Effects of blue and red light on expression of nuclear genes encoding chloroplast glyceraldehyde-3-phosphate dehydrogenase of Arabidopsis thaliana.

We have characterized the effects of different light spectra on expression of the nuclear genes (GapA and GapB) encoding chloroplast glyceraldehyde-3-phosphate dehydrogenase in Arabidopsis thaliana. Steady-state mRNA levels for both genes in etiolated seedlings increased after a short exposure to red or blue light. However, these increases could not be reversed by immediate far-red light following the initial light treatment. In mature plants, a short light pulse, regardless of its spectrum, had no apparent effect on GapA or GapB mRNA levels in dark-adapted plants. In contrast, continuous exposure to red, blue, or white light resulted in increases of GapA and GapB mRNA levels, with blue and white light being far more efficient than red light. Similarly, continuous exposure of etiolated seedlings to red, blue, or white light also resulted in increased GapA and GapB mRNA levels. In addition, we show that illumination of red light-saturated Arabidopsis plants with continuous blue light results in further increases of GapA and GapB mRNA levels. Based on these results, we conclude that both blue light photoreceptor- and phytochrome-mediated pathways are involved in light regulation of GapA and GapB genes in Arabidopsis, with blue light acting as the dominant regulator.     

Isozyme variation in germplasm accessions of the wild oat Avena sterilis L.

Summary Optimal exploitation of crop genetic resources requires a knowledge of the range and structure of the variation present in the gene pool of interest. Avena sterilis L., the cultivated oat progenitor, contains a store of genetic diversity that is readily accessible to the oat breeder. The objectives of the present paper were: (1) to evaluate isozyme polymorphisms in a sample of A. sterilis accessions from the U.S. National Small Grains Collection, (2) to analyze the distribution of isozyme diversity across the geographic range of the accessions, (3) to classify the accessions into groups based on isozyme variation, and (4) to suggest strategies for efficient sampling of this germplasm collection. One thousand and five accessions from 23 countries and 679 collection sites were screened for variation using 23 enzyme systems. Due to limited information about the genetic relationship among individual members of families of isozymes in hexaploid oat species, data were recorded solely for band presence. The frequencies of bands in accessions from the various countries were used to calculate the probability of genotypic identity (I_x.y), the probability of a unique genotype (U_x.y), and an adjusted polymorphic index (H_x). Accessions from Turkey and Lebanon had the largest polymorphic index values, Turkish and Moroccan accessions displayed the greatest numbers of bands. Accessions from Iran, Turkey, Iraq, and Lebanon had the largest mean probabilities of containing unique genotypes. Based on isozyme data, Turkey appeared to represent the center of diversity in this germplasm collection. Band frequencies calculated among countries were used in a principal component analysis. Accessions from Israel and Morocco clustered together; accessions from Iran, Iraq, Turkey, and Ethiopia formed another group; and Algerian accessions formed an outlying group. Several isozyme bands had a regional distribution. These results suggested that choosing accessions from countries based on their groupings in the principal component analysis should secure a greater range of diversity than sampling from the collection at random. Cluster analyses based on Jaccard's distances calculated for all pairwise combinations of the 1005 accessions revealed six broad genetic groups of accessions. Groups 1 and 6 contained accessions from many countries and encompassed half of all accessions. Groups 2 and 4 were heavily populated by accessions from Israel and Morocco. Groups 3 and 5 were composed almost exclusively of accessions from Iran, Iraq, and Turkey. By selecting representative accessions from these six groups, oat breeders could most effectively sample the range of genetic variation in this A. sterilis collection.     

Conjugative Plasmid Transfer between Bacteria under Simulated Marine Oligotrophic Conditions

Marine Vibrio S14 strains and an Escherichia coli strain were starved in artificial seawater (NSS) with no added carbon, nitrogen, or phosphorus. The broad-host-range plasmid RP1 was transferred between the starving S14 strains and also from the E. coli donor to the S14 recipient under oligotrophic conditions, in which mixtures of donor and recipient cells were held on Nuclepore filters either floated on NSS or held such that NSS flowed through the filter. Transconjugants were obtained from S14 donors and recipients starved for at least 15 days before being mixed together for conjugation, whereas transconjugants were recovered from the E. coli donor and S14 recipient for up to 3 days of prestarvation, but not after 5 days. Transconjugants were obtained when there were as few as about 10⁵ and 10⁴ cells of starving S14 donors and recipients, respectively, per ml held on the filters. Starved donor and recipient mixtures incubated at 4 or 26°C, as well as those allowed to mate for 2, 5, or 24 h, all yielded numbers of transconjugants which were not significantly (P > 0.05) different.     

