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At least 199 records · Page 11Linked to original sources
PubMed1990

Structurally unique plant cytochrome c oxidase isolated from wheat germ, a rich source of plant mitochondrial enzymes.

Purification and characterization of plant cytochrome c oxidases have been impeded by the difficulty of obtaining enough plant mitochondria. We have found commercial wheat germ to be a rich and convenient source of mitochondrial membranes containing respiratory chain complexes in ratios and amounts similar to mitochondria prepared from etiolated seedlings. Cytochrome c oxidase was purified from these membranes by anion-exchange (MonoQ) fast protein liquid chromatography. The enzyme is highly active (turnover number up to 1000 s-1) and exhibits biphasic cytochrome c reaction kinetics similar to those of beef heart oxidase. As with other plant oxidases, the visible spectrum of wheat germ oxidase in the reduced form is blue-shifted compared to other eukaryotic cytochrome oxidases, with peaks at 441 and 602 nm. The electron paramagnetic resonance spectrum of CuA of the wheat germ enzyme is very similar to that of the maize and beef heart enzymes, suggesting that the copper environment is not altered. Sodium dodecyl sulfate-polyacrylamide gels show a subunit composition in which subunits I-IV resemble those of the yeast enzyme in size and antigenicity, while three to four smaller peptides are dissimilar to yeast and other eukaryotic oxidases. A difference between the subunit composition of the wheat germ and wheat seedling enzymes suggests the existence of a developmental or tissue-specific form of cytochrome oxidase in plants.

Animals↗
PubMed1982

Homozygosity and patch structure in plant populations as a result of nearest-neighbor pollination.

The population genetic consequences of nearest-neighbor pollination in an outcrossing plant species were investigated through computer simulations. The genetic system consisted of two alleles at a single locus in a self-incompatible plant that mates by random pollen transfer from a neighboring individual. Beginning with a random distribution of genotypes, restricted pollen and seed dispersal were applied each generation to 10,000 individuals spaced uniformly on a square grid. This restricted gene flow caused inbreeding, a rapid increase in homozygosity, and striking microgeographic differentiation of the populations. Patches of homozygotes bordered by heterozygotes formed quickly and persisted for many generations. Thus, high levels of inbreeding, homozygosity, and patchiness in the spatial distribution of genotypes are expected in plant populations with breeding systems based on nearest-neighbor pollination, and such observations require no explanation by natural selection or other deterministic forces.

Journal Article↗
PubMed1979

Structure of plant nuclear and ribosomal DNA containing chromatin.

Digestion of plant chromatin from Brassica pekinensis and Matthiola incana with staphylococcus nuclease leads to a DNA repeat of 175 plus or minus 8 and a core size of 140 base pairs. DNase I digestion results in multiples of 10 bases. Ribosomal RNN genes were studied as a model system for active plant chromatin because of their great redundancy and their high transcriptional activity in growing and differentiating tissues. The actively transcribed genes were identified by nascent RNA of ribosomal origin still attached to its matrix DNA. Hybridization techniques were used to demonstrate that even transcriptionally active gene sequences are present in nuclease generated chromatin subunits. Comparison of the DNase I kinetics of chromatin digestion with the amount of ribosomal RNA genes which is available for hybridization at the given times indicated that ribosomal RNA genes are digested, but not preferentially degraded by DNase I.

Base Composition↗
PubMed1974

The structure of plant cell walls: v. On the binding of xyloglucan to cellulose fibers.

Cell wall strength is decreased by both auxin treatment and low pH. In a recently proposed model of the plant cell wall, xyloglucan polymers are hydrogen-bonded to cellulose fibrils, forming the only noncovalent link in the network of polymers which cross-link the cellulose fibers. The decreased strength of the cell wall seen upon lowering the pH might be due to an effect of hydrogen ions on the rate of xyloglucan creep along cellulose fibers. This paper investigates binding of xyloglucan fragments to cellulose. At equilibrium, the per cent of nine- and seven-sugar xyloglucan fragments which are bound to cellulose is sensitive to both temperature and the concentration of nonaqueous solvents. However, neither the per cent of xyloglucan fragments bound to cellulose at equilibrium, nor the rate at which the xyloglucan fragments bind to cellulose, is sensitive to changes in hydrogen ion concentration. These results support the hypothesis that, within the cell wall, xyloglucan chains are connected to cellulose fibers by hydrogen bonds, but these results suggest that this interconnection between xyloglucan and cellulose is unlikely to be the point within the wall which regulates the rate of cell elongation.

