City spore concentrations in the European Economic Community (EEC). VI. Poaceae (Grasses), 1982–1986

Summary Airborne grass-pollen concentrations in six cities in the EEC are compared, based on observations from five years, 1982–1986. Results show that there are quantitative differences both between the monitoring stations and between the years. Very provisionally, the average seasonal total of the European urban airborne grass-pollen concentration can be put at 4 to 5000 per m³ of air. Also qualitatively, regarding the seasonal fluctuations, there are differences between the stations, and between the years. Generally, the results confirm that June is the most typical grass-pollen month in northwestern Europe, whereas in mediterranean Europe May is the more prominent grass-pollen period. There seems to be little coherence between the starting dates of the grass-pollen season even at relatively nearby stations in northwestern Europe, suggestive for a great influence of the actual weather situation.     

Taxonomy of someDiploschistes spp. (lichenized ascomycetes,Thelotremataceae) containing gyrophoric acid

Three species which contain both gyrophoric and lecanoric acids and possess perithecioid ascomata are recognized in the genusDiploschistes. D. badius andD. gyrophoricus are described as new, whileD. subcupreus is reduced to synonymy withD. sticticus. Two species occur in the southern hemisphere, whileD. badius is found in N. America.     

Isolation and characterization of the Escherichia coli mutL gene product

The Escherichia coli mutL gene product has been purified to near homogeneity from an overproducing clone. The mutL locus encodes a polypeptide of 70,000 daltons as determined by denaturing gel electrophoresis. The native molecular weight of MutL protein as calculated from the sedimentation coefficient of 5.5 S and Stokes radius of 61 A is 139,000 daltons, indicating that MutL exists as a dimer in solution. In addition to its ability to complement methyl-directed DNA mismatch repair in mutL-deficient cell-free extracts, DNase I protection experiments demonstrate that the purified MutL protein interacts with the MutS-heteroduplex DNA complex in the presence of ATP.     

Identification and regulation of whole-cell chloride currents in airway epithelium

We used the whole-cell patch-clamp technique to study membrane currents in human airway epithelial cells. The conductive properties, as described by the instantaneous current-voltage relationship, rectified in the outward direction when bathed in symmetrical CsCl solutions. In the presence of Cl concentration gradients, currents reversed near ECl and were not altered significantly by cations. Agents that inhibit the apical membrane Cl conductance inhibited Cl currents. These conductive properties are similar to the conductive properties of the apical membrane Cl channel studied with the single-channel patch-clamp technique. The results suggest that the outwardly rectifying Cl channel is the predominant Cl-conductive pathway in the cell membrane. The steady-state and non-steady-state kinetics indicate that current flows through ion channels that are open at hyperpolarizing voltages and close with depolarization. These Cl currents were regulated by the cAMP-dependent protein kinase: when the catalytic subunit of cAMP-dependent protein kinase was included in the pipette solution, Cl channel current more than doubled. We also found that reducing extracellular osmolarity by 30% increased Cl current, suggesting that cell-swelling stimulated Cl current. Studies of transepithelial Cl transport in cell monolayers suggest that a reduction in solution osmolarity activates the apical Cl channel: reducing extracellular osmolarity stimulated a short-circuit current that was inhibited by Cl-free solution, by mucosal addition of a Cl channel antagonist, and by submucosal addition of a loop diuretic. These results suggest that apical membrane Cl channels may be regulated by cell volume and by the cAMP-dependent protein kinase.     

A possible role for the pcnB gene product of Escherichia coli in modulating RNA: RNA interactions.

Summary The sequence of the PcnB protein of Escherichia coli, a protein required for copy number maintenance of ColE1-related plasmids, was compared with the PIR sequence database. Strong local similarities to the sequence of the E. coli protein tRNA nucleotidyltransferase were found. Since a substrate of the latter protein, tRNA, structurally resembles the RNAs that control ColE1 copy number we believe that we may have identified a region in PcnB that interacts with these RNAs. Consistent with this idea is our observation that PcnB is required for the replication of R1, a plasmid whose replication is also regulated by a small RNA.     