Attachment of Agrobacteria to Grape Cells

The presence of the Ti plasmid favorably influences the attachment of agrobacteria to grape callus cells, especially during the early stages of a 2-h incubation. Agrobacterium strains attached to a similar extent to both the crown gall-resistant cultivar (Catawba), Vitis labruscana, and the crown gall-susceptible cultivar (Chancellor), Vitis sp. Attachment of the virulent strain to grape callus cells is blocked by the avirulent strain HLB-2 in both the tissue culture cell suspension and the seedling root systems.     

Appropriate characters for racial classification in maize

To determine the relative importance of the genotype, the environment, and their interaction on the expression of morphological characters in maize races, 50 Mexican races and 24 races from Central America, South America, and the U.S. were grown in several locations and seasons in México and 47 characters were measured directly. Estimates of the ratio of variance components, rc = [Vc/(Ve+VCs/], were used as criteria to determine the appropriate characters for racial classification. Twenty-four useful variables were identified. Analysis of the structure of the data matrix facilitated visual examination of correlations among the variables and of the variability represented by each variable. Based on these analyses, a minimum list of 9 characters was suggested to be appropriate variables for racial classification: number of leaves per plant, branched part length/tassel length, central spike internode length, male glume length, kernel width, rachis segment length, pith diameter, ear diameter/length, and kernel width/length.     

Localization of spectrin isoforms in the adult mouse heart

The distribution of two isoforms of spectrin in the adult mouse heart was investigated by Western blotting and immunocytochemistry by use of monospecific antibodies to erythrocyte spectrin and nonerythroid brain spectrin (240/235). Western blotting revealed proteins analogous to both isoforms of -spectrin in adult heart. Light-microscopic immunocytochemistry indicated that erythroid spectrin was distributed throughout the myocardium, with immunofluorescence localized to plasma membranes, Z-lines, and intercalated discs. Antibodies to brain spectrin (240/235) exhibited staining throughout the heart, with a generally diffuse distribution except for the prominent immunoreactivity associated with the intercalated discs. Nonerythroid spectrin immunofluorescence was detected in the endothelial cells of the endocardium and the mesothelial cell lining of the epicardium. Erythrocyte spectrin was not detected in the endocardium or the epicardium. The identification and localization of spectrin isoforms in the mammalian heart suggest the importance of spectrin proteins in the structural integrity and proper function of cardiac cells and tissues. This is the first demonstration of two different -spectrin subunits in the mammalian heart.     

Specific cross-linking of the proline isomerase cyclophilin to a non-proline-containing peptide.

A peptide corresponding to an efficient peroxisomal targeting sequence, the carboxy terminal 12 amino acids of PMP20 from Candida boidinii, was employed as an affinity ligand to search for a peroxisomal targeting receptor. Two proteins from yeast extracts with apparent molecular masses of 20 and 80 kDa were detected by chemical cross-linking to radioiodinated peptide. Both proteins were present in cytosolic supernatants. The 20-kDa species did not cross-link to a control peptide with reversed sequence, whereas the 80-kDa protein cross-linked to both peptides. The cross-linking assay was used to purify the 20-kDa protein from Saccharomyces cerevisiae. Partial protein sequencing identified this protein as cyclophilin, the product of the CYP1 gene. This protein, a peptidyl-prolyl cis-trans isomerase, is the yeast homologue of the protein that mediates the immunosuppressant effects of the drug cyclosporin A (CsA). Cross-linking of peptide to cyclophilin was inhibited by CsA. The cross-linking of cyclophilin to the PMP20-derived peptide was unanticipated because the peptide contains no prolines. The CYP1-encoded protein was not required to target proteins to peroxisomes because this organelle appeared to be assembled normally in a CYP1-disrupted strain. Furthermore, the final three amino acids of the peptide, which are critical for peroxisomal sorting, were not required for cross-linking to cyclophilin. We conclude that either cyclophilin is playing a nonessential facilitating role in peroxisomal targeting or that the interaction of the targeting peptide to cyclophilin is mimicking an interaction with an unidentified substrate or effector of cyclophilin.     

Glycine: An important potential component of spinal shock

Amino acid neurotransmitters (AANTs) play a major role in maintenance of muscle tone. Abnormal AANT concentrations are associated with hyper- or hypotonic states. Flaccidity from spinal shock commonly occurs after spinal cord injury (SCI) and may be associated with changes in AANT concentrations. Ischemic SCIs created in the lumbar region of rabbits by intraaortic balloon occlusion produced spastic or flaccid injuries. Microdialysis sampling of AANTs from the injured segmental structures was done 3 days after SCI. Evoked potentials were used to monitor spinal cord stability. No significant changes in AANT levels occurred in the spastic or flaccid group after 4 hour sampling. However, flaccid animals had baseline glycine levels 2–3 times higher (p<0.001) than spastic animals or controls. High concentrations of the inhibitory AANT glycine is associated with flaccidity following SCI, or spinal shock, but not spasticity. Glycinergic compounds directed toward suppression of excess muscle tone deserve further study.