Journal Article↗
PubMed1974

The Structure of Plant Cell Walls: VI. A Survey of the Walls of Suspension-cultured Monocots.

The primary cell walls of six suspension-cultured monocots and of a single suspension-cultured gymnosperm have been investigated with the following results: (a) the compositions of all six monocot cell walls are remarkably similar, despite the fact that the cell cultures were derived from diverse tissues; (b) the cell walls of suspension-cultured monocots differ substantially from those of suspension-cultured dicots and from the suspension-cultured gymnosperm; (c) an arabinoxylan is a major component (40% or more by weight) of monocot primary cell walls; (d) mixed beta-1,3; beta-1,4-glucans were found only in the cell wall preparations of rye grass endosperm cells, and not in the cell walls of any of the other five monocot cell cultures nor in the walls of suspension-cultured Douglas fir cells; (e) the monocot primary cell walls studied contain from 9 to 14% cellulose, 7 to 18% uronic acids, and 7 to 17% protein; (f) hydroxyproline accounts for less than 0.2% of the cell walls of monocots. Similar data on the soluble extracellular polysaccharides secreted by these cells are included.

Journal Article↗
PubMed1978

Structure of Plant Cell Walls: VIII. A New Pectic Polysaccharide.

This paper describes the isolation and characterization of rhamnogalacturonan II, a hitherto unobserved component of the primary cell walls of dicotyledonous plants. Rhamnogalacturonan II constitutes 3 to 4% of the primary cell walls of suspension-cultured sycamore (Acer pseudoplatanus) cells. Rhamnogalacturonan II is a very complex polysaccharide yielding, upon hydrolysis, 10 different monosaccharides including the rarely observed sugars apiose, 2-O-methylxylose, and 2-O-methylfucose. In addition, rhamnogalacturonan II is characterized by the rarely observed glycosyl interconnections of 2-linked glucuronosyl, 3,4-linked fucosyl, and 3-linked rhamnosyl residues. These glycosyl linkages have never previously been detected in primary sycamore cell walls. Evidence is presented which suggests that polysaccharides similar to rhamnogalacturonan II are present in the primary cell walls of the three other dicotyledonous plants examined.

Journal Article↗
PubMed1982

Structure of Plant Cell Walls : XII. Identification of Seven Differently Linked Glycosyl Residues Attached to O-4 of the 2,4-Linked l-Rhamnosyl Residues of Rhamnogalacturonan I.

Seven differently linked glycosyl residues have been found to be glycosidically linked to O-4 of the branched 2,4-linked l-rhamnosyl residues contained in the rhamnosyl and galacturonosyl backbone of the cell wall pectic polysaccharide rhamnogalacturonan I. These seven glycosyl residues are, therefore, the first residues of at least seven different side chains attached to the rhamnogalacturonan backbone. These first side chain glycosyl residues are 5-linked l-arabinofuranosyl and terminal 3-, 4-, 6-, 2,6-, and 3,6-linked d-galactopyranosyl residues. The existence of at least seven different side chains in rhamnogalacturonan I indicates that rhamnogalacturonan I is either an exceedingly complex polysaccharide or that rhamnogalacturonan I is a family of polysaccharides with similar or identical rhamnogalacturonan backbones substituted with different side chains.

Journal Article↗
PubMed1986

Structure of Plant Cell Walls : XVIII. An Analysis of the Extracellular Polysaccharides of Suspension-Cultured Sycamore Cells.

The water-soluble polysaccharides (SEPS) secreted into the medium by suspension-cultured sycamore cells were examined to determine whether the polysaccharides were the same as those present in the walls of sycamore cells. The SEPS were made more amenable to fractionation by treatment with a highly purified alpha-1,4-endopolygalacturonase (EPG). The EPG-treated SEPS were fractionated by anion-exchange and gelpermeation chromatography. The following polysaccharides were found: xyloglucan, arabinoxylan, at least two arabinogalactans, a rhamnogalacturonan-II-like polysaccharide, and a polygalacturonic acid-rich polysaccharide. The oligogalacturonide fragments expected from EPG-digested homogalacturonan were also identified. Evidence was obtained for the presence of a rhamnogalacturonan-I-like polysaccharide. All of the above polysaccharides have been isolated from or are believed to be present in sycamore cell walls. Furthermore, all of the noncellulosic polysaccharides known to be present in sycamore cell-walls appear to be present in the SEPS.

