Interrelationship between chromocentres and chiasmata in radish (Raphanus sativus L.)

A comparative study of the number and distribution of chromocentres in interphase nuclei and mean chiasma frequency at diakinesis has been made in three varietal populations of radish (Raphanus sativus L.), Scarlet Globe, Japanese White and Chinese White. The study showed a significant difference between the varietal populations in mean chiasma frequency and number of chromocentres (P<0.001), indicating that these nuclear characters are genotypically controlled. The correlation analysis revealed a significant negative correlation between chromocentres and chiasma frequency (r= -0.87). It was concluded that an increase in the amount of constitutive heterochromatin, as inferred by chromocentre counts, adversely affects the chiasma frequency and, consequently, genetic recombination in radish.     

X-Pro peptides. A theoretical study of the hydrogen bonded conformations of (α-aminoisobutyryl-l-prolyl)n sequences

Intramolecularly hydrogen bonded conformations of (Aib-Pro)_n sequences have been analysed theoretically. Both 4→1 (C₁₀ and 3→1 (C₇ hydrogen bonded regular structures are shown to be stereochemically feasible. Conformational energies for the helical structures have been estimated using classical potential energy methods. Both C₁₀ and C₇ conformations have very similar energies. Pyrrolidine ring puckering has a pronounced effect on the energies, and only Cγ-endo puckered Pro residues can be accommodated. The theoretical calculations using spectroscopic data suggest that the recently proposed novel 3₁₀ helical conformation for benzyloxycarbonyl(Aib-Pro)₄-methyl ester is in solution, is indeed energetically and stereochemically favourable.     

Reversibility of coated vesicle dissociation

The dissociation of the coated vesicles to clathrin and uncoated vesicles and their reassociation have been studied under various conditions. The extent of reassociation is pH dependent and increases slightly with increasing concentrations of the components. Unlike the self-association of clathrin which is strongly salt dependent, the reassociation of clathrin and uncoated vesicles is practically independent of salt concentration. The coated vesicle gradually loses its coat with increasing pH, and the dissociation process is not an all or none reaction. Ca2+ inhibits dissociation of the coated vesicles and enhances the reassociation of clathrin and uncoated vesicles. Our results show that, although many conditions result in reassociation of protein and lipid vesicle, few conditions result in vesicles of both the same size and composition as native coated vesicles.     

autoregulation of rat adenohypophyseal thyrotropin-releasing hormone receptor

The possible mechanism of attenuation of thyrotropin response to exogenous thyrotropin-releasing hormone after repeated administrations of the releasing hormone has been studied. To this end, the effect of prolonged hormone treatment on the binding of hormone to its receptor in the anterior pituitary gland has been evaluated. The data show that prolonged hormonal treatment resulted in a reduction in the number (B_max) but not the binding affinity (K_D) of the receptor. The effect was reversible and depended on the duration of treatment. This phenomenon of down regulation or the decrease in the receptor number was found not to be due to either the metabolism of releasing hormone or its ability to activate pituitary-thyroid-axis.     

Studies on a novel SrZr2CaLa2O8:Eu3+ phosphor for lighting applications emitting direct white light

Direct white light emitting phosphors play a significant role in the display industry due to their ability to improve the quality, efficiency, and versatility of lighting sources used in most of the displays. The currently investigated phosphor SrZr₂CaLa₂O₈:Eu³⁺ was prepared by a conventional solid-state reaction method. It has been observed that the stoichiometric ratio of all precursors plays an important role in determining the characteristics of the final phosphor. From X-ray diffraction (XRD) analysis, the phosphor was observed to have a hexagonal phase and a crystal size of ~28 nm. Scanning electron microscopy (SEM) observations revealed a cluster of rod-like structures with an average diameter of ~0.2 μm. The excitation peak maximum observed at 280 nm is due to charge transfer between Eu³⁺-O²⁻ ions. The energy transitions ⁷F₀ → ⁵L₆ and ⁷F₀ → ⁵D₂ are responsible for the appearance of other excitation peaks at ultraviolet (UV) (395 nm), blue (~467 nm), green (~540 nm), orange (~590 nm), and red (~627 nm) attributed to ⁵D₀ → ⁷F_J (J = 0–4) transitions of europium ion (Eu³⁺). The Commercial International de I'Eclairage (CIE) chromaticity coordinates were estimated to be (0.37, 0.0.33) and (0.67, 0.33) for the emissions corresponding to 395 and 590 nm, respectively. The characteristic emissions of Eu³⁺ ions allow this novel phosphor to be used to generate direct white light in light-emitting diodes (LEDs), which is otherwise difficult to achieve in single-component systems.     

