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Biomedical subjects

N D Young

Publications and source records attributed to N D Young.

26 records · Page 2Linked to original sources
PubMed1987

Immunogold localization of the intracellular sites of structural and nonstructural tobacco mosaic virus proteins.

Antibodies raised against the 126K nonstructural protein (replicase) encoded by tobacco mosaic virus (TMV) RNA or the viral coat protein have been used to localize these proteins within virus-infected tobacco leaf cells by an immunogold labeling technique. A protocol is given for low-temperature fixation to facilitate immunogold labeling. In cells of TMV-infected leaf tissue, the 126K protein immunogold label was found almost exclusively in "viroplasms" in the cytoplasm and in pockets of virus particles at the viroplasmic periphery. When utilizing the coat protein antiserum, very little labeling was seen within the viroplasms, although virus particles throughout the cytoplasm were heavily labeled. Viroplasms contained electron-dense rope-like structures embedded in a ribosome-rich matrix. In their "mature" form, viroplasms are the well-known "X body" inclusions. The rope-like structures were up to 1.2 micron long and appear twisted, undergoing several revolutions throughout their length, but were not of a constant pitch. In transverse section, they appeared to be composed of several hollow, radially segmented cylinders 21 nm in diameter, with a 9-nm hole. Antibody labeling showed them to be composed, at least in part, of the 126K protein. Clusters of virus particles at the edge of or within the viroplasms were also labeled with the 126K antiserum, in contrast to virus particles in other areas of the cell, which were not. TMV-infected tobacco mesophyll protoplasts cultured for up to 27 hr did not contain the rope-like ribbons. Instead, isolated protoplasts contained amorphous cytoplasmic areas which were labeled with 126K antibody. Since the 126K protein is most probably a constituent of the TMV RNA-replicating enzyme (replicase), its intracellular location is considered to be indicative of the site of replication of TMV RNA. Therefore these results suggest that replication occurs at the edges of the viroplasms.

Antibody Specificity↗
PubMed1984

Physiological control of arginine decarboxylase activity in k-deficient oat shoots.

The effect of K-deficiency on the putrescine biosynthetic enzyme, arginine decarboxylase (ADC), was investigated by growing oat (Avena sativa L. var Victory) plants on a low-K, but otherwise complete nutrient medium in washed quartz sand for up to 18 days. Enzyme activity rose as the concentration of KCl was dropped to 0.6 millimolar or below. However, growth was not inhibited significantly at 0.6 millimolar KCl. ADC activity increased in the whole shoot of K-deficient oats throughout the period of 6 to 18 days, but remained constant in normal plants. At 18 days, ADC activity in entire K-deficient shoots was 6 times greater than in normal shoots, while in the first (oldest) leaf, ADC specific activity increased to more than 30 times the specific activity in the first leaf of normal plants. This effect was due to a moderate rise in total ADC activity in the first leaf between 6 and 18 days, accompanied by a significant decline in protein content. Replacing K(+) with Na(+) or Li(+) significantly inhibited the increase in ADC activity in K-deficient oats, while Rb(+) depressed the specific activity to a level below that in normal plants. An alternative putrescine biosynthetic enzyme, ornithine decarboxylase, was also examined. The specific activity of a pelletable form of the enzyme was increased 2-fold in the shoots of K-deficient oats.

Journal Article↗
PubMed1983

Putrescine and Acid Stress : Induction of Arginine Decarboxylase Activity and Putrescine Accumulation by Low pH.

Incubation of peeled oat Avena sativa L. var Victory leaf segments on media of pH 5.0 or below leads to a rapid and massive increase in the titer of putrescine while incubation at pH values above 5.0 causes little or no change. The low pH effect is independent of the buffer system employed. Putrescine levels rise within 3 hours and reach their peak 8 to 9 hours after acidification. At this time, putrescine titer is eight times greater at pH 3.5 than at 6.0. None of the other polyamines shows a response to changes in external pH. The increase in putrescine is blocked by the addition of cycloheximide or dl-alpha-difluoromethylarginine, a specific inhibitor of the putrescine biosynthetic enzyme, arginine decarboxylase. In one experiment, arginine decarboxylase activity was 110% greater at pH 4.0 than at 6.0 after a 4-hour incubation, although the average increase over many experiments was 47%. The activity of the other possible putrescine biosynthetic enzyme, ornithine decarboxylase, falls throughout the incubation period and is virtually equal at pH 4.0 and 6.0.