Journal Article↗
PubMed1999

A study of deleterious gene structure in plants using Markov chain Monte Carlo.

The characteristics of deleterious genes have been of great interest in both theory and practice in genetics. Because of the complex genetic mechanism of these deleterious genes, most current studies try to estimate the overall magnitude of mortality effects on a population, which is characterized classically by the number of lethal equivalents. This number is a combination of several parameters, each of which has a distinct biological effect on genetic mortality. In conservation and breeding programs, it is important to be able to distinguish among different combinations of these parameters that lead to the same number of lethal equivalents, such as a large number of mildly deleterious genes or a few lethal genes, The ability to distinguish such parameter combinations requires more than one generation of mating. We propose a model for survival data from a two-generation mating experiment on the plant species Brassica rapa, and we enable inference with Markov chain Monte Carlo. This computational strategy is effective because a vast amount of missing genotype information must be accounted for. In addition to the lethal equivalents, the two-generation data provide separate information on the average intensity of mortality and the average number of deleterious genes carried by an individual. In our Markov chain Monte Carlo algorithm, we use a vector proposal distribution to overcome inefficiency of a single-site Gibbs sampler. Information about environmental effects is obtained from an outcrossing experiment conducted in parallel with the two-generation mating experiments.

Algorithms↗
PubMed1993

A high-order structure of plant storage proprotein allows its second conversion by an asparagine-specific cysteine protease, a novel proteolytic enzyme.

During seed embryogenesis, glycinin, the 11-S seed storage protein found in soybeans, undergoes post-translational proteolytic processing, in which a proprotein molecule is cleaved into an acidic and a basic subunit by a one-point cleavage that occurs at the carboxyl side of the asparaginyl residue located at the junction of the subunits. To elucidate the mechanism of this very limited proteolysis, we purified the cysteine endoprotease and used purified proglycinin produced by Escherichia coli as a substrate. This enzyme was separated by isoelectric focusing into three isomeric forms: two had a molecular mass of 33 kDa and the third, 33.8 kDa. The cysteine protease was found both in the proteinaceous vacuoles of cotyledonary tissue of immature seeds and in mature seeds, and is the first proteolytic enzyme to be classified as an asparagine-specific endoprotease. The results also indicate that the above proteolysis is largely attributable to the conformational accessibility of the enzyme to the asparaginyl residue in the cleavage site of proglycinin. The conformation of this single enzyme-accessible region on the proglycinin molecule is relatively flexible and becomes unstable under low salt conditions, or when heat is applied, causing the enzyme to lose its specificity.

Amino Acid Sequence↗
PubMed1999

Bacterial conjugation protein MobA mediates integration of complex DNA structures into plant cells.

Agrobacterium tumefaciens transfers T-DNA to plant cells, where it integrates into the genome, a property that is ensured by bacterial proteins VirD2 and VirE2. Under natural conditions, the protein MobA mobilizes its encoding plasmid, RSF1010, between different bacteria. A detailed analysis of MobA-mediated DNA mobilization by Agrobacterium to plants was performed. We compared the ability of MobA to transfer DNA and integrate it into the plant genome to that of pilot protein VirD2. MobA was found to be about 100-fold less efficient than VirD2 in conducting the DNA from the pTi plasmid to the plant cell nucleus. However, interestingly, DNAs transferred by the two proteins were integrated into the plant cell genome with similar efficiencies. In contrast, most of the integrated DNA copies transferred from a MobA-containing strain were truncated at the 5' end. Isolation and analysis of the most conserved 5' ends revealed patterns which resulted from the illegitimate integration of one transferred DNA within another. These complex integration patterns indicate a specific deficiency in MobA. The data conform to a model according to which efficiency of T-DNA integration is determined by plant enzymes and integrity is determined by bacterial proteins.

Agrobacterium tumefaciens↗