Tobacco-mosaic-virus-induced increase in abscisic-acid concentration in tobacco leaves:

The concentrations of free and bound abscisic acid (ABA and the presumed ABA glucose ester) increased three- to fourfold in leaves of White Burley tobacco (Nicotiana tabacum L.) systemically infected with tobacco mosaic virus. Infected leaves developed a distinct mosaic of light-green and dark-green areas. The largest increases in both free and bound ABA occurred in dark-green areas. In contrast, virus accumulated to a much higher concentration in light-green tissue. Free ABA in healthy leaves was contained predominantly within the chloroplasts while the majority of bound ABA was present in non-chloroplastic fractions. Chloroplasts from light-green or dark-green tissues were able to increase stromal pH on illumination by an amount similar to chloroplasts from healthy leaf. It is unlikely therefore that any virus-induced diminution of pH gradient is responsible for increased ABA accumulation. Tobacco mosaic virus infection had little effect on free ABA concentration in chloroplasts; the virus-induced increase in free ABA occurred predominantly out-side the chloroplast. The proportional distribution of bound ABA in the cell was not changed by infection. Treatment of healthy plants with ABA or water stress increased chlorophyll concentration by an amount similar to that induced by infection in dark-green areas of leaf. A role for increased ABA concentration in the development of mosaic symptoms is suggested.Abbreviations ABA abscisic acid - TMV tobacco mosaic virus     

Induction of 2',5' oligo(A) synthetase in tumor-bearing mice with encephalomyocarditis (EMC) virus or poly(I)poly(C)

Infection of 13 month-old C3H mice with EMC virus or inoculation with the interferon inducer poly(I)poly(C) results in elevated levels of the enzyme 2',5' oligo(A) synthetase only in animals with spontaneous tumors (breast cancer or hepatomas). High enzymatic activities are detected in homogenates from liver, spleen, plasma and neoplastic cells of the animals with breast carcinomas and only in the neoplastic liver cells of the animals with hepatomas.     

Human leukocyte interferon subtypes have different antiproliferative and antiviral activities on human cells

The antigrowth effects of 5 different cloned human leukocyte IFN subtypes (IFN-alpha A, B, C, D, F) and 2 molecular hybrids between them (IFN-alpha AD(Bg1II) and IFN-alpha DA(Bg1II)) were examined on 6 different human cell lines. The results indicate that the interferons sort into two distinct groups: IFN-alpha B, C and F showed comparable antiproliferative activity which was greater than that of IFN-alpha A, D, AD(Bg1II) and DA(Bg1II). The interferons could also be assigned to one of two groups on the basis of their antiviral activity. IFN-alpha A, D and AD(Bg1II) were observed to be more protective than IFN-alpha B, C and F against HSV-2 and EMCV infections, i.e. the relative antiviral efficacies of the cloned IFN subtypes were the reverse of their antiproliferative activities.     

Target size analysis by radiation inactivation: a large capacity tube rack for irradiation in a Gammacell 220

Target size analysis by radiation inactivation is now a well-established method to study structure-function relationships in biologically active macromolecules without prior purification or even solubilization. Recently, it was reported that a relatively low-dose-rate but commonly available gamma source such as the Gammacell 220 (Atomic Energy of Canada, Ltd.) can be used to carry out radiation inactivation experiments providing it is appropriately calibrated with enzymes of known radiation sensitivities (G. Beauregard and M. Potier (1982) Anal. Biochem. 122, 379-384). In this report, a tube rack designed to fit into the irradiation chamber of the Gammacell 220 which allows five experiments (at 30 tubes per experiment) to be carried out simultaneously with both standard and unknown samples is described. The dose rates delivered at different positions in the rack were determined by irradiating rat liver cytosolic neuraminidase, an enzyme of known radiation sensitivity. A better than 2.7% agreement was obtained between experimental dose rate and computed values from isodose curves previously published by other authors (O. A. Curzio and H. O. Quaranta (1982) Int. J. Appl. Radiat. Isot. 33, 1-3).     

Isolation and characterization of light- and dithiothreitol-modulatable glucose-6-phosphate dehydrogenase from pea chloroplasts

Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP oxidoreductase, EC 1.1.1.49) has been purified to electrophoretic homogeneity from pea chloroplasts. The enzyme, which has a Stokes radius of 52 Å, is a tetramer made up of four 56000 Da monomers. The pH optimum is around 8.2. The enzyme is absolutely specific for NADP. The apparent K_m(NADP) is 2.4 ± 0.1 μM. NADPH inhibition of the enzyme is competitive with respect to NADP (mean K_i, 18 ± 5 μM) and is mixed (K_p >K_m, V_max >V_p) with respect to glucose 6-phosphate (mean crossover point, 0.5 ± 0.1 mM). The apparent K_m(glucose 6-phosphate) is 0.37 ± 0.01 mM. The purified enzyme is inactivated in the light in the presence of dilute stroma and washed thylakoids, and by dithiothreitol. Enzyme which has been partially inactivated by treatment with dithiothreitol can be further inactivated in the light in the presence of dilute stroma and washed thylakoids and reactivated in the dark, but only to the extent of the reverse of light inactivation. Dithiothreitol-inactivated enzyme is not reactivated further by addition of crude stroma or oxidized thioredoxin. Dithiothreitol-dependent inactivation of the enzyme follows pseudo-first-order kinetics and shows rate saturation. The enzyme which has been partially inactivated by treatment with dithiothreitol does not differ from the untreated control with respect to thermal and tryptic inactivation. However, enzyme which has been partially light inactivated shows different thermal and tryptic inactivation patterns as compared to the dark control. These observations suggest that the changes in the enzyme brought about by light modulation are not necessarily identical with those brought about by dithiothreitol inactivation.     