Specific truncations of an acetolactate synthase gene from Brassica napus efficiently complement ilvB/ilvG mutants of Salmonella typhimurium

Summary The expression of an acetolactate synthase (ALS) gene isolated from the cruciferous plant Brassica napus was investigated in Salmonella typhimurium. Using an expression plasmid containing the highly active trc (trp-lac) promoter, several plant ALS constructs were made containing successive in-frame truncations from the 5 end of the coding region. Functional complementation by these plant ALS constructs of a S. typhimurium mutant devoid of ALS enzymic activity was assayed on minimal medium. Truncations which eliminated a large portion of the transit peptide coding sequence proved to act as efficient ALS genes in the bacterial host. Truncations close to the putative processing site of the plant protein were inactive in the complementation test. A full length copy of the gene, including the entire transit peptide coding region, was also inactive. The efficiency of the complementation, estimated by comparison to the growth rate of wild-type S. typhimurium, was found to correlate with levels of ALS activity in the transformed bacteria. Specific mutations, known to produce herbicide resistance in plants, were introduced into the truncated ALS coding sequence by site-directed mutagenesis. When expressed in bacteria these constructs conferred a herbicide resistance phenotype on the host. The potential of this system for mutagenesis and enzymological studies of plant proteins is discussed.     

Identification of Brassica oleracea monosomic alien chromosome addition lines with molecular markers reveals extensive gene duplication

Summary Chromosomes of Brassica oleracea (2n=18) were dissected from the resynthesized amphidiploid B. napus Hakuran by repeated backcrosses to B. campestris (2n=20), creating a series of monosomic alien chromosome addition line plants (2n=21). Using morphological, isozyme and restriction fragment length polymorphism markers (RFLPs), 81 putative loci were identified. Of nine possible synteny groups, seven were represented in the 25 monosomic addition plants tested. Sequences homologous to 26% of the 61 DNA clones utilized (80% were cDNA clones) were found on more than one synteny group, indicating a high level of gene duplication. Anomalous synteny associations were detected in four 2n=21 plants. One of these plants showed two markers from one B. oleracea chromosome associated with a second complete B. oleracea synteny group, suggesting translocation or recombination between non-homologous chromosomes in Hakuran or the backcross derivatives. The other three 2n=21 plants each contained two or more B. oleracea synteny groups, suggesting chromosome substitution.     

Relationship of vector insert size to homologous integration during transformation of Neurospora crassa with the cloned am (GDH) gene

Summary We used lambda and plasmid vectors containing the am ⁺ gene in an insert of from 2.7 to 9.1 kb, to transform am point mutant and deletion strains. A total of 199 transformants were examined with the potential to yield am ^– transformants by homologous recombination. When we used vectors that had 9.1 kb of homology with the chromosomal DNA, 30% of the transformants obtained were the result of homologous recombination regardless of whether the vector was a lambda molecule, a circular plasmid, or a plasmid that had been linearized prior to transformation. When vectors with up to 5.1 kb of homology were used, very few transformants (1 of 89 tested) resulted from homologous recombination. Of a sample of 29 ectopic integration events obtained by transformation with the 9.1 kb fragment cloned in a vector, 18 included a major part (usually almost all) of both arms of lambda with the entire Neurospora 9.1 kb insert between them. Four included only long arm sequence together with an adjacent segment of the insert containing the am gene. The remaining seven were the result of multiple integrations. There was no evidence of circularization of the vector prior to integration. All transformants that had multiple copies of the am gene appeared to be subject to the RIP process, which causes multiple mutations in duplicated sequences during the sexual cycle.     

Control of barley root respiration

Evidence from barley [ Hordeum distichum (L.) Lam. cv. Maris Mink], and from many other species, suggests that respiration is controlled by either supply of carbohydrate or demand for ATP. The relationship between root respiration rate (measured as O₂ consumption or CO₂ production) and ethanol-soluble carbohydrate content altered with time following selective pruning, and the change could not be accounted for by buffering of the cytoplasmic carbohydrate concentration by sugars in the vacuole. Exogenous sucrose supplied to the roots prevented any decline of the respiration rate in shoot-pruned plants, and if supplied for 24 h stimulated the respiration rate after any treatment. Root extension responded to sucrose in a similar manner. We suggest that respiration is under fine control by adenylates, but the capacity of the respiratory system is fixed by the supply of sucrose, possibly via coarse control of the respiratory machinery, or of the processes requiring metabolic energy.