Br.], which comprised 504 landrace accessions, was recently established from the global pearl millet germplasm collection of ICRISAT. The accessions for this core were selected by a random proportional sampling strategy following stratification of the entire landrace collection (about 16,000 accessions) according to their geographic origin and morpho-agronomic traits. In this study RFLP probes were used to quantify the genetic diversity within and between landrace accessions of this minimum core using a subset comprising ten accessions of Indian origin. Twenty five plants per accession were assayed with EcoRI, EcoRV, HindIII and DraI restriction enzymes, and 16 highly polymorphic RFLP probes, nine associated with a quantitative trait loci (QTLs) for downy mildew resistance, and five associated with a QTL for drought tolerance. A total of 51 alleles were detected using 16 different probe-enzyme combinations. The partitioning of variance components based on the analysis of molecular variance (AMOVA) for diversity analysis revealed high within-accession variability (30.9%), but the variability between accessions was significantly higher (69.1%) than that within the accessions. A dendrogram based on the dissimilarity matrix obtained using Ward's algorithm further delineated the 250 plants into ten major clusters, each comprised of plants from a single accession (with the exception of two single plants). A similar result was found in an earlier study using morpho-agronomic traits and geographic origin. This study demonstrated the utility of RFLP markers in detecting polymorphism and estimating genetic diversity in a highly cross-pollinated species such as pearl millet. When less-tedious marker systems are available, this method could be further extended to assess the genetic diversity between and within the remaining accessions in the pearl millet core subset.     

Complex of human apolipoprotein C-1 with phospholipid: thermodynamic or kinetic stability?

Thermal unfolding of discoidal complexes of apolipoprotein (apo) C-1 with dimyristoyl phosphatidylcholine (DMPC) reveals a novel mechanism of lipoprotein stabilization that is based on kinetics rather than thermodynamics. Far-UV CD melting curves recorded at several heating/cooling rates from 0.047 to 1.34 K/min show hysteresis and scan rate dependence characteristic of slow nonequilibrium transitions. At slow heating rates, the apoC-1 unfolding in the complexes starts just above 25 degrees C and has an apparent melting temperature T(m) approximately 48 +/- 1.5 degrees C, close to T(m) = 51 +/- 1.5 degrees C of free protein. Thus, DMPC binding may not substantially increase the low apparent thermodynamic stability of apoC-1, DeltaG(25 degrees C) < 2 kcal/mol. The scan rate dependence of T(m) and Arrhenius analysis of the kinetic data suggest an activation enthalpy E(a) = 25 +/- 5 kcal/mol that provides the major contribution to the free energy barrier for the protein unfolding on the disk, DeltaG > or = 17 kcal/mol. Consequently, apoC-1/DMPC disks are kinetically but not thermodynamically stable. To explore the origins of this kinetic stability, we utilized dynode voltage measured in CD experiments that shows temperature-dependent contribution from UV light scattering of apoC-1/DMPC complexes (d approximately 20 nm). Correlation of CD and dynode voltage melting curves recorded at 222 nm indicates close coupling between protein unfolding and an increase in the complex size and/or lamellar structure, suggesting that the enthalpic barrier arises from transient disruption of lipid packing interactions upon disk-to-vesicle fusion. We hypothesize that a kinetic mechanism may provide a general strategy for lipoprotein stabilization that facilitates complex stability and compositional variability in the absence of high packing specificity.     

Differential expression of DAHP synthase and chorismate mutase in various organs of Brassica juncea and the effect of external factors on enzyme activity

The multibranched shikimic acid pathway was discovered as the biosynthetic route to the aromatic amino acids phenylalanine, tyrosine and tryptophan and a host of other secondary metabolites. An extensive body of work is available on the characterization of various enzymes of this pathway in order to understand the underlying mechanisms of aromatic amino acid biosynthesis and secondary metabolism in higher plants. In the present investigation, selective assays, based on feedback regulation patterns and divalent cation requirements, were used to monitor the isozyme profiles of two of the key regulatory enzymes of this pathway. 3-Deoxy- d -arabino heptulosonate-7-phosphate synthase (DAHP synthase/DS) (EC 4.1.2.15) and chorismate mutase (CM) (EC 5.4.99.4) have been characterized from different vegetative and reproductive organs of Brassica juncea cv. Pusa Bold. An attempt has also been made to investigate the effect of external factors, such as light and wounding on the regulation of these enzymes. The results reveal differential expression of DAHP synthase and CM in various organs of Brassica and an adaptability of plants to various stresses by up or down regulation of these enzymes.     

Characterization of a bacterial xylanase resistant to repression by glucose and xylose

Summary Bacillus subtilis CD4, when grown in nutrient broth or minimal medium in presence of xylan, produced extracellular xylanase that hydrolyzed xylan optimally at pH 5. The enzyme was induced by xylan, xylose and glucose. Addition of xylose or glucose in xylan containing medium did not affect enzyme production. The structural gene encoding xylanase was cloned and expressed in E. coli. The recombinant enzyme exhibited similar properties like that of native enzyme including resistance to repression by xylose and glucose.     