Journal Article↗
PubMed1983

Are polyamines transported in etiolated peas?

To investigate the possible transport of polyamines and their precursor amino acids, (14)C-labeled putrescine, spermidine, arginine, or lysine were injected into cotyledons of 4-day etiolated pea (Pisum sativum L. cv Alaska) seedlings. After 4 hours the shoot, root, and cotyledons were homogenized and the extracted, dansylated polyamines separated by thin-layer chromatography. Little radioactivity was transported from the cotyledons when [(14)C]putrescine or [(14)C]spermidine were injected and of the radioactivity in the axis, none could be recovered as polyamines. Injection of [(14)C]arginine or [(14)C]lysine, on the other hand, led to a significant transport of radioactivity into the axis, of which a large fraction was present in the form of the diamines, putrescine or cadaverine, respectively. These results indicate that polyamines in the growing regions of etiolated pea seedlings probably arise from transport and conversion of amino acid precursors.

Journal Article↗
PubMed1982

Rapid cellular translocation is related to close contacts formed between various cultured cells and their substrata.

Interference-reflection microscopy combined with time-lapse cinemicrography was used to examine the relationship between cell-to-substratum contact patterns and the speeds of translocation for a variety of cell types. Rapid translocation of amphibian leukocytes (average speed = 9.0 micron/min), amphibian epidermal cells (7 micron/min) and teleost epidermal cells (7 micron/min) was found to correlate with patterns of broad grey close contacts. Similar contact patterns were found under freshly seeded (2 h) chick heart fibroblasts (moving 1-3 micron/min), the rapidly advancing (1-5 micron/min) margin of spreading human WI-38 fibroblasts, and isolated MDCK canine epithelial cells (0.5-1.0 micron/min). Conversely, numerous dark streaks of focal contact were found associated with the slow rate of translocation displayed by older cultures (72 h) of chick fibroblasts (less than 0.1 micron/min), well-spread WI-38 cells (less than or equal to 0.3 micron/min) and confluent MDCK cells (less than 0.01 micron/min). It is concluded that close contacts, but not focal contacts, are associated with rapid cellular translocation, and that the build-up of focal contacts is associated with reduced cellular translocation and maintenance of the spread cell shape.

Animals↗
PubMedDate not supplied

Genetic dissection of oligogenic resistance to bacterial wilt in tomato.

To study resistance to bacterial wilt (caused by Pseudomonas solanacearum) in tomato, we analyzed 71 F2 individuals from a cross between a resistant and a susceptible parent with 79 DNA markers. F2 plants were inoculated by two methods: bacteria were injected into shoots of cuttings or poured into soil surrounding wounded roots. Disease responses were scored on a scale of 0 to 5. Statistical comparisons between DNA marker genotypes and disease phenotypes identified three genomic regions correlated with resistance. In plants inoculated through roots, genomic regions on chromosomes 6 and 10 were correlated with resistance. In plants inoculated through shoots, a region on chromosome 7 was significant, as were the regions on chromosomes 6 and 10. The relative impact of resistance loci on disease response differed between shoot and root inoculations. To confirm the existence of a partial resistance gene on chromosome 6, an F2 individual homozygous for the resistant parent's alleles on chromosomes 7 and 10, but heterozygous for markers on chromosome 6, was selfed. Analysis of the F3 progeny confirmed that a partial resistance locus was located on chromosome 6, very close to CT184. The presence of a partial resistance locus on chromosome 10 was similarly confirmed by analysis of progeny of another F2 plant chosen on the basis of its marker phenotype.

Chromosome Mapping↗