Ammoniacal silver staining of proteins: mechanism of glutaraldehyde enhancement

When the conditions for detecting proteins by ammoniacal silver staining (B. R. Oakley, D. R. Kirsch, and N. R. Morris (1980) Anal. Biochem. 105, 361-363.) following gel electrophoresis were varied, it was noted that glutaraldehyde pretreatment was necessary for maximal staining, which could not be explained simply as the result of "fixation." Further studies indicated that glutaraldehyde enhancement of protein staining with this silver reagent was probably due to oxidation of the aldehyde groups by silver ions, resulting in metallic silver depositions within the gel which act as nucleation sites for additional metallic silver localization in the protein bands upon the addition of formaldehyde developer. This proposed mechanism is consistent with the Tollen's reaction, as well as some aspects of the photographic process. Consistent with this notion, silver-staining intensities are directly related to mole percentage lysine of various standard proteins.     

Effects of Light on Dopamine Metabolism in the Chick Retina

The effect of prolonged exposure to light on the activity of dopaminergic neurons and dopamine (DA) metabolism of chick retinae was investigated. alpha-Fluoromethyldopa, a potent and specific irreversible inactivator of aromatic amino acid decarboxylase, was used to assess DA turnover after inhibition of synthesis, and also to assess in vivo tyrosine hydroxylase activity by dihydroxyphenylalanine accumulation. After 48 h of light exposure, retinal DNA in 12-day-old chicks was about 30% higher (p less than 0.005) whereas dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were elevated two to three times (p less than 0.005) the level of controls kept in the dark for the same period. DA turnover was about twofold faster in the light (t 1/2 = 31 min) than in the dark (t 1/2 = 65 min). Tyrosine hydroxylase, assayed in vitro with saturating levels of cofactor and substrate, increased by about 50% after light exposure. The apparent tyrosine hydroxylase activity in vivo was approximately sixfold higher in the light than the dark. These results are interpreted and discussed in terms of the regulation of DA synthesis, and the use of DOPAC and HVA as indices of DA function in the retina.     

A Tipula paludosa population with a high incidence of two pathogens

The incidence of lethal parasites in the larvae of a Tipula paludosa population was monitored for two seasons. The proportions of larvae infected with Tipula iridescent virus (TIV) and a tachinid insect were similar to those in previously studied populations, whereas the proportions of larvae infected with Tipula nuclear polyhedrosis virus (NPV) and a spore-forming bacterium (SFB) were higher. Conservative estimates of mortality due to these four agents were 10.7% in 1977–1978 and 7.7% in 1978–1979. The mean population density and the proportion of SFB-infected larvae were lower in 1978–1979 than in 1977–1978, while the proportion of NPV-infected larvae was higher. In 1979 the proportion of NPV-infected larvae was positively correlated with population density, which was highest in the wettest part of the study area. In both seasons the proportion of SFB-infected larvae was negatively correlated with population density. Larvae infected with the NPV or the SFB became pallid at an advanced stage of infection, but, although infected larvae were found throughout the larval period, pallid larvae were only found in the later part. It is suggested that larvae become infected in an early instar, then the infections slowly develop throughout the remainder of the larval period. Five larvae were found with mixed infections; four were infected with the SFB and NPV, while the fifth was infected with the SFB and TIV.     

Virus particle packaging in baculovirus and cytoplasmic polyhedrosis virus inclusion bodies

The structure of the inclusion bodies (IBs) of three multiply enveloped nuclear polyhedrosis viruses (MNPVs), one singly enveloped NPV (SNPV), two granulosis viruses (GVs) and one cytoplasmic polyhedrosis virus (CPV) were compared. A method was devised to calculate the numbers of virus particles and nucleocapsids in IBs using data from light microscopy and thin sections. The three MNPVs, from Agrotis segetum (English and Polish virus isolates) and Mamestra brassicae had similar concentrations of virus particles ranging from 17.3 to 19.6 per μm³ of IB. Plusia gamma SNPV had a higher density of 59.6 virus particles per μm³ of IB, which partly compensated for its having smaller IBs (mean volume 0.65 μm³) than the MNPVs (2.60–9.71 μm³). The English A. segetum MNPV isolate had the most nucleocapsids in each virus particle (mean, 4.04) and the largest IBs (mean volume, 9.71 μm³), giving 674 nucleocapsids per IB on average. The GVs, from A. segetum and Pieris brassicae, mainly contained one nucleocapsid per IB. P. gamma CPV IBs had a much higher density of virus particles than the baculoviruses (260 per μm³ compared with 17–60 per μm³). These data are discussed in relation to the biological properties of these viruses, and possible adaptational advantages of alternative IB designs are considered.