Enhanced photocatalytic activity of ceria-doped zinc oxide under UV illumination prepared via chemical precipitation

Transition metal oxide has emerged as one of the most potential candidates for environment remediation by utilizing solar energy through photocatalysis. This study compares the optical characteristics of zinc oxide (ZnO) and ceria-doped zinc oxide (CeZnO) nanoparticles synthesized through a facile chemical precipitation method without using any assistant catalyst. The present work investigates the consequences of ceria (cerium dioxide, CeO₂) intrusion on the photocatalytic activity of ZnO nanoparticles using methylene blue (MB) as a probe pollutant. The CeZnO showed an increase in photoactivity when compared to ZnO nanoparticles for degradation of MB in an aqueous solution under ultraviolet (UV) irradiance. The resulting heterojunction between ZnO and that of ceria enhances the charge separation efficiency showing a strong correlation between ZnO and CeO₂ heterojunction on the charge transfer mechanism across the interface.     

Alzheimer's disease cerebrospinal fluid antibodies display selectivity for microglia

Previous investigations demonstrated that the cerebrospinal fluid (CSF) from Alzheimer's disease (AD) patients contains antibodies that recognize specific neuronal populations in the adult rat central nervous system (CNS). These findings suggest a pathogenic role for immunological aberrations in this disorder. To determine if antibodies may provide a means to differentially diagnose the dementias, CSF from a diversified dementia population was screened against the developing rat CNS and a cell culture system. Markings produced by AD CSF were distinctly different from those of vascular dementias (VAD) against the developing rat CNS. More importantly, some AD CSF recognized amoeboid microglia. The recognition of amoeboid microglia by antibodies in AD CSF is particularly interesting since these cells proliferate in response to nervous system disease and also engulf debris. A cell culture technique was developed to allow the rapid screening of CSF antibodies. Patient CSF produced five different types of markings in the cell culture: microglia, glioblasts, fibers, nonspecific, or negative. Correlations with these structures and the diagnosis of four different dementia populations revealed that, in comparison to the other groups, AD CSF displayed remarkable selectivity toward microglial cells. Cortical biopsies from patients suspected to have AD were incubated with the patient's own CSF and that of confirmed AD patients. Both CSF samples recognized microglial cells in the patient's cortical biopsy. The same CSF samples incubated against normal human cortical autopsy or a biopsy from a 3-mo-old child displayed negative immunoreactivity. These three approaches suggest that the presence of CSF microglial antibodies may be a means to distinguish AD patients from other dementias. The results add further support to the widely growing concept that inflammation and similar immune mechanisms may contribute to AD pathogenesis.     

Alzheimer disease: evidence for susceptibility loci on chromosomes 6 and 14

We report the transmission of HLA haplotypes and Gm allotypes in 97 members of a single kindred containing 257 individuals, 45 of whom were determined by clinical examination, autopsy, or historical data to have had Alzheimer disease (AD). Extensive inbreeding suggests that more than one gene may contribute to susceptibility to AD in this family, despite the apparent vertical transmission of illness. The distribution of HLA haplotypes and of Gm allotypes to affected and unaffected siblings is consistent with the possibility that genes in the HLA region of chromosome 6 and perhaps also in the Gm region of chromosome 14 are determinants of susceptibility. Further studies are needed to investigate whether susceptibility to AD may result from an interaction between (immune response?) genes on these two chromosomes.     

Induction of swelling in pea internode tissue by ethylene

Ethylene inhibits polar cell expansion of etiolated pea (Pisum sativum) internode tissue and results in a radial cell expansion, swelling. A special gas-tight growth chamber was developed to monitor continuously the induction of cell expansion inhibition of excised internode segments in the presence of ethylene. Following a complex induction period which lasts about 3 hours, a low, but steady-state growth rate is achieved. Ethylene removal experiments indicate that the gas induces an irreversible change in the cell expansion mode. If the tissue was transferred to an ethylene-free chamber after the steady-state rate had been achieved, this rate continued in the absence of the gas. If the gas was removed during an intermediate phase, that intermediate rate of growth continued after removal. In other experiments, segments were incubated with intact apical hooks and the induction period was much shorter than with isolated segments. Changes in imino acid metabolism have been correlated with the induction of swelling. Although total proline and hydroxyproline levels were not affected by ethylene treatment, incorporation of [¹⁴C]proline into a wall-associated protein was inhibited during the period when swelling occurred. These results suggest that ethylene is affecting proline pool sizes.     

Role of the human and murine cyclin T proteins in regulating HIV-1 tat-activation.

Human cyclin T1 markedly stimulates tat-activation in rodent cells which are normally poorly responsive to the effects of Tat. This result suggests that there are likely to be critical differences in the murine and human cyclin T1 proteins. Here, we analyzed the role of the murine and human cyclin T1 proteins in addition to the human cyclin T2a and T2b proteins on regulating tat-activation. Only the human cyclin T1 protein efficiently formed a complex with Tat bound to TAR RNA. This difference in function was due to the presence of a cysteine residue in human cyclin T1 at position 261 rather than a tyrosine or asparagine residue which are found in the murine cyclin T1 protein and the human cyclin T2a and T2b proteins, respectively. A mouse cyclin T1 protein containing a substitution of tyrosine residue 261 with a cysteine residue, was able to interact with Tat and stimulate tat-transactivation in rodent cells. Likewise, substitution of a cysteine residue for an asparagine residue at position 260 of the cyclin T2a and T2b proteins also resulted in their ability to interact with Tat and stimulate tat-activation in rodent cells. The data indicate that a specific residue in the cyclin T proteins is required for their in vitro interaction with Tat and their ability to stimulate in vivo tat-activation.