Optical analysis of RE3+ (RE = Eu,Tb):MgLa2V2O9 nano-phosphors

Red and green rare-earth ion (RE³⁺) (RE = Eu, Tb):MgLa₂V₂O₉ micro-powder phosphors were produced utilizing a standard solid-state chemical process. The X-ray diffraction examination performed on the phosphors showed that they were crystalline and had a monoclinic structure. The particles grouped together, as shown in the scanning electron microscopy (SEM) images. Powder phosphors were examined using a variety of spectroscopic techniques, including photoluminescence (PL), Fourier-transform infrared, and energy dispersive X-ray spectroscopy. Brilliant red emission at 615 nm (⁵D₀ → ⁷F₂) having an excitation wavelength (λ_exci) of 396 nm (⁷F₀ → ⁵L₆) and green emission at 545 nm (⁵D₄ → ⁷F₅) having an λ_exci = 316 nm (⁵D₄ → ⁷F₂) have both been seen in the emission spectra of Tb³⁺:MgLa₂V₂O₉ nano-phosphors. The emission mechanism that is raised in Eu³⁺:MgLa₂V₂O₉ and Tb³⁺:MgLa₂V₂O₉ powder phosphors has been explained in an energy level diagram.     

Does Auxin Play a Role in the Release of Apical Dominance by Shoot Inversion in Ipomoea nil?

According to the auxin-inhibition hypothesis of apical dominance,apically produced auxin moves down the stem and inhibits axillarybud outgrowth, either directly or indirectly. This hypothesishas been examined further by monitoring changes in basipetalauxin transport and endogenous auxin concentration in Ipomoeanil caused by shoot inversion, a stimulus that releases apicaldominance. The results indicate that inversion reduces auxintransport in the main stem. In upright shoots of intact plants,a 16-h pretreatment with [³H]IAA 4 cm below the apex resultsin downward movement of label and accumulation in nodes, especiallythe cotyledonary node. Label does not accumulate in the lateralbuds. GC-MS determinations of endogenous free auxin level inthe fourth node, where a lateral bud grows out following inversionof the upper part of the shoot, show no changes at 3 and 8 hafter inversion, the range of times for inversion-induced budrelease, or at 24 h, when bud outgrowth is continuing. However,inversion did cause a just-detectable decrease (approx. 10%)in the IAA level of the shoot's elongation region. Althoughauxin transport in segments of the main stem is partially inhibitedby inversion over a period shorter than the latent time of budrelease, thus providing a means for the expected depletion ofauxin in the fourth node, no depletion could be detected there.These results suggest that either a decrease in IAA level inthe main stem is not causal of bud release or that the decreasedIAA pool responsible for bud release is compartmented and cannotbe measured in whole-tissue extracts.Copyright 1993, 1999 AcademicPress Apical dominance, auxin content, auxin transport, axillary bud release, GC-MS, Ipomoea nil, Pharbitis nil, shoot inversion     

Cloning of the human thiamine transporter, a member of the folate transporter family.

We have isolated a cDNA from human placenta, which, when expressed heterologously in mammalian cells, mediates the transport of the water-soluble vitamin thiamine. The cDNA codes for a protein of 497 amino acids containing 12 putative transmembrane domains. Northern blot analysis indicates that this transporter is widely expressed in human tissues. When expressed in HeLa cells, the cDNA induces the transport of thiamine (K(t) = 2.5 +/- 0.6 microM) in a Na(+)-independent manner. The cDNA-mediated transport of thiamine is stimulated by an outwardly directed H(+) gradient. Substrate specificity assays indicate that the transporter is specific to thiamine. Even though thiamine is an organic cation, the cDNA-induced thiamine transport is not inhibited by other organic cations. Similarly, thiamine is not a substrate for the known members of mammalian organic cation transporter family. The thiamine transporter gene, located on human chromosome 1q24, consists of 6 exons and is most likely the gene defective in the metabolic disorder, thiamine-responsive megaloblastic anemia. At the level of amino acid sequence, the thiamine transporter is most closely related to the reduced-folate transporter and thus represents the second member of the folate transporter family.     

Human Immunodeficiency Virus Type 1-Induced Hematopoietic Inhibition Is Independent of Productive Infection of Progenitor Cells In Vivo

Human immunodeficiency virus (HIV)-infected individuals exhibit a variety of hematopoietic dysfunctions. The SCID-hu mouse (severe combined immunodeficient mouse transplanted with human fetal thymus and liver tissues) can be used to model the loss of human hematopoietic precursor cell function following HIV infection and has a distinct advantage in that data can be obtained in the absence of confounding factors often seen in infected humans. In this study, we establish that HIV type 1 (HIV-1) bearing a reporter gene inserted into the viral vpr gene is highly aggressive in depleting human myeloid and erythroid colony-forming precursor activity in vivo. Human CD34(+) progenitor cells can be efficiently recovered from infected implants yet do not express the viral reporter gene, despite severe functional defects. Our results indicate that HIV-1 infection alone leads to hematopoietic inhibition in vivo; however, this effect is due to indirect mechanisms rather than to direct infection of CD34(+) cells in